DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer - Page 1
Forum section: electronics / general

author: SaabFAN
author_rank: Frequent Contributor
timestamp: September 27, 2015, 05:10:15 pm
content: Hello,I have toyed with the idea of getting a spectrum analyzer for quite a long time now, but even the cheapest ones on ebay are way outside my budget: Even defective ones are seldom below 700€, working ones start at 1200€ and go up quite fast.There are a few PCBs out of China inside my budget-range, but those normally start at 500Mhz and go up to 1.5Ghz or higher. Again nothing for me there.So I decided to build one. If I don't mess up the final exam, I have 5 months of time ahead of me which I can dedicate to fiddling with electronics and this project should keep me occupied for most of that time. Plus it's probably a good learning exercise. And who knows: Maybe I can do math afterall? (The VCO seems to require quite a bit of calculation)To add a little challenge, I have set the max. Budget (For stuff to buy in addition to what I already have) to 70€. This means that I will have to build most of the device with stuff from my father and grandfather.The specs so far:Frequency Range: Dual Ranges: Audio-Spectrum & 100khz up to 225Mhz2 Input-Modes: 50Ohms for full Frequency Range & High Impedance (Input connected directly to fast Input-Amp) for low Frequencies up to 15Mhz - Switchable with Reed-RelayStepped Attenuator in the Input-Stage (Explanation: I plan to measure DC/DC-Converter and 12V-Rails on a sailing boat with this device to make sure the MPPT and Battery-Chargers - Another, mostly finished project - dont interfere with the Echo-Sounder and other navigation-equipment)2 Stage Superhet-Receiver with Digitizer at the end8/16bit parallel ADC with 2x 2K x 8bit SRAM as sample-memory (I have a ADC0804LCN 8bit ADC in my partbox, so I will start with that one and later put a 16bit ADC in there)Digitally controlled SweepIntegrated Display (I bought a 3.5Inch Touchscreen last year, which has lost its purpose because the project I wanted to use it for will use a bigger screen) with GUIARM-CPU (Arduino Due)Fits into Schroff 19'' 2 Height-Unit Case220V, 12V (Optional, if it doesn't eat too much power: Internal Battery - I have a few Lithium Accumulators available from my not so successful attempt to modify a MHS-5200A Signal Generator)*UPDATE* Tracking-Generator - Frequency: TBDTheory of operation (Aquisition):INPUT -> Input-Attenuator/Amplifier -> Mixer with PLL-Controlled VCO (SA612 or 615 if the 612 is too "weak" for a 500Mhz LO / The PLL is a Philips TSA5514) -> 250Mhz Bandpass -> Downconverting Mixer -> 10.7Mhz Crystal Filter -> Variable Gain Amplifier -> Detector/Rectifier -> ADC -> SRAM(AQ)Theory of operation (Output):SRAM(AQ) -> Arduino -> Display / Serial DatastreamThe whole design will borrow heavily from "The Simple Man's Spectrum Analyzer" by Hans Summershttp://www.hanssummers.com/spectrumanalyser.html, as well as s PC-Bus based Spectrum Analyzer from DKD Instruments described in a PDF I found online (Written by Dan Doberstein and John Cardone - Link:http://www.n5dux.com/ham/files/pdf/Spectrum%20Analyzer.pdf).I hope this will be at least a nice exercise and interesting learning experience that results (Best case scenario) in a functioning Spectrum Analyzer for less than 150€.I will post first schematics sometime next week and will release the Software here too, once I have written it.Do you guys have any ideas, suggestions, etc.? I'm rather new anything above 20Mhz. I looked over a few service-manuals for Philips Signal Generators and read a few Application Notes regarding HF, but that's basically it.The first challenge will probably be to build a VCO that is able to reach the 450Mhz required to upconvert the input-signal to the 250Mhz of the first IF.Btw. T&M-Equipment available: Rigol DS1104Z, Philips PM3320 200Mhz DSO, Fluke 87, Cheap Ebay 2.4Ghz Frequency Counter, 12Mhz Arb-Waveform-Gen.

author: SundayProgrammer
author_rank: Contributor
timestamp: September 27, 2015, 05:51:38 pm
content: Interesting project. Looking forward to see progress...Axel.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 28, 2015, 04:08:35 am
content: Although I have an HP8590A now, it's not suitable for narrow bandwidths; I think I may yet build one for lower frequencies, perhaps audio to 10s of MHz or 100MHz. I don't have any direct advice just yet, but this sounds like a good project.Tim

author: m98
author_rank: Frequent Contributor
timestamp: September 28, 2015, 12:43:04 pm
content: Btw, with the Rigol DS1104Z you already have a Spectrum Analyzer:http://rheslip.blogspot.ca/2015/09/software-spectrum-analyzer-for-rigol.html

author: tggzzz
author_rank: Super Contributor
timestamp: September 28, 2015, 01:12:04 pm
content: Depending on what you are using it for, there might be much cheaper alternatives in the 25MHz-1.5GHz range.Seehttps://entertaininghacks.wordpress.com/category/frequency-domain-analysers/for some preliminary results. I must get around to writing up later results and "publishing" the post-processing code.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: September 28, 2015, 05:36:18 pm
content: @m98: That software looks interesting. I will certainly give it a try to see if I can use it to verify the operation of my device.Unfortunately, this solution doesn't seem very mobile to me and I would like something that is independent from a PC.@tggzzz: I have thought about SDR and also have checked out the about 100€ NWT4000 available on ebay. Unfortunately, those devices only start at several megaherts (138Mhz in the case of the NWT4000), which puts them outside the frequency range I want to measure.The ranges I'm interested in start closely below 100khz and (at least for the moment) end at about 170Mhz. This covers marine navigation equipment and marine radio frequencies, which start at 415khz and go up to 162Mhz. With the analyzer I want to see if my Energy Harvester and Chargers create any kind of interference (The charger my father bought 6 years ago makes the digital Echo Sounder go crazy once it starts activating the dummy-load and not even a massive LC-Lowpass was able to stop that) in these bands or if external signal sources can get inside the system and make the Power Point Tracker do crazy stuff.I also want to see if I can pull this off. So far I have always opted for the cheap "just buy it"-solution when I needed stuff (Multimeter, Signal-Gen, Digital Counter, Scope), now I want to build something myselfAbout the device itself: I don't know about it yet, but I think adding a tracking generator might be a good idea to check frequency response from Filters. I have 3 TSA5514 PLL Chips here, as well as several 4046 and one 74HCT297-"Digital PLL". The latter ones won't go beyond 20 or 30Mhz, since they are available, why not put them in there?*Specs in first post updated*

author: edpalmer42
author_rank: Super Contributor
timestamp: September 28, 2015, 05:40:59 pm
content: Have you checked out Scotty's Spectrum Analyzer?http://scottyspectrumanalyzer.com/It's a modular DIY system that can be built without sophisticated test equipment.Ed

author: Stupid Beard
author_rank: Regular Contributor
timestamp: September 28, 2015, 05:56:10 pm
content: Quote from: SaabFAN on September 28, 2015, 05:36:18 pmYou could use a mixer to upconvert the lower frequencies into something the SDR can handle. Alan W2AEW has a couple of videos on that, for e.g.:Edit: Nice project though, will be interested to see how it pans out.

author: sain
author_rank: Newbie
timestamp: September 29, 2015, 01:13:28 am
content: It doesn't have the reach you want (70Mhz upper limit), but Farhan (VU2ESE)'s SPECAN project might be of interest:http://hfsignals.blogspot.in/p/specan-reboot-of-w7zoi.html

author: SaabFAN
author_rank: Frequent Contributor
timestamp: September 29, 2015, 08:55:53 pm
content: Quote from: sain on September 29, 2015, 01:13:28 amThat one is quite interesting indeed. I have just ordered the SI570 Oscillator (Found one on Ebay, Digikey didn't have one) and I'm now reading through the rest of it.I didn't know about i2c programmable oscillators, so thx for pointing me to that source. I also just realized that with 15bit available in the TSA5514 I would have had quite big jumps in the frequency instead of a smooth sweep^^

author: SaabFAN
author_rank: Frequent Contributor
timestamp: September 30, 2015, 02:02:24 am
content: The Specan is a really nice piece of equipment. I'm certainly going to use some parts of it. The switchable bandpass for example, or the 20Mhz crystal-based 100Mhz oscillator for the second IF. And the software, of course. With a little luck, I can expand it to my needs without breaking too much.What I can't quite figure out at the moment: How important is the width of the first IF-Filter? Would 10Mhz (requires "exotic" capacitor-values in the area of 0.3pf, which may easily exceeded by parasitics) be enough or can it be wider?My understanding of the matter at the moment is this: Medium (several Mhz) quality selection of the first IF, very high quality (down to 1khz) selection with crystals of the second IF. Correct?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 30, 2015, 03:51:25 am
content: You want the bandwidth narrow to begin with, or decreasing, along the IF strip. That way, as the signal becomes stronger, out-of-band noise is rejected rather than amplified (potentially leading to clipping and mixing, giving large IMD).Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 01, 2015, 12:44:10 am
content: Update:It is not exactly "Junkbox", but I think this one is a much better 1st-Stage Bandpass-Filter than I can build:https://www.digikey.de/product-detail/de/B39311B3768Z810/495-2356-1-ND/821882313,85Mhz Center Frequency and 100khz Bandwidth Bandpass-Filter. And it is tiny! Saves a lot of shielding - Which brings me to a question: If I use plastic poles (I have 5 drawers full of Lego) as stabilizing elements and Aluminium-Foil from the kitchen as the conductive shield, could that be a replacement for copper-plates?The big problem with this component: It raises the maximum LO-Frequency to about 540Mhz, which is 40Mhz above the specified input-frequency of the SA602. Can anyone here measure how this out-of-spec frequency affects the output? I don't have the equipment for that (yet^^).If this distorts the output, what could be done to correct that? I guess it would be possible to use a different Mixer, like the LT5560, which is only 2,75€ when ordered from Digikey (Carrying the advantage of raising the max. Frequency to about 400Mhz with a fitting Filter), or I try to build one myself. I have 4 DB27316 Ultrafast Schottky-Diodes (Datasheet:http://www.semicon.panasonic.co.jp/ds4/DB27316_E.pdf) with 0.8ns Reverse Recovery-Time, as well as a few toroids salvaged from old PC-Mainboards and WireWrap-Wire. I also have 10 BF998 MOSFETs in one of my Partboxes.For the second IF-Filter, I tested several ceramic filters and so far, a 8Mhz HC49-Filter yielded the best result (This websitehttp://www.giangrandi.ch/electronics/crystalfilters/xtalladder.htmlcalculates about 3khz for an 8pole-Filter with my not too accurate measurements) - The 10.7Mhz ceramics I bought on ebay for 3€ for 10 pieces yield only 200khz.Knowing this, the second IF-Stage is slowly coming together. The first stage still has a few question marks hanging over it

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 04, 2015, 06:41:57 pm
content: Quote from: tggzzz on September 28, 2015, 01:12:04 pmRTLSDR can be used as a spectrum analyzer for that frequency range. The main disadvantage is that it's really slow if you want to look at a big chunk of bandwidth.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 09, 2015, 01:02:18 am
content: Okay, little Update here: I have begun to build the device.First I'm going to make a Low Frequency Stage similar to the Specan, because I didn't get the LVDS-Version of the Si570 Oscillator (Programmable Oscillators seem to be a dying breed). Once that one, and the software, are running, I might try to build my own VCO with a large enough sweep-range to be tuned with one of the PLLs I have to add another stage that then can be used up to the original required 225Mhz.This, unfortunately, also means that I have to build my own Bandpass with the parts I have here. I guess, the best I can manage here will be something around 2Mhz Bandwidth at 80Mhz IF.This whole inductor-stuff is still completely new territory for me. Up to now, I almost exclusively used Ohms law to design my circuitsPictures will follow over the weekend.Btw. I managed to put the Oscillator on the component-side and solder the pads through the holes. Looks a lot cleaner than dead-bug-style and was a lot easier than anticipated.

author: ale500
author_rank: Frequent Contributor
timestamp: October 11, 2015, 01:28:23 pm
content: You can make some boards, I mean with like Eagle or so, and send them to one of the chinese fabs. for like 10 € you can get 5x5 cm boards. Shipping to Germany seems to take like 2 1/2 weeks or so. You get 10 pieces for that price. There is a thread on mikrocontroller.net about them. I used Smart Prototyping a couple months ago.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 13, 2015, 09:27:21 pm
content: It might just come to that. I didn't think it would be so difficult and fiddly to build a Bandpass-Filter with a center-frequency of 80Mhz.At first I tried to align it without shielding and thought I had it more or less on 80Mhz. When I tested the whole thing, still without shielding to have easier access to the coils, the whole thing produced something that looked like the output of a Mixer and not the output of a Filter: 215Mhz Sine at the output of the Filter at an input-frequency around 75Mhz. And almost no chance to see the real peak.After adding the shield, this situation improved quite a bit, but the center-frequency was at about 92,3Mhz (The 20€ Frequency-Counter from Ebay was REALLY useful there and also looks nice with its Vacuum-Flourescent Disyplay). So I tried to pull the coils a bit and ripped one off the board, which resulted in another 10 minutes trying to reattach it with all the shielding already in place. And it still isn't fully aligned.Another problem: Without the Scope-Probes attached to the i2c-Bus, I cannot program the oscillator. Seem like I need some ferrites to filter out RF-Nastyness from the i2c-lines (I have an old Pentium III-Mainboard, which will provide those).Summary of the past few days: Power-Electronics is childs-play compared to RF-Stuff. There is just so much stuff you can get away in the sub 20Mhz-Range that makes an RF-Circuit do everything except what you want it to do^^

author: fcb
author_rank: Super Contributor
timestamp: October 14, 2015, 02:45:19 pm
content: Many moons ago I bought a TTi TSA1000 speccy (they also did a TSA250, with... 250MHz range).The bottom end is 400KHz, but I reckon you could tweak that down.Very low cost design I recall.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 16, 2015, 01:02:37 am
content: After struggling with the Filter for several days now, I decided to redo it from scratch.I also altered my scope a bit: As I couldn't use the PLLs to get me the required 434,42Mhz (Available Steps: 50khz or 62,5khz), I decided to use the TV-Tuner from an old TV-Card, which is now usesless because 1st There are no drivers anywhere available anymore and Analog TV has been shut down.The Analyzer will now have 2 Input-Stages: LowBand (0.1khz to 50Mhz), HighBand (50Mhz to 869Mhz). It is basically the Spectrum Analyzer from DKD Instruments with a few modifications: It doesn't need a IBM PC and uses an Arduino instead, the PLLs are already integrated into the Tuner-Module, it contains a Tracking-Generator (I paid for the Si570, now I'm going to use it!^^), instead of an 8bit ADC, it uses a 10bit ADC with optional 12bit High-Resolution-Mode (use of Oversampling), LowBand and HighBand use a common input that is switched via Relays instead of having two dedicated inputs for each band.

author: AF6LJ
author_rank: Unknown
timestamp: October 16, 2015, 01:08:39 am
content: That sounds good, there was a period back from the mod 80s to 2000 where everybody and their brother was building an SA with a TV tuner module as the heart of the unit.For "Cheap" it is the way to go.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 16, 2015, 01:26:12 am
content: On a more positive note, I tested aluminium-foil reinforced by Lego-bricks. It worked rather well. I don't have any data on how it compares with copper, but given the fact that I already have spent the Budget of 70€ (mostly for passives and the Si570), I'm going to use the Aluminium-Foil solution for now.Btw: Is there a way to directly post a link here to a CircuitMaker-Project so you guys can tell me what I'm doing wrong, or is it better to just upload screenshots here?

author: rjeberhardt
author_rank: Regular Contributor
timestamp: October 16, 2015, 02:43:03 pm
content: Quote from: AF6LJ on October 16, 2015, 01:08:39 amWe cobbled some of those up in the 1970s for production line test rigsRussell.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 16, 2015, 05:28:15 pm
content: I hope, this is the link that allows you to view the project-files:http://workspace.circuitmaker.com/projects/114BDE35-CF9F-49AA-95D1-50AE3D481AC5

author: SundayProgrammer
author_rank: Contributor
timestamp: October 16, 2015, 07:30:16 pm
content: Quote from: SaabFAN on October 16, 2015, 05:28:15 pmPerhaps... if you have logon credentials...Axel.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 16, 2015, 07:40:52 pm
content: I think, I ran into yet another problem: As you can see in the attached block-diagram, the FM1216 has no 45Mhz IF-Output and already demodulates the Video-Signal and the Sound.Is it still possible to use this tuner? I'm not sure if I can just take the Video-Signal, convert it down to 10Mhz and then filter it with crystals and measure the RSSI-Output of the SA615.

author: AF6LJ
author_rank: Unknown
timestamp: October 16, 2015, 07:53:32 pm
content: You have your second IF outYou might be able to use that.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 16, 2015, 09:41:17 pm
content: I fear not.According to the datasheet, it puts out a sound-carrier that is designed into the device to provide external stereo-processing or decode additional audio-channels. -.-It seems to me, that this part is too modern/highly integrated for this kind of task^^

author: AF6LJ
author_rank: Unknown
timestamp: October 16, 2015, 09:58:50 pm
content: The next step would be to dig into the module and do some hardware hacking.If you can...I am not acquainted with that module, several here I have you can dig into and hack.

author: PointyOintment
author_rank: Frequent Contributor
timestamp: October 17, 2015, 06:27:18 am
content: Quote from: SaabFAN on September 27, 2015, 05:10:15 pmTHANK YOU!! I saw that page years ago and have been unable to refind it ever since!Quote from: SaabFAN on October 16, 2015, 01:26:12 amI like the improvisation. Looking forward to pictures.

author: marcopolo
author_rank: Regular Contributor
timestamp: October 17, 2015, 10:40:34 am
content: Quote from: SaabFAN on September 29, 2015, 08:55:53 pmMB1501 PLL has a 18-Bit programmable dividerhttp://www.i-biznes.com/datasheets/Fujitsu/MB1501.pdf

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 21, 2015, 12:02:48 am
content: I fear I can't do Filters... I have completely rebuilt the bandpass-Filter, but I still don't see a clear Sine-Wave at the end of it. At least not until I put a Scope-Probe on the output of the Filter. Then I see a Sine-Wave (14pF Scope-Input + unknown amount of capacitance inside the Rigol-Probe) on the scope.Only my Time Domain Reflectometer (74AC14 set up as RC-Oscillator with 5 Outputs in parallel to give 50 Ohms Output-Impedance) was able to produce a rather wide spike on the FFT from about 74 to 82Mhz.I also recognized massive amounts of waveform-distortion when I measured each stage individually with the scope. So much in fact, that the frequency counter showed frequencies way above the 80Mhz I put into the Filter.As you might imagine, I now have quite a few questions- Is Waveform-Distortion in such a Filter normal? If not, could differences in the tuning of the individual stages be the cause?- Is the size of the shielding-box around each filter-stage important?- Is the shape of the waveform at the output of the Filter of importance, or just the amplitude of whatever comes out of it when I send in a specific frequency?This whole Filter-Thing is some kind of a gamebreaker at the moment... If I'm unable to build this Filter, building the rest of this device to develop the software is rather pointless. - My current plan is to build a prototype with about 70Mhz bandwidth on Veroboard to develop the Software and understand the hardware, then remake the thing with better specs (Bandwidth: 0.1Mhz to 225Mhz or even 500Mhz) in Circuitmaker and order some PCBs while trying to keep the "Junkbox-Style".

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 21, 2015, 04:26:23 am
content: Circuit and pictures?

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 21, 2015, 04:11:10 pm
content: Schematic and picture of the Bandpass-Filter. When I don't want to measure anything or fiddle around with the coils, it is covered with aluminium-foil.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 21, 2015, 07:52:44 pm
content: Seems reasonable enough (if messy), just needs alignment I guess? Are your source and load in the proper matched impedance?Mind that resonators coupled with capacitors will give a very shallow hi-end cutoff (asymmetrical cutoff / skirts). Inductive couplings would reduce that, but inductors of very large value are hard to come by (essentially, a value that would resonate with the coupling capacitors in there)Also mind that the tuning will be off when you wrap it with shielding, and it'll be out again when open due to extra coupling between chambers. Better to use deep chambers so the shielding is good already, and have a large distance (several coil diameters) between the top shield/cover and the coils.Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 22, 2015, 04:39:06 pm
content: Well, it seems that the Filter works afterall and I just had the COMPLETELY wrong Frequency-Range: Instead of passing 80Mhz, the Filter is passing 120Mhz. The most likely cause for this is that I probably did something wrong with the coils. I most likely started too early along the copper-wire to count the turns, or measured the diameter incorrectly (I measured outer diameter of the coil)... But it works now, which means that I can continue.The Filter currently has a rather wide band (about 5Mhz), but for now it will be enough, I think.

author: AF6LJ
author_rank: Unknown
timestamp: October 22, 2015, 05:50:06 pm
content: Quote from: SaabFAN on October 22, 2015, 04:39:06 pmGood to see you have it working.A note to file in the back of your mind; when making coils the diameter of the coil form is usually what is specified.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 22, 2015, 06:57:50 pm
content: Use this one:http://hamwaves.com/antennas/inductance.htmlNote the dimensions are wire center, which matters already for small wires, and will be even more important with the wire you've got!Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 05, 2015, 12:42:03 pm
content: Sorry for the slow update-rate here.There is a Workshow at my University next week and I'm polishing up all my projects to make a good impression on the representatives from the Hamburg Gaming-Industry.Once that is done, I'm going to continue with the spectrum analyzer. By that time, the components I ordered (mostly connectors and Coax-Cable to connect the boards) also should have arrived.Btw. has anyone here tried painting RF-Circuits with conductive paint? I find carving the circuit out of copper-plated boards rather difficult.

author: rjeberhardt
author_rank: Regular Contributor
timestamp: November 16, 2015, 07:06:13 pm
content: Quote from: SaabFAN on November 05, 2015, 12:42:03 pmIn principle it should work but you have to take account of the fact that the resistance is much higher than that of copper although it is not as bad at high frequencies as you might expect as the skin depth is greater. I have used silver loaded ink printed on plastic to design a UHF antenna which has been manufactured in large quantity with success.https://www.ryness.co.uk/telecam-tce2000-indoor-tv-aerialHave you tried etching pcbs? It really is easy with photoresist film and computer generated artwork.Russell.

author: AF6LJ
author_rank: Unknown
timestamp: November 16, 2015, 07:52:07 pm
content: Good luck at your workshow.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 16, 2015, 11:09:40 pm
content: Quote from: rjeberhardt on November 16, 2015, 07:06:13 pmI have thought about etching, but haven't tried it yet. Partially because I don't really have the place to safely work with the chemicals involved in that process. It also is so easy and cheap to get boards from China that it is almost not worth trying for most projects. Plus I don't have to drill hundreds of holes into a PCB.But it is on my list, partly because it's possible to create rf-circuits with microstrips, which really interests me. Do you know of a program or a good online-tutorial on how to design these structures to form capacitors and inductors?About the project: I have started to build the final receiving-stage of the analog side: The log Amplifier. It took about 4 weeks for the AD8307 to arrive, but now I have 10 of these ICs. Enough to play around with them and learn how they work and screw up one or two tries@ AF6LJ: Thanks.Here are two pictures of what I showed at the Workshow btw.

author: AF6LJ
author_rank: Unknown
timestamp: November 17, 2015, 03:08:39 am
content: Nice work the lighting is well done.Looks like a scene out of Half-Life.Coolness....

author: rjeberhardt
author_rank: Regular Contributor
timestamp: November 17, 2015, 07:20:14 pm
content: Quote from: SaabFAN on November 16, 2015, 11:09:40 pmThe last time I designe any microstrip circuits I use HPs Touchstone software. That has now evolved into Keysight ADS but is a very expensive package. At the other end of the scale have a look at FILSYN, a free download.Russell.

author: babysitter
author_rank: Frequent Contributor
timestamp: November 19, 2015, 01:23:30 am
content: You might grab a issue of the "UHF-Unterlagen" by Karl Weiner, there you might find design rules for about everything interesting, 80s style. Im tired and have some fever but you seem to want a 80 MHz BPF, i see a cookie box with two BNC connectors and with inductively coupled helical filters inside... the right reason to do itAlso, consider a logarithmic detector like AD8313 (might be totally off by some houndred, see above) to turn a IF level into a voltage.DB6NT published some wide-band VCO designs that you could sweep with a triangle/sawtooth.A old 5 MHz oscope could be used as display.I think in the UFH Unterlage you even find a complete SA design using a old b/w tv set, including turning the deflection coils.

author: tggzzz
author_rank: Super Contributor
timestamp: November 19, 2015, 09:44:49 am
content: I'm going to show my ignorance. No change there, thenFor low power filters in the low hundreds of MHz range, why not use 0603 SMD components? Small values have SRFs in the multi-GHz range.I'd expect a little empirical tweaking might be necessary, just as with any other implementation technology.

author: KJDS
author_rank: Super Contributor
timestamp: November 19, 2015, 11:21:52 am
content: Quote from: tggzzz on November 19, 2015, 09:44:49 amThe bigger the coil*, the better it's Q, the lower the passband loss.*It's a bit of an approximation, but substantially true.

author: tggzzz
author_rank: Super Contributor
timestamp: November 20, 2015, 09:26:30 am
content: Quote from: KJDS on November 19, 2015, 11:21:52 amWhat range of Q might a "large" coil have at those frequencies?A 10nH 0603 Murata LQW18A spec is Q=35@250MHz, SRF=6GHz, R=0.68ohms.A 100nH 0603 Murata LQW18A spec is Q=34@150MHz, SRF=1.8GHz, R=0.11ohms.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 20, 2015, 07:55:45 pm
content: You can pretty easily get a Q over 100 at 100MHz from a small solenoid shape (say under 6mm dia.), and for larger, several hundred, up to one or two thousand for a helical resonator of appropriate size (which might be up to 20cm across!).Tim

author: AF6LJ
author_rank: Unknown
timestamp: November 20, 2015, 08:06:50 pm
content: Quote from: T3sl4co1l on November 20, 2015, 07:55:45 pmBeat me to it; Helical resonators are the Duck's Gutz.

author: rjeberhardt
author_rank: Regular Contributor
timestamp: November 20, 2015, 08:42:57 pm
content: Quote from: tggzzz on November 20, 2015, 09:26:30 amWell, a 10 mm diameter coil consisting of 4 turns of 1 mm wire with a length of 10 mm will give you about 100 nH with a Q of about 750. Make it 20 mm diameter and two turns of 2 mm wire and you get a Q of nearly 2000. A little better than your 0603 inductor!However, you do have to consider the effect of any screening. A bigger coil will need a proportionally greater distance to the screen for the same reduction of inductance.Russell

author: tggzzz
author_rank: Super Contributor
timestamp: November 20, 2015, 08:48:16 pm
content: Thanks; that's indicated yet more things to learn about - helical resonators and the magnitude of the effect of the Q on a filter's characteristics.

author: AF6LJ
author_rank: Unknown
timestamp: November 20, 2015, 08:51:15 pm
content: Quote from: tggzzz on November 20, 2015, 08:48:16 pmThose 1970s ARRL Radio Amateur Handbooks have some useful information.It is a good jumping off point anyway.As a side note.My old HP 8551 spectrum analyzer RF section had Helicals in the 200MHZ IF.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 20, 2015, 10:03:30 pm
content: If you need a very flat, well-behaved response, then you would normally choose a Butterworth filter. But this will have droop in the transition band, due to finite Q. There are filter designs for "constant loss" or "lossy L" conditions. Or you can pick a slightly more aggressive filter, e.g. 1dB Chebyshev, and figure the passband ripple will be attenuated somewhat due to the finite Q, giving something more Butterworth-like.(In the transition region, you necessarily have energy storage, and therefore losses in finite-Q components, and therefore insertion loss. The only way to keep a very sharp filter is to also attenuate the pass band (equalizing insertion loss), or use higher Q (lower loss) components.)If phase response is more important, you'd choose a Bessel anyway (or something near there), which is also less sensitive to losses because of its gradual dropoff (lower filter Q, less stored energy in the transition band). It'll still be a bit droopy due to losses, but the point is, it's supposed to be kind of droopy anyway.Tim

author: rjeberhardt
author_rank: Regular Contributor
timestamp: November 21, 2015, 09:21:09 am
content: I seem to remember that what is needed in the IF filter is not Butterworth, Tchebychev, or Eliptic response but something near a Gaussian response. Something to do with making noise measurements I think?Russell.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 26, 2015, 12:14:30 am
content: Good news: The Filter is finally working (sort-of). I measured it with the scope and a tube-based signal-generator that I got for less than 35€ from ebay.The PM3320 starts triggering on the waveform at about 92Mhz and has the highest amplitude at about 98Mhz (about 3 to 4 times the amplitude compared to the picture at 92Mhz). It then has a rather sharp drop-off and disappears (scope stops triggering) around 102Mhz - Interestingly a frequency where the signal-generator has a massive peak in signal-strength.If I use the sweeperino (assembled on the board I originally intended to hold the spectrum analyzer^^), I get a similar picture: Peak at 98Mhz, fading signal-stregth up to 102 and 92Mhz and for the rest of the frequencies the displayed signal-strength more or less stays the same. Not nearly the bandwidth I wanted, but I guess with this rather non-prescision approach that's probably the best I can get.Interestingly, the Si570 was able to produce frequencies of up to 266Mhz despite the datasheet claiming that 160Mhz would be the maximum.As I dove deeper into the topic of building such a device, I felt that my original specification for a maximum frequency of 225Mhz is kind of limiting, because I'm effectively wasting almost 1Ghz of Bandwidth with the PLLs I bought.I therefore decided to use the first part of the Sweeperino-based SpecAn as the Up-Converter and then put a TV-Tuner Module behind it and essentially copy the PC-Based spectrum Analyzer for the ISA-Bus I linked to in a previous post. If possible I'll use the FM1216 (I hope I can extract the IF by just soldering a coax-cable to the pins of the SAW-Filter inside the module and connect it via the shortest way possible to a buffer-amplifier) or some other type of TV-Tuner

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 05, 2016, 09:10:09 pm
content: Okay, after quite a bit of absence, I'm back on this project.I'm currently trying to get the VCO to work, which I did with varying success: I got the thing to oscillate, but the tuning wasn't quite what I expected.For example, I found 2 maxima over the full tuning-range of 0 to 31V. One at 7V and about 560Mhz and the other one at close to 27V and 810Mhz (I'm planning on using a SAW-Filter with a passband at 434,20Mhz because all my other attempts weren't too successful^^).I built the circuit (the upper one of the two in the attached schematic) on the Vero-Board with the integrated GND-Plane with SMD and through-hole components. Unfortunately, the only device I have to measure this oscillator is a frequency counter, because the PM3320A fails to trigger beyond 400Mhz and the Rigol does trigger but isn't able to display anything useful^^I think the next stage would be to design a PCB for the VCO and build one with only SMD-Components and add some shielding (the current version is VERY dependent on where I sit - Variations of up to 30Mhz up and down). I'm going to buy the boards from a manufacturer here in germany, who is basically just etching copper clad boards. So drilling holes to connect the two ground-planes would be my job... Is there some kind of a rule of thumb how many holes are necessary? Something like 1/2 wavelength for example?Something else: Which oscillator-topology is better? The upper or the lower one?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 06, 2016, 07:05:26 am
content: Well the first one is missing junctions on the emitter, and base bias divider..?Always stagger junctions, so that wire joins meet in tees, not crossings.In the 100s of MHz, you can't meaningfully draw a lumped equivalent schematic. Every trace and pin and wire is stray inductance, with mutual inductance to those around it; and distributed capacitance between them as well. The only way to reduce those couplings, so your schematic is somewhat accurate again, is by building it on ground plane, and probably adding shields around, besides. Since as you've found, it's very sensitive to things nearby, which means there's a lot of radiation (near field or otherwise) streaming off the thing.Note further that equivalent inductance and capacitance is just that, an equivalent. The physical structures are transmission lines -- signals travel at the speed of light (or something near there). Theoretical capacitors and inductors in a schematic are instantaneous, so they cannot truly represent a real circuit. And even that's not a big deal for most things, but when reactances go in circles, paired with transistors that respond well into the GHz...Oscillators aren't hard to make, well, oscillate, but making the tuning range smooth and continuous, and the amplitude stable and the distortion low, is hard, and requires clean construction.Tim

author: AF6LJ
author_rank: Unknown
timestamp: January 06, 2016, 04:03:12 pm
content: One other issue;maintaining reasonably flat output power over an active can be difficult with one transistor.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 07, 2016, 01:41:53 am
content: Building the circuit up on a groundplane is kinda difficult with the components I have (0805 and 0603-Passives, as well as BF420 transistors). That's why I want to get a PCB (double sided copper) with one side etched and the other side untouched except for the vias connecting the top and the bottom side. That's why I was asking if there is a rule of thumb how far apart / how many of those vias are necessary to keep drilling to a minimum.In terms of linearity of the tuning-range, in my experiments the bottom one of the two circuits works better. It also is not so easily disturbed by me moving aroundTo keep the power-level constant, I wanted to use a buffer with a high gain after the oscillator and an attenuator that is controlled by an automatic gain control-circuit, which regulates the amplitude. Or is that unnecessary and I just have to overdrive the Inputs to achieve a Square-Wave at the Input of the Gilbert-Cell? I think I read something about that somewhere, but I'm not sure where and can't find it right now...

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 02:07:47 am
content: Quote from: SaabFAN on January 07, 2016, 01:41:53 amIf you have a signal generator you can build up the mixer and experiment with drive levels.Based on designs I have seen; at your frequency I would think every 5mm or so would be good enough for your vias.As for linearity the old boat-anchor analyzers used shaping circuits to compensate for VCO nonlinearity.It's always good to have more than enough signal level; pads located on critical inputs can go a long way to make up for fussy input stages. The ALC leveler is a good idea. Someplace around here I have a voltage controlled pin diode attunator we use to use in a transmitter we once built back in the 80s. It worked really well, and was easy to set up and tune. It was like a voltage controlled L-Pad and while far from perfect (it introduced a fair amount of VSWR into synthesizer output amplifier) it did the job really well.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 07, 2016, 03:13:20 am
content: Would something like what I attached to this post work?It is the lower of the two circuits (Colpitts-Topology). The size-differences in the +5 Line to the Bias-Resistor R2 is deliberate to form something like an LC-network.Btw. Would it be better to have a Sine-Wave for the Local Oscillator, or would a square-wave be sufficient?

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 04:38:58 am
content: I think that looks good, see what the others say.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 07, 2016, 05:32:59 am
content: In green is your main circuit path, between the caps at the transistor and the varactor at the other end. In purple, the path length is effectively, uh, I'm going to guess a couple of cm. And the impedance isn't very controlled or anything (having everything surrounded by ground does help!), so the fact that that path has physical length, means you've got a transmission line. At very high frequencies, the capacitors look like shorts, and the path looks like a 1/4 or 1/2 wave resonator.FYI, that structure -- having ground poured around microstrip -- is grounded coplanar waveguide. For 62 mil PCB stock, and 10 mil clearance, you get an impedance of about 50 ohms for a 50 mils trace. This is a good calculator:http://chemandy.com/calculators/coplanar-waveguide-with-ground-calculator.htmAlternating between thin traces and relatively wide pads/resistors/capacitors, you get something of a lowpass filter effect, on the order of whatever 1/4 wave of those sections is (so, up in the 10GHz range), and roughly like a transmission line from there until the path length is relevant (~1GHz?), and L or C below that. So, there's plenty of opportunity for that high-falootin' transistor to squeal like a piggy at frequencies you can't even hope to detect...BTW, I like to set a rule so vias connect without thermals. Then you can place them near edges without spokes making a mess of everything.It's also pretty safe to use smaller vias, say 12 mil i.d., 25 mil o.d.Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 07, 2016, 12:23:20 pm
content: So different sizes of traces: BAD unless I want to build combinations of inductors and capacitors.I have redrawn the PCB with that in mind and also eliminated the Thermals from the Vias and all the other components. According to the calculator, the trace-width of 1.5mm with a 0.3mm gap should give an impedance of about 50 Ohms on a 1.5mm thick FR4 board. The RF-Path has a length of about 30mm + about another 10mm from the Emitter to the center of the SMA-Connector.The whole board is 45,5x22,5mm.

author: tggzzz
author_rank: Super Contributor
timestamp: January 07, 2016, 02:29:47 pm
content: Is there any benefit to having a 50ohm transmission line between C2 and Q1 base? Myignorantguess is that ~8mm long line will resonate since it isn't terminated in 50ohms.I'd be tempted to make the line between C2 and Q1 shorter and fatter (~3mm*3mm) by moving R2/R4 up/down and to the left, and possibly removing the ground plane underneath them to minimise capacitance at that node.I'd consider shortening the Q1 emitter track by placing C3 roughly where the Q1 silkscreen legend is.I'd consider adding a decoupling capacitor at R3 to reduce the chance of noise being coupled into the control voltage.You would be unwise to rely on my suggestions - let someone with more experience comment.

author: KJDS
author_rank: Super Contributor
timestamp: January 07, 2016, 03:45:09 pm
content: I would break up R3 into two resistors and use a decoupling capacitor in between. I would add quite a lot of extra decoupling on the supply line, at least a couple of big caps on the supply and something very close to R2I would move R2 and R4 to where the text for them currently is and use a thin line to connect to the transistor base. This allows the tuned circuit to be much closer to the oscillator transistor.Then I would add a buffer amplifier on the oscillator output, probably a single transistor amplifier using the same transistor as you currently have. It costs you an extra cheap transistor, but prevents any pulling issues and saves potential problems if you have something highly resonant on the output.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 07, 2016, 04:05:50 pm
content: Why not put L1, D5 where the "C5" text is?

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 04:39:04 pm
content: There has been enough changes in the design that I have lost track of what range the VCO is suppose to run in.What is the frequency range of the VCO??

author: G0HZU
author_rank: Super Contributor
timestamp: January 07, 2016, 04:40:45 pm
content: Looking at just the circuit, it won't work as a VCO because you have placed inductor L1 directly across the tuning diode. So the effective tuning voltage will always be clamped at 0V DC.It's best to use back to back varactors here as this solves various issues as well as this one.Also your 100k resistor R3 in the VCO tune line will introduce lots of noise once you sort out the first problem above. If your VCO ends up with a gain of about 50MHz/V near the low end of the tuning range then the noise from this resistor alone will mean you will get (terrible) phase noise at about -77dBc/Hz at a 10kHz offset even if you designed the rest of the VCO to be ultra low noise.If the VCO gain was 20MHz/V then the noise will be about -85dBc/Hz at 10kHz offset due to the 100k resistor. This is still quite poor.

author: G0HZU
author_rank: Super Contributor
timestamp: January 07, 2016, 05:09:09 pm
content: Looking at the rest of the circuit the phase noise and frequency tuning range won't be very good. You really want to get lots of group delay in the resonator so this circuit needs to have a high loaded Q. I can't immediately see how you will get a high tuning range but then I'm not sure what tuning range you are aiming for. Also, the value of L1 seems to be quite high at 30nH and the BB429 varactor generally has quite a high capacitance for UHF.I assumed you were trying for something like 460MHz to 850MHz?I haven't analysed your circuit in any depth but it looks like it still needs a fair bit of work at the schematic level.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 07, 2016, 06:59:40 pm
content: The SAW-Filter I have dictates a tuning-range from 430 to 860Mhz to start measuring frequencies at about 100khz. I don't really need to go all the way up to 860Mhz, as the goal was a device that can measure up to 225Mhz (434,20Mhz Filter frequency + 225Mhz Input-Frequency = 659,20Mhz LO-Frequency), but every Hz over that would be niceI have changed the circuit back to the one with the back to back Diodes and the inductor in series with the capacitance presented by the diodes and also added some decoupling-caps (C1, C6 and C7).I have also moved the components back to the more compact arrangement but this time with thicker traces. Not so clean looking anymore, but hopefully better in terms of electrical properties.The tuning voltage available is 0V to 30V, supplied by a DC/DC-Converter (output smoothed by LC-Networks and big capacitors).Btw. the Circuits I got from this website:http://www.qsl.net/va3iul/High_Frequency_VCO_Design_and_Schematics/High_Frequency_VCO_Design_and_Schematics.htmAlso the values of the components aren't final (except for the Transistor). For example I have yet to buy the Varicap-Diodes. Until now I have used leaded BB604B Diodes for my experiments on the vero-board.Edit: Forgot to mention that I added a cutout on the bottom ground-plane, as suggested by tggzzz, to reduce capacitance in that area. Good idea, or not?

author: G0HZU
author_rank: Super Contributor
timestamp: January 08, 2016, 02:36:41 pm
content: QuoteThat was your first mistakeI've seen that dodgy 'va3iul' website before... A lot of the 'designs' on that website are obviously junk. Either that or the bloke who draws the circuits is pissed or high on weed and he makes lots of mistakes when drawing them. I suspect that he likes to imagine and then draw circuits that 'should' (in his opinion) work.However, it only takes someone with a bit of experience to spot that the circuits are often (fatally) flawed. Be afraid... be very afraid

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 08, 2016, 09:30:33 pm
content: Well, I certainly do not have the experienceCan you enlighten me, why these circuits are flawed?The introduction of phase-noise due to resistor-noise I could probably have guessed myself, but how can I eliminate the reistor-noise? Is the splitting of the whole resistance into two resistors (For example 96k and 4.7k) and adding a small capacitor inbetween the two resistors already enough, or would I have to modify the circuit even more? I think the smaller the resistance between the actual LC-Tank and any noise-canceling-cap, the bigger the influence of said capacitor on the LC-Tank, correct?I have added a picture of the circuit with the modifications that I imagined could help eliminating noise, and added some comments to it.Btw.: Although using one of those wouldn't help me learning how to build a VCO, what do you guys think of these ADF4351 Boards available on ebay for just under 40€ from China? Link:http://www.ebay.de/itm/Output-frequency-35M-4-4G-signal-source-development-ADF4351-development-board-/281753222538?hash=item4199ccfd8a:g:WP8AAOSwPcVVq3A~

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 09, 2016, 01:15:39 am
content: It's better to use RFCs than resistors, because inductors don't contribute noise. They do skew the resonant frequency, so you have to use them more carefully.You can't fool noise; noise and bandwidth are always fixed. A capacitor has noise by virtue of the resistance you're measuring it with; the bandwidth is simply the RC cutoff frequency. By filtering a resistor, you still get the larger resistor's noise contribution, but only at low frequencies (which means low frequency / long time period freq/phase noise).As far as how much noise you can actually tolerate, just build stuff. Fix it later. It seems doubtful to me that you'll even have an IF filter nearly tight enough to notice the noise, at least at first. Build a working, simple system, then improve each block until it's instrumentation grade.Tim

author: Yansi
author_rank: Super Contributor
timestamp: January 09, 2016, 12:28:27 pm
content: Hello guys!I am watching this thread quite some time, as it seems very interesting. I'd like to build such thing myself, but I understand this is not thing for a two week build, this is some heavy stuff. So I haven't considered starting such project, as I already have many others under development.But, I'd like to as some questions, about those diy SAs:On theVU2ESE's web pagethere's a statement regarding the Si570:"Unlike a DDS, it has no spurs". Whatta?As far as I know, Si570 is a digital clock PLL synth. That means it should be way worse than DDS boh in terms of phase noise and spurs. It even has a sharp-edge digital clock output! So how can it be "it has no spurs"?So wouldn't it be better to use a sinewave (DDS+filter) oscillator, instead of the digital square wave output of the digital PLL clock synth?

author: G0HZU
author_rank: Super Contributor
timestamp: January 09, 2016, 12:53:39 pm
content: QuoteUmmm... I think it would derail the thread if I did thisMy experience of that website is mainly to do with the homebrew ham radio stuff on the top right of the web page here:http://www.qsl.net/va3iul/There are some real design howlers there.I've not seen the VCO page before and I'm guessing that you based your VCO on the design below.This is shown as a VCO tuning 950-2200MHz. Quite a claim...My first impression of that particular circuit is that it is a bit suspicious. The varactor diode doesn't appear to be rated for 20V use (absolute max is 15V on the datasheet) and I'm also suspicious of the 30nH inductor. This is a very big value of inductance to use here at 2200MHz.A typical SMD inductor that measures 30nH at 950MHz will probably look like 50nH (or higher) at 2200MHz. It could even be self resonant by 2200MHz.So this component is highly suspicious. The increasing inductance with frequency will naturally fight against the tuning meaning it will limit the frequency tuning range because of how it changes inductance with frequency.However, the overall circuit format looks like a UHF oscillator so you could use it as a starting point for use down at 450-850MHz if you modify it accordingly but I think you will struggle to get this much tuning range.Scrolling down the VCO page the 1-1.4GHz Franklin VCO he shows is very bizarre. That definitely looks bad to me. Maybe it does oscillate at 1400MHz but not for the reasons he gives in the text. That circuit looks a real mess to me. But luckily you aren't using itI think you used the circuit below?

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 09, 2016, 03:16:19 pm
content: Yes. That is the circuit I have used.On the vero-board it works with, like I said, the quite unwelcome "feature" of having 2 Maxima (7V and 26V) over the tuning-range of 0V - 30V.I guess this is because building it on the vero-board (with Ground-Plane) with a mix of SMD and through-hole components introduces so many parasitic effects that it actually is interesting that it works at allOther topologies from that website I tried on the vero-board, which worked rather well (mostly linear response to the tuning-voltage, but limited by the transistor to just above 600Mhz - I used a SS9018), were the Parallel tuned Colpitts and the Clapp-VCO (the first and the second one).I haven't tried those with the BF420 yet though.For further inspiration, I have also taken a look at this one:http://www.changpuak.ch/electronics/VCO-1648.phpwhich uses a MC100EL1648DG as the active component. The used IC in that circuit is a bit too expensive in my opinion though: about 10€ from Digikey and over 20€ on ebay! Add the cost for the PCB and I'm in the price-are of the 4Ghz programmable ADF4351 VCO-BoardsThat circuit uses 2 Varactors in parallel with rather small capacitance-values and quite large inductors.

author: KJDS
author_rank: Super Contributor
timestamp: January 09, 2016, 05:29:02 pm
content: Have a look fr the service manual for the Marconi 2382 spectrum analyzer. This was a high performance 400MHz analyzer and use the first LO from that as inspiration.

author: Yansi
author_rank: Super Contributor
timestamp: January 09, 2016, 06:13:32 pm
content: Noone'd like to explain me "spur free Si570 unlike DDS"?

author: KJDS
author_rank: Super Contributor
timestamp: January 09, 2016, 07:10:07 pm
content: Further to my earlier reply, P473 here has the oscillator schematic.http://www.ko4bb.com/manuals/5.66.229.22/Marconi_2382_Spectrum_Analyzer_900A_RF_Unit_Service_Mmanual-Vol2-May86.pdfAs far as spurs go, DDS produce more spurs than you can shake a stick at, Whilst it's possible to get them down to a reasonable level, 12 bits in a perfect world should keep spurs below -72dBc, that's a decent D/A at 800MHz. I'd be comfortable enough with a standard synth being far better than that. There are other issues too, the phase noise of a DDS is a straight multiple of the reference oscillator, whereas a PLL gives the best of the reference close in and the VCO further out. It's a subject that I am far from an expert in, and it really deserves its own thread.

author: Yansi
author_rank: Super Contributor
timestamp: January 09, 2016, 07:24:58 pm
content: Are you talking about a DDS without output filter? Otherwise I really don't get it.Where is the harmonic content of square digital clock from Si570 filtered, that it can be labeled as "spur free"?I really don't get it, how a square wave output can be labeled "spur free", compared to a DDS approach using a lowpass filter, where the harmonic content will be obviously lower.Or maybe I don't know what a "spur" is.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 09, 2016, 08:34:28 pm
content: The idea of looking at the service-manuals of test-equipment was a good one. Thx for that. Completely forgot that the service-manuals of old equipment did include the full schematics instead of block-diagramsAfter some further research, including looking at the pretty interesting Marconi VCO and the ones Philips used in their PM5390 (Hartley-Topology if I'm not mistaken), I found a rather easy to understand and implement one from Infineon. Complete with Board-Layout suggestions and everything. Link:http://www.infineon.com/dgdl/AN061.pdf?fileId=db3a30431400ef68011426c13f560683What do you guys think of that circuit?

author: KJDS
author_rank: Super Contributor
timestamp: January 09, 2016, 10:47:13 pm
content: Quote from: SaabFAN on January 09, 2016, 08:34:28 pmI'd be far happier if they had put just a little theory into the paper. Just a little plot of the analysis showing 1/S11 looking from the resonator into the base, and the corresponding plot of S11 looking the other way.A little mention of Leeson's equation, what's important within it and how their transistor helps provide the low phase noise and how close the performance is to theory. Surely they are trying to sell their transistor for use in oscillator circuits. It is a basic fundamental of marketing that you don't tell, you show. It would have been simple rather than tell us it achieves low phase noise to show us not only that the managed X in terms of performance, but the theoretical best with a 0dB noise figure device would only have been YdB better, therefore our device is great.So what they've done is ok, but it's about as good as the average hotel breakfast, it's a reasonable way of starting the day but with an extra side of paper they could have given us lunch and dinner as well. ... or perhaps they couldn't, either because the device isn't that great or they don't either understand oscillators or marketing. The determination of which it was is left as an exercise for the student.Time for bed said Zebedee

author: G0HZU
author_rank: Super Contributor
timestamp: January 10, 2016, 02:03:15 pm
content: Quote from: SaabFAN on January 09, 2016, 08:34:28 pmObviously, that's only a narrowband VCO up at 2.4GHz but the PCB layout looks reasonable if you wanted to swap a few component values to make something work at lower frequencies. I would prefer to see a tighter layout for a wideband VCO, however.I do have quite a bit of experience of wideband VCO design but it is all quite dated. I was looking at this stuff back in the early 1990s. Today, the components are better, the simulators are better, the knowledge is better. But we stopped making our own VCOs at work over 15 years ago so I'm out of touch when it comes to modern VCO design. The NRE costs and the technical risks are too high so we made a company wide decision to just buy VCOs from Zcomm or Minicircuits etc.I mentioned a bit about this in this old thread here:https://www.eevblog.com/forum/projects/uhf-oscillator/You can also see why I'm reluctant to get too involved in your thread because most of my contribution in that thread was wasted. I designed a 400-600MHz Hartley VCO to show the OP in that thread (probably still got it somewhere) and it met all the specs I listed on that web page. But the thread had already died.

author: AF6LJ
author_rank: Unknown
timestamp: January 10, 2016, 05:51:24 pm
content: I remember that thread, I just watched.......Wideband VCO design is tough.I've had my quota of tuning S and L band VCOs back in the eighties.It was fun to a point.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 15, 2016, 01:03:42 am
content: Well... I can't get any VCO-Topology to work reliably on the Vero-Board.The best result came from this one:http://www.onsemi.com/pub_link/Collateral/ANDSVC704_1-D.PDFand the frequency still jumped up and down.Also with the BFP420 transistor, even that circuit showed the effect of 2 maxima. Not as strong as the other topologies I tried so far, but still noticeable. This didn't happen with the SS9018-transistor though. Probably because that transistor has a much lower fT.Since it seems I have to order boards anyway, I've decided to take the following approach: Put several VCO-Designs onto a piece of PCB and make them at least partially modular and also put the circuit for the ADF4351 Chip on that PCB in case the VCOs do not behave the way they should.Over the weekend I will turn the schematics into board-layouts and post them here before I order them some time next week. It should take about 3 weeks for the boards to get here from china.If possible I'm going to put the PLL-Chip onto that board too in a fashion that I choose which VCO it is going to control.If that isn't working, how should the tuning-voltage be supplied to the VCO? Coax-Cable with SMA or BNC-Connectors, or is a short shielded cable (USB-Cable for example) from the PLL-Chip to the enclosed VCO enough?Also: Would it be better to use a separate can for the PLL-Chip, or can it sit inside the same can as the VCO?

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 24, 2016, 01:40:08 am
content: Okay, I have most of the VCOs on the PCB-Layout now.I've chosen a Vackar-Type, a Colpitts with back to back-Diodes and one based on the Max2620 (just copied the example from the datasheet).The 3 VCOs have SMA-Output Connectors and send their signal to the Input-Board where a BGA2869-Based amplifier is located.The Varactor I've chosen is a BB135, the transistor is still the BFP420.I've dropped the idea of putting the necessary footprint of a fully integrated Frequency Synthesizer on that board because these QFN-Packages are just a pain to solder without a stencil to apply the solder paste.To test these VCOs, I plan to populate only one VCO on 3 of the 10 boards (minimal order quantity at ShenZhen2U) and measure them with the DVB-T Stick I have hooked up to my PC.Btw. not visible on the 3D-View, but there in the outline-layer, is a large cutout that will allow me to easily separate the VCO-Part of the PCB from the rest, where I will fit as much of the Input-Circuitry as possible.Little Side-Note btw: I grabbed one of these Noise-Sources on ebay (the one's that get pretty hot^^) and just for fun measured the Bandpass-Filter I built earlier with the DVB-T Stick.It showed me a passband about 30 to 40Mhz wide (not very flat) at about 460Mhz.I had been aiming for about 100MhzPS: Yes, I forgot to add the Pin-Header for the +5V-Rail when I took the screenshots. They are in there now

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 24, 2016, 01:52:13 am
content: Hi,I think you need to look at L2 and L3. You have 470uH you might want to use 470nH. The concern is that the self resonant frequency of the 470 uH might be too low and therefore act like a capacitor at the frequency you are operating at.Regards,Jay_Diddy_B

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 24, 2016, 03:50:33 am
content: Would Ferrite-Beads work here too?EDIT: I just read a bit about Ferrite Beads and their behavior - They also tend to become capacitive at high frequency.What would happen once the inductors become capacitive? Would this cause a load on the LC-Tank and dampen the oscillation?

author: G0HZU
author_rank: Super Contributor
timestamp: January 24, 2016, 12:43:33 pm
content: Like I said, the circuits on the VA3IUL webpage are often just fantasy circuits. His version of the Vackar VCO (that you are now working with) is just another example.He describes this 600-1200MHz VCO (shown below) as a winner in terms of low phase noise etc but his version is junk. It probably has a VCO tuning gain of over 120MHz/V and a 100k steering resistor so the phase noise is likely to be something like -70dBc/Hz at 10kHz offset.i.e. about 25-30dB worse than a typical VCO design. Some winnerThat's assuming it actually oscillates which is doubtful with a 47pF shunt capacitor in the feedback path. You would only need a tiny amount of package and layout inductance to create an effective RF short circuit somewhere in band with such a large capacitor value and this would mess up the gain and phase. So I can't see how that circuit would be realisable as drawn. I haven't looked at this circuit beyond this.My advice would be to read up on how oscillators are designed and use either a Colpitts or Clapp oscillator. You can get a basic starting point for analysis using an open loop approach or you can analyse it as a negative resistance oscillator. Maybe start off designing a fixed oscillator with no varactor just to make sure you can make it oscillate where your simulation predicts.Even with just a casual glance I can see issues with your latest circuits that question how much tuning range you will get. A simulator will help you predict the tuning range and if you do a few simple sums you can also predict the phase noise performance reasonably accurately

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 24, 2016, 07:31:09 pm
content: Somehow the circuits from that guy are almost unavoidable... When I google for VCOs, they always pop up^^I found another one though. It uses a Pi-Feedback Network and works rather well for the guy who posted the schematic on the german Forum Mikrocontroller.net. He built his VCO, which goes up to 1.2Ghz, on Veroboard with copper-foil glued to the backside btw. A technique I'm certainly going to try^^I managed to fit the additional oscillator into the PCB-Space available on the board and also added the power-supply connections and decoupling-caps. I've also left the Vackar-Oscillator on the board to measure it's performance and post it here - if it is working at all.Is there a book on this topic you can recommend (which doesn't cost 169€^^)?At the moment I have "Halbleiter Schaltungstechnik" by Ulrich Tietze and Christoph Schenk from the early/mid-80s, a book about PLLs (also from the 80s) and my father has loads of material about Audio-Circuits. But except for a few PDFs from Minicircuits about Oscillators and Microstrip-Construction Techniques, we have nothing RF-Related here.

author: G0HZU
author_rank: Super Contributor
timestamp: January 24, 2016, 08:25:12 pm
content: That latest VCO looks like it will have a wide tuning range although I would question how much gain margin it has. This is because of the 470R load in the collector and the resistive nature of the emitter circuit. My guess is that the loop gain will be affected quite a bit by the value of the load resistance presented to it at the output connector J3. I'd also be concerned about the amplitude of the RF signal at D6 at low tune voltages. If the RF amplitude gets big here it may cause issues with D6 at low Vtune voltages.I think it will probably deliver reasonable phase noise and stability as long as it proves to have enough gain margin to start up reliably and if the PCB layout is decent. At some point I would change the 10k resistor R18 to an RF choke in series with a 120R resistor to minimise phase noise due to the steering resistance."Oscillator Design and Computer Simulation" by Rhea (1995) is an old book that now gets bundled for free with some RF CAD SW I have here. It's 20 years old but worth a read. Try skimming through chapter 2 first and then maybe read the book in more detail. It isn't the best book on oscillator design by any means but it is written with a heavy emphasis on (small signal) simulation and this gives a good starting point.I strongly suspect you will be able to download this book for free on the web as a pdf if you do a few searches. If you fail to find it then PM me and I'll email the free bundled version to you. Please can no one else PM me thoughif anyone wants this book then they will be able to get it for free if they search hard enoughThere are lots of newer books (including one by the same author) that go into much more depth but you may find these to be harder to follow etc.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 24, 2016, 10:33:10 pm
content: Hi,I don't know if SaabFan is into SPICE Modelling, but I have put an LTspice model together for the latest VCO.I have included the modification proposed by G0HZU and added an output buffer.This is the model:The results in the time domain:FFT analysis:This shows the VCO operating from around 300MHz (1V) to 900 MHz (31V).I have little practical experience with modelling RF circuit in SPICE. I know a reasonable amount regarding SPICE in general. I obtained the models for the BB439 and the BFR93A by Google searches.I have attached the LTspice file (.asc)Regards,Jay_Diddy_B

author: monkeybro76
author_rank: Newbie
timestamp: January 28, 2016, 05:46:10 am
content: Nice Project! (Y)Jeff.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 29, 2016, 02:23:13 am
content: Well, I managed to build the oscillator on the veroboard using the construction-method described above (glueing copper-foil to the back-side and solder all the ground-leads onto the copper-foil).Testing it, I discovered that the frequency-counter from ebay seems to have issues detecting the right component of the signal. I realized this when I measured the oscillator with the SDR-Stick and saw a rather clean looking spectrum that moved in the right direction when I changed the tuning-voltage instead of jumping up and down.In certain areas the counter was able to lock onto the frequency however and showed me a quite stable frequency - Tuning-Voltage came from my Korad PSU, frequency was stable down to 10s or Hz.For building the oscillator, I used the BFP420 transistor, because it's easier to work with their package, as well as a mix of SMD and leaded components (I only have leaded capacitors with low pF capacities at the moment). Varactors: Axial leaded BB609B. Also the values are mostly not what they were in the schematic because I just used what was available inside the part-boxes.The tuning-range available is about 445Mhz to 740Mhz with the power dropping at both ends of the range. Tuning-voltage: 1V to 29V (maximum Rating of the Diodes: 30V).I haven't made any screenshots yet because it was getting late and I just wanted to check if it is working now, but as I said: The results are promisingTomorrow I'll post a few measurements. Unfortunately the SDR-Stick sweeps really slow, so it takes rather long to take the measurements.Another question came up when I took a closer look at the noise-source: Basically all around the RF-Path the ground-plane has been moved away from the central RF-trace. Why did they do that? Is it because the caps and resistors are effectively increasing the thickness of the trace and they have to move the ground-plane accordingly to keep the 50Ohm impedance?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 29, 2016, 04:40:57 am
content: Quote from: SaabFAN on January 29, 2016, 02:23:13 amHeh... silliness of the design/layout engineer.The most common PCB impedance calculators are for microstrip: a top trace, over a dielectric (with air above, so the dielectric is inhomogeneous), with ground below (usually an inner layer, otherwise things get messy).There is also what's called coplanar waveguide with ground,http://chemandy.com/calculators/coplanar-waveguide-with-ground-calculator.htmwhich is the same thing but with ground pour around the trace.This gives a lower impedance, but calculators aren't as common, appnotes rarely talk about it, the extra copper means more to route or stitch or whatever... etc.But as you can see, these tools are available, so no, there probably isn't any reason.That said... the trace and pad width for the SMT components may be a limiting factor, i.e., you can't make them narrower unless you use prohibitively small parts (harder to hand assemble; limiting on power and frequency range?), and maybe pulling back the ground gives enough margin to keep impedances constant.Not that controlled impedance is much of a concern for modest mismatch (< 2:1) and short lengths (< 1/10 lambda), if that's relevant to the product in question.Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: January 31, 2016, 03:16:26 pm
content: Okay, I have decided to go with the "Pi-Feedback"-VCO (haven't got a better name^^) .Built on the vero-board, it is quite sensitive to movement, so I put Pads on the PCB for a shielding-can.I also added a local Power Supply just for the VCO to eliminate noise introduced by the rest of the deviceWould you say that this thing can work with this layout? Or is there an obvious flaw in it that would mess up the performance?C10 and C12 are Tantalum Capacitors, which I try to fit into almost all of my designs, because I have 2 full reels of themImprovements I just thought about while writing this post (idk. if they are really necessary though):- Separate Power-Supply traces for the oscillator and the Buffer-Amplifier instead - Currently the Base of the Oscillator-Transistor (Q3) is DC-Biased via the same trace that also supplies Q4.- Move the VCO-Supply trace to make it shorter and maybe add an RF-Choke to filter out any noise introduced by crossing the output-trace (Would reducing the width of a portion of the trace to 0,254mm and adding in a serpentine have a similar effect btw.? In the bottom left corner is a little bit of space to do that.)- Make the shielding-pads larger so there is a continuous area where the shield can be soldered to- Move the PSU and J10 around a bit to achieve a 5cm X 5cm board-size (Current size: 5cm x 5,8cm) - Saves 2€ manufacturing cost

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 31, 2016, 07:48:16 pm
content: FYI, you can select the designators (or select the components and select the designators with the link in the Inspector) and reduce their font size; 30 height x 6 width is very common, and will fit much better. With a layout that tight, you'll inevitably have to push them around by hand, probably leaving some off to the side (draw a line from text to part to indicate the relationship, or arrange them in the same pattern as the parts and draw a box around both to indicate matching by relative location).Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: February 16, 2016, 01:23:31 am
content: Little update here before this thread gets pushed back too far by new stuffSo far this project has been a very interesting learning-experience and I'm sure it'll continue to be.I am currently designing the analog board and about to order the VCO-Boards.A little bump I've run into at the moment is the fact that the PLLs only offer rather large frequency-steps, requiring some kind of additional stage to get a finer resolution.So far a third IF with a Si5351 and an FPGA-Based FFT-Solution with a MS/s-Range ADC come to mind. The FPGA-Solution seems to be the much more capable one, but the Third IF is probably easier done.One thing I can say for sure though: It would have been much easier and faster to just build an Up-Converter and slap it in front of a SDR-Stick, let it be controlled by a Raspberry Pi, put everything inside a Box with an LCD-Screen and install the necessary Software.But that would have been rather boring. Building something from scratch is much more fun!

author: SaabFAN
author_rank: Frequent Contributor
timestamp: February 22, 2016, 02:58:35 am
content: So far the analog board is coming together rather nicely.I am designing it in a way that it is possible to upgrade it to higher frequencies by using different components.At first I had the idea of using a stripline-filter as the Input LPF, but that proved to be too large in terms of board-space (was a fun learning experience though^^).Because I couldn't decide how to do the small bandwidth in the end, I decided to put all the acquisition-stuff (where the analog signal is moved to the digital domain) on a different board and put out an If centered at 10Mhz which is filtered with a Lowpass that has a cutoff-frequency of 20Mhz.In my understanding, this should allowa third LO on the acquisition-board to sweep from 10Mhz to 20Mhz, making larger frequency-steps in the first LO (I switched to a ADF4118, doing 20khz steps instead of a TSA5055 capable of only 100khz steps - The ADF4118 also has probably less noise) possible while maintaining a small resolution bandwidth.For a later upgrade, I can simply switch the acquisition-board with one that has a fast ADC on it, and do the last conversion in an FPGA or some other fast digital processor.For the PowerSupply, I opted for something truly out of the junkbox (the rest is looking more and more non junkbox-like^^): A 2x 18V@1.2A Linear Power Supply wih massive heatsink and a heavy transformer, made by Schroff and designed to fit inside the Schroff-Case I'm using to house the Analyzer.One of these two power-rails will supply the RF-Board, the other one is going to provide power for the Acquisition-Board and the Digital circuits, as well as the Display (5inch TFT controlled by a readily available board, both from Adafruit). With enough decoupling, the noise from the digital circuits in the supply on the acquisition-board should be small enough to be negligible.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: March 05, 2016, 06:18:21 pm
content: This is the current state of the Input Attenuator and the first converter-Stage (without the Bandpass-Filter, which is located to the right, out of the picture). If I haven't goofed up the power-calculations, I should be able to feed up to 30dBm into this input-stage.The 74AC14 chips (can be replaced by any CMOS-Logic that can go down to 0,2V Vout-LOW) convert the control-signals from the PCF8574 to switch the attenuators on and off.There's also an output to signal the processor that the input-power is too low and an attenuator can be switched off (I had one OpAmp and one Inverter-Gate left over^^).Note: I just realised that this configuration WILL oscillate and go crazy!So there's going to be an Edge-Triggered FlipFlop in the circuit that holds the Overload-Line high until the processor resets it. An alternative would be to use the LowPower-Sense OpAmp as a comparator with high hysteresis.Aside from that, would this work or is there something terribly wrong?Btw. some of the values are TBD because I'm not sure about the actual performance of some parts - That SMMBD770T1G diode for example.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: March 12, 2016, 09:20:33 pm
content: The VCO-Boards have arrived.I have all the parts, except the Varicaps, so you can expect some test-reports in the coming week (smoke/no-smoke, tuning-range within the limitations of my equipment, etc.).Here are the pictures:

author: AF6LJ
author_rank: Unknown
timestamp: March 13, 2016, 03:21:55 pm
content: Looks good.I am looking forward to seeing how this turns out.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: March 20, 2016, 02:11:56 am
content: Update on the VCO:Unfortunately, I've managed to goof up the footprint for the 2 LM317LZ (OUT and IN were switched because I didn't verify the footprint). So no local supply-regulation -.-Because I didn't have all the specified components on hand, I've chosen a few different values and parts (see the attached schematic) and mounted a PCB-Edge SMA-Connector.Performance-Wise, the results have not been very encouraging. The VCO does oscillate, but it either does so over a rather limited frequency range, or my equipment (RTL-SDR Stick) is simply not able to detect the oscillation because it is too fast. The frequency-counter shows almost always frequencies above 2Ghz.I suspect the Varicap-Diodes to be the culprit here - I put them in a VCO I bought on ebay and it stopped working at tuning-voltages below 9V while the maximum frequency increased by about 200Mhz.With a 39nH inductor, my VCO-Board was a bit more cooperative, but the limited tuning-range I was able to observe was way too low.Btw.: If someone wants to look at the VCO with some proper Test-Equipment, I have 1 fully populated board and 6 unpopulated boards that I could give away (Send me a PM if you're interested).On the RF-Board for the spectrum Analyzer I think I will go with Plan B now: Off the shelf modules from Minicircuits or PLLs with integrated VCOs from Analog Devices.

author: AF6LJ
author_rank: Unknown
timestamp: March 20, 2016, 02:43:38 am
content: Good to see you are making progress, hang in there.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: March 20, 2016, 04:57:23 pm
content: I've attempted to reverse-engineer the VCO I got from ebay.It also has a PI-Shaped feedback-network, but uses a SOT-86 packaged active device - most likely a MMIC like the MSA-0486 I have in my parts-box.With the BB833-Varicap Diodes, it works from 0V (a little less than 700Mhz) to 7.5V (about 1.4Ghz). In its original configuration with BB135 Varicaps, the frequency-range was 515 to 1150Mhz with a tuning-voltage from 1 to 12V.Which makes me think that there is something wrong with the resistor-values in my circuit, which reduces the amplification of the first stage so much that parasitic effects are dampening the oscillation too much.Or it is simply oscillating at such high frequencies that I just cannot detect it and I'm chasing a nonexistent fault.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: March 20, 2016, 10:38:37 pm
content: I've just made a video of me testing the VCO with a few changes to the resistor-values:https://youtu.be/QjycrTTXoUIAs you can see, the frequency-counter is pretty stable around a low tuning-voltage, but shows a frequency way outside the range of my equipment to measure the performance.So far, this has been the best performance I've seen of the VCO. Before, the displayed frequency was all over the place or just 0.In the attached schematic you can see the updated values. R1 had been replaced with a solder-blob.

author: G0HZU
author_rank: Super Contributor
timestamp: March 22, 2016, 11:37:55 pm
content: Speaking from experience, a fairly decent broadband VCO covering maybe 500-800MHz should be able to achieve short term stability of about 20kHz drift per minute once it's been allowed to warm up. So on a counter, you should only see it jump around by a kHz or so from count to count assuming the gate time is in the ballpark of a few hundred milliseconds.Obviously you have to provide a clean and stable tuning voltage because the VCO may have something like 25MHz/V gain.You will need this level of performance as a minimum if you want to make a basic old school swept analyser with a classic free running VCO as the first LO because you will need the display to remain stable (in frequency response) on narrow spans of 50kHz or less. If you plan to use a PLL system then it doesn't matter as much.I think you should try to achieve better than -90dBc/Hz phase noise at 10kHz offset and -110dBc/Hz at 100kHz offset. However, it should be possible to improve on this by about 10-15dB or so even with a homebrew design. The alternative is to buy something from Minicircuits or Zcomm

author: SaabFAN
author_rank: Frequent Contributor
timestamp: March 23, 2016, 02:13:02 am
content: I've planned to use PLLs on every part of the system and use the first LO to do a coarse sweep of the frequency and then use the third LO for a fine sweep of a 5Mhz "channel".If I understood it correctly, that's how Marconi and HP did it in the 80s.The problem I'm having with the VCOs is that the frequency-counter either is counting a harmonic frequency, or the oscillator is really oscillating in the 2.4Ghz-Range. The fact that I cannot see any spikes on the SDR-Stick suggests that the counter seems to be right.If I put the 39nH inductor into the circuit, the counter seems to cannot find the correct frequency and the SDR-Stick shows quite a few spikes but none that really stands out, plus a lot of noise starting at 1.5Ghz.It's really annoying to not have the equipment to measure these things - For example a frequency counter that has only 2 buttons and comes without a manual.Which is why I've decided to use components that have been tested and are ready to use. Like modules from Minicircuits - I already have a ROS-1700W, which I'm definitely going to use.For the first LO I'm most likely going with a ADF4351, because it's really small and contains everything. The QFN-Package is annoying, but I've managed to solder those evil bastards in another project already with rather good results.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: April 25, 2016, 01:19:03 am
content: Quick update here: This is the state of the Analog Frontend-Board. I've gone back and forth on the design of several areas quite a few times, but I'm getting closer to the finish-line.As I announced, I chose an ADF4351 integrated PLL + VCO, because the VCO I built earlier didn't perform as expected (doesn't mean I'm giving up on building a VCO, I just want this project to be finished on the Hardware-Side). The second LO is provided by a ROS-1700W+ I got on ebay a few weeks ago and is controlled by a TSA5055 PLL, of which I'm planning to use the GPIO-Pins to replace one of the PFC8574.What's finished?- Power Supply- 1st LO- Input-Attenuators- Signal-Path up to the output of the BPFToDo:- 2nd LO (won't require an AGC, because the frequency is known and therefore the RF-Power - About 8dBm according to the datasheet)- Input-Protection (I have a few ideas - I want 2 protection-levels: Hard-Protect (All Attenuators are turned on + maybe a dummy-load, preventing a very strong signal from frying the first amp and the attenuators. This happens regardless of Attenuators-Settings, because the attenuators are OR-Connected to the control-signals and the Protect-Signal / Soft-Protect: The Software receives a warning that the input-power exceeds -25dBm and input-attenuators have to be turned on to prevent damaging the components next in the signal-path - Doing this requires measuring the RF-Power over the entire frequency-span (10kHz to 1.5Ghz -The stepped Impedance LPF will have the 3dB-Point at about 1.3Ghz). Maybe the answer is staring me in the face, but at the moment I can't see it^^- Interface-Connector to the Processor-Board- PCB-Layout and defining of shielded areasDropbox-Link for the schematic (XPS-File):https://www.dropbox.com/s/9orliq8cbo4okz8/Analog%20Frontend%20-%20Preview%2001.zip?dl=0

author: AF6LJ
author_rank: Unknown
timestamp: April 25, 2016, 02:28:27 am
content: Looks like you are making good progress.

author: KJDS
author_rank: Super Contributor
timestamp: April 30, 2016, 11:13:35 pm
content: For the overload protection, either use a limiter on the front end, or else have a simple broadband detector that opens a relay. It's possible to use both as belt and braces.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 04, 2016, 04:56:49 pm
content: After some quite frustrating days involving some Battery-Chargers for sailing-boats (the devices which I wanted to check with the result of this project), I'm finally able to work on the spectrum analyzer again.The idea with the relay is good. I had thought about that before, but was uncertain about possible distortion introduced by the relay.I have quite a few PRME 15505 Reed-Relays here, but no idea how their impedance is at higher frequencies. I guess not too goodHow can I measure the HF-Characteristics (except attenuation - that one is rather obvious^^) of them without a Network Analyzer? I have a broadband noise-source and an RTL-SDR Stick, as well as the VCOs and a simple Square-Wave generator (The simple TDR-Circuit W2AEW showed in one of his Videos) based on a 74AC14, that I can set to 570kHz or 2.4Mhz. Measured rise-time is about 1.5ns. Idk if the circuit is faster or not - My PM3320A has a specified rise-time of 1.75ns.

author: tggzzz
author_rank: Super Contributor
timestamp: June 04, 2016, 07:46:34 pm
content: Quote from: SaabFAN on June 04, 2016, 04:56:49 pmYou have the equipment to indirectly calculate the transition time. FFI, seehttps://entertaininghacks.wordpress.com/2015/08/11/measuring-digital-signal-edge-rates-without-an-oscilloscope/The noise source isn'tnecessary, but can help.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 07, 2016, 03:58:04 pm
content: Well, the relays are pretty much unusable.Up to 300Mhz their behavior is more or less neutral, but then they start to introduce spikes and drops in the spectrum (measured with the noise-source and the SDR-Stick). Especially noticeable is a drop around 1.1Ghz.Instead of the relay, I'm now going to use a HF-Switch from MACOM or Analog Devices to switch between the normal signal-path and a Dummy-Load.Or I'll just put a warning sticker next to the input-connector

author: AF6LJ
author_rank: Unknown
timestamp: June 08, 2016, 02:50:27 pm
content: I would go with the warning sticker, cheaper and requires less design effort.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 08, 2016, 09:50:11 pm
content: Quote from: AF6LJ on June 08, 2016, 02:50:27 pmProbably the best way to do this - HP did this tooI'm currently thinking about how to supply the +33V Control-Voltage for the second LO (The VCO is a ROS-1700W+, the PLL-Chip a TSA5055). My current approach is a MC34063 running at 100kHz and boosting 18V from the Main PSU to about 35V, followed by a LowPass-Filter and an LM317L. An LED set to take 10mA is the constant load to keep the LM317L occupied, and the output is further smoothed with 2 220µF caps.Is that enough to filter out the ripple-voltage created by the MC34063, or should I use a different chip?Btw. A euro-card is probably too small to fit the entire analog frontend. I've already moved the BPF and the 1st LO to a different board (ebay board with an ADF4351 on it), but it's still going to be very crowded. Especially once shielding-cans for the signal-path come into play.Is it necessary btw. to shield all the components (attenuators, 1st Mixer, 2nd Mixer) individually / per function-block, or would a single Can be sufficient?

author: AF6LJ
author_rank: Unknown
timestamp: June 09, 2016, 03:36:24 am
content: Quote from: SaabFAN on June 08, 2016, 09:50:11 pmYou could also get a limiter diode from HP to put on your analyzer to protect it.Those were beefy I have only seen two smoke. One smoked when a tech (who should have known better) put a 40W S-Band into the front end of an HP 8569. The other time was another tech who was not there very long... He ran his Hp audio generator into his analyzer and it didn't like 30V P to P smoked that limiter diode really well. In both cases there was over 2K in damages to both analyzers.QuoteYou are braver than I, I would be very weary of using a switching supply knowing the potential for how difficult it can be to keep the crud out of sensitive circuits sharing a confined space.QuoteThis is done in the better analyzers I know of. It makes it easier to manage when you have nice neat transmission lines and the occasional inline pad.My Two Cents....

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 09, 2016, 10:41:40 am
content: Quote from: AF6LJ on June 09, 2016, 03:36:24 amThat's why I was planning on using LC-Filters with 220µF caps and 47µH Ferrites to filter out any nasty stuff.But putting the switchers on a different board and positioning that on the other side of the case is probably necessary to make the supply really clean.Btw. 33V and the negative 12V are the only voltages for the analog components that are supplied by switching regulators. Everything else is done with linear regulators.

author: AF6LJ
author_rank: Unknown
timestamp: June 09, 2016, 03:56:30 pm
content: Quote from: SaabFAN on June 09, 2016, 10:41:40 amSounds good.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 10, 2016, 01:24:37 am
content: Okay, the schematic for the Analog Frontend is pretty much finished. Values may have to be corrected in some areas (the PLL Loop-Filter of LO2 will most likely require some fine-tuning), but the rest is pretty much done.Unfortunately, I discovered that the Analog Frontend-Board alone will require 2,5A in a worst-condition scenario (for the digital components I used the maximum ratings). A large portion of that current is consumed by the RF-Amplifiers and the VCOs.I've therefore added a +9V rail that will be generated on the PSU-Board by a switching converter and from which I'll get the 5V for the digital and analog circuits, as well as the 5,5V for the power-hungry MMG3007 amps I'm using in the Signal paths of LO1 and LO2.Schematic attached - It is an A0-sized PDF-Document with some glitches and I haven't put the Power-Connector in yet, because I haven't decided which one I want to use (Microfit-Connectors by MOLEX look nice, but Digikey is down atm. and I want to check the price first).

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 10, 2016, 12:04:51 pm
content: Updated schematic:- Added the Power-Connector- Replaced the AMS1117 regulator by a LM317L- Replaced LM7805 for the VCO with a LM317L configured to provide 12,6V (it will dissipate about 500mW of heat, so it's going to be equipped with a Heatsink)

author: AF6LJ
author_rank: Unknown
timestamp: June 12, 2016, 03:26:03 pm
content: Looks Great.Good to see the linear regulators.Keep those updates coming.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 14, 2016, 11:57:48 pm
content: First version of the Block-Diagram for the Aquisition-Board is done.I'm not sure how to implement the selectable bandpass-filter yet, it also may not fit onto the board with so many different ranges, so I've put it as a black box on the Block-Diagram for now.I have again drawn from the block-diagrams of the HP 859x-Series for the aquisition-board, but instead of performing the Video-Filtering and the peak detection in the analog domain, these features will be implemented in software.I also scrapped my original idea of using a parallel ADC with some SRAM attached to it and instead opted for an exclusively serial interface for both boards that goes so far that ONLY i2c and SPI are available, with SPI ChipSelect-Signals and other status-signals generated/received by i2c Port Expanders. It adds a bit of communication-overhead, but also allows a simpler interface to the processor-module.Also by limiting the required data-lines, the range of compatible "Processor-Boards" increases - I was thinking of the Raspberry instead of an Arduino Due here.

author: AF6LJ
author_rank: Unknown
timestamp: June 15, 2016, 02:33:52 am
content: I have only seen the bandpass filters implemented in older analyzers usually using selectable Gaussian filters. I am sure more modern analyzers use some form of DSP to do the filter heavy lifting.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 15, 2016, 07:03:09 am
content: I was thinking about putting the Filters into a DSP, but I have no experience in programming an FPGA.A rather cheap 100MS/s ADC (6€ in single quantity for a 10bit ADC, 3€ for 8bit) is probably enough to sample a 16Mhz final IF, but how many Samples should be taken before the next measurement? 2 full periods oft the lowest possible frequency (11MHz) enough?

author: Yansi
author_rank: Super Contributor
timestamp: June 15, 2016, 10:50:38 am
content: I think modern SAs work as an SDR receivers. Have you thought about sampling the baseband signal and then computing FFT? (or doing really a narrowband signal filter). Both FFT and filtering is available on any decent microcontroler today. But requires programing :-)A decent modern 32bit MCU might have a 12bit ADC up to 10Msps or so (but you know, not the best ADC on earth). Still might be helpful.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 15, 2016, 11:02:33 pm
content: I had been thinking about directly sampling the final IF and performing an FFT on that data basically since I started this project, but then postponed any development in that area because I feared it might be too much when combined with all the new RF-Stuff I had to learn for the 1st and 2nd converter-stage.Do you think it's difficult to pull something like this off? My guess is that an ARM-CPU would struggle quite a bit to handle all the data from a 60MS/s 10bit ADC, so an FPGA-Solution would be necessary.The FPGA would have to handle 2 datastreams simultaneously:- ADC-Data to RAM (a preset number of samples that is large enough to allow analysis of the signal and give the FPGA enough time to perform the necessary calculations on the previous set of samples)- Analysis of ADC-Data and transfer of the results to a place where the processor-board can access it and then combine it with the static elements of the display (Annotations, values, the reference-grid, etc.)A quickly drawn up Block-Diagram would look like this:

author: Yansi
author_rank: Super Contributor
timestamp: June 15, 2016, 11:35:38 pm
content: Why do you think it would struggle? It's all about the number of samples or frequency resolution respectively. I am no DSP/FFT expert here, but if for example 60Msa/s data in a 4K long buffer will yield fs/N = 14,65kHz resolution per FFT bin. Imagine the device you want to display the whole spectrum. It would not even have enough pixels to display it natively, a scale down have to be made. And let me tell ya, the MCU will spend more time scaling down and drawing than computing the FFT. If I remember right, 4Kpoint FFT in float32 on Cortex M4 using the CMSIS DSP lib was something slightly above 4 miliseconds (but don't remember the CPU clock... maybe 120MHz?). I wouldn't call that a struggle.If more resolution needed, what's te problem of sampling more than 4K buffer? I don't have any FFT performance data for Cortex Mx MCUs for hires FFT sizes, but I think if you can let it compute for a whole 1 second, you can calculate one hell of a long FFT. (would be actually interesting to see, how big FFT can CM4 do in a 1 second time period, huh?) I think 1 second sweep for hires mode is still very usable.Only a small cheap CPLD like Altera MAX II to help with fast data acquisition (ADC+CPLD+SRAM), connected to an external MCU bus for fast data transfers... If you choose some grunty Cortex M4 MCU, you can also advantage from an integrated SDRAM and LCD TFT controller for faster processing and drawing. (for example STM32F429).I think it is very much doable, but please tell me if I am wrong.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 17, 2016, 12:17:54 am
content: I don't know... Based on my experience with FFT-Functions in my scopes, I figured that it's rather costly in terms of processor-power and doing a full sweep (10kHz up to 1,5GHz - probably even more if I can make the Input LPF sharp enough) with at least 150FFT results that have to be calculated and then stitched together seemed like quite a big task for a small embedded processor.But I have absolutely no experience when it comes to implement FFTs and haven't really looked at the math involved - I just started reading a book about Digital Signal Processing to get to know this stuff.But based on your description it seems to be doable in Software with a CPU and some glue-logic. I think, I'll try to make some kind of test-system on the breadboard with my Arduino DueTo be on the safe side, if FFT on the CPU turns out to be too slow, I'll keep the analog aquisition board, but reduce the available resolution bandwidths to 3 or 4. That way a fast sweep can be made with the analog components to find the area of interest, before switching to FFT-Analysis of that particular part of the spectrum.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 22, 2016, 08:19:38 am
content: After a bit of research, I've decided to build the analog aquisition board first, because I can assemble most of if on vero-board by using stuff flying around on my desk.After that I'll build the FFT-Board on a PCB designed for that.My plan for aquiring and displaying data with the FFT-Board looks like this:2nd IF via Buffer-Amp and Ref-Level Amp into a fast ADC (20MS/s or more) -> ADC-Data via Altera MAX V into one of 2 SRAM-Banks -> Data from SRAM via the same MAX V to DSP (Freescale Kinetis Arm Cortex-M4 - The processor on the Teensy 3.2) -> FFT-Result Output to another SRAM that is then read by the Processor-Module, which combines the Bitmap with the other Display-Content and sends the whole pack to the Display.

author: Yansi
author_rank: Super Contributor
timestamp: June 22, 2016, 11:19:43 am
content: Oh goodness. Forget that piece of junk from Freescale. Look at some manufacturers, that know how to do a Cortex M microcontroller. If I looked correct, the Teensy is 72MHz CM4, it even don't have FPU (floating point hardware)! Please don't mess with this junk.Microcontroller and external self-refreshed LCD is not a good way how to do it fast. You should use a microcontroller with its own memory and LCD controller, so you have a direct access to the display memory. That's why I have suggested using something like STM32F429, which is a quite beefy device running up to 180MHz and has the FPU hardware, that can be used for fast and precise FFT calculations. Comes with SDRAM controller, LCD TFT controller and some basic HW acceleration for bitmaps (clipping, moving, crude resize, color conversion, alpha blending, rectangle filling).Trying combining image within a CPLD - why, if the microcontroller can do it itself, in hardware? In the above mentioned STM32F429, the LCD TFT controller can work in three layers (all by HW): Background solid color and two image layers with alphablending in between. You would only need to pack the whole spectrum on the width of the display, which should not be a hard task.I don't know how much background do you have in programming or how much experience with modern 32bit MCUs, but we are not talking here about "small embedded MCUs" any more, these are the big ones. I just want to point out, if you plan to try the FFT/DSP version of it, do it on proper HW, not some half-assed Freescale junk, which is not suitable in any way here. If you need a pre-built kit to begin with, you can possibly try thisSTM32F429i-DISCOVERY kit. All IOs are available, including the external highspeed bus that could be connected to the CPLD. You could easily produce a custom expansion HW board for the kit, in your case that might be the CPLD and ADC and other fast memory.If you'd like to discuss my weird ideas further, please PM me, I don't want to hijack this topic.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 23, 2016, 02:33:48 am
content: I just updated the Block-Diagram of the entire System.I have added the FFT-Board, based on the STM32F429, as suggested by Yansi, as well as the Arduino-Processor Board, the Front-Panel and a possible Upgrade-Option for a Raspberry-Pi.On the FFT-Board, I have kept the CPLD to sample the data, to offload that task from the processor, so it can dedicate all its cycles to computing FFT and either providing the results for a processor-board, or displaying them directly on a connected LCD. I have found a few LCDs, but most have either HDMI-Connectors or are designed to mate with the Arduino Due / Raspberry. So either an adaptor is needed, or I have to use an Arduino Due as the display-controller that fetches the FFT-Data from the FFT-Module to display it.I've also run an early estimate on the cost of this thing: Just the components and boards are about 350€ for the cheapest version (analog aquisition) and assuming I can sell 4 of the 5 boards minimum order from china.If I add the FFT-Module, that's another 80€.Still about 100€ cheaper than the cheapest HP8591 on ebay

author: AF6LJ
author_rank: Unknown
timestamp: June 23, 2016, 02:44:53 am
content: Very Cool and that is not such a bad price ether.

author: CJay
author_rank: Super Contributor
timestamp: June 23, 2016, 05:43:23 pm
content: Quote from: AF6LJ on June 23, 2016, 02:44:53 amAgreed on that, I'd be interested in building one.

author: Yansi
author_rank: Super Contributor
timestamp: June 23, 2016, 06:54:33 pm
content: I have meant the STM32F429i-DISCO kit only as a learning platform or for development. The chip itself has a builtin LCD TFT controller (refreshing the data periodically from a videomemory/buffer located in the external SDRAM). There is a ton of interesting cheap LCD TFT panels out there, which have the suitable RGB video interface. The RGB interfaces are mostly unified and using such displays requires only connecting the corresponding LCD pins to the integrated LCD driver in the MCU and simple and straightforward configuration of data timing (i.e. screen refresh rate, pixelclock frequency, vertical and horizontal front- and back- porch, sync pulses duration, display resolution). Requiring to copy a set of numbers from LCD datasheet into the peripheral registers in the MCU.By the "ton of LCDs" I mean some cheap pannels mostly from Innolux, available from the common chinese sources. For example the "smaller ones 480x272px": AT043TN13, AT043TN25, or larger VGA (640x480) ones: AT050TN22, AT056TN52, or even larger ones are available (up to 10", 800x600 or 800x480 widescreen).Just for those curious, a common LVDS digital or the standard VGA, DVI or even HDMI displays can be interfaced to these ARM chips with integrated TFT controllers. The resolution achieved won't be high, but there is set of chips that can covert the parallel RGB data to a serial LVDS, analog VGA or differential TMDS data for DVI or HDMI. Not even expensive, in the "few bucks" range.However, the bigger the panel, the larger the data flow through the SDRAM. For realiable and multilayer image operation a 32bit SDRAM is highly recommended (Warning! Nasty highspeed digital bus routing required!) and a 16bit SDRAM is a must anyway for any LCD work.I talk about these things as they are easy, well, I work with these on an almost weekly basis and the complexity might be relative, depending on your previous experience with modern digital design. It is not hard, but requires some effort and learning curve. If you want to try these things, we can help for sure. But be warned and prepared :-)For example: The STM32F429I-DISCO kit (stripped from no more used parts, used only as a MCU+SDRAM board with a debugger) drives an 8" SVGA (800x600) display through LVDS, using a custom made expansion board (as pictured on the LCD).These things are really possible to design at home, none special tools required, except a decent PCB CAD and a soldering iron. You can take this as an example of what is possible, but I'd recommend to better start with something more easy, like running the small on-kit LCD (240x320px, so not so small either) and then advancing to bigger ones with custom digital boards.(Sorry for disrupting the topic again with my digital stuff)

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 23, 2016, 08:58:24 pm
content: Quote from: Yansi on June 23, 2016, 06:54:33 pmNo problem - It actually shows new and interesting ways of doing things for a digital n00b like meStarting small and then continuing with bigger stuff is basically written all over this project - Just look at the title; The upper frequency is now 8 times higher than originally plannedI've already put the Discovery-Kit into my next Digikey-Order, so I can play around with it.Putting the entire Disco-Board on the FFT-Module is my solution to the problem of hand-soldering these fine-pitched packages. Should I decide to do a Kickstarter or there's enough demand that would warrant a small-scale production-run that includes assembly by a board-manufacturer, I'll put the components on the Discovery-Kit on the FFT-Board of course (once I'm confident I can layout a board with fast digital signals on it).About the LCDs: I haven't spent any time yet looking into the matter of how to get the data on screen yet. At the moment I'm focusing on getting a signal from the Input to the ADC as clean as possible.Once I'm done with that, I'll start investigating that topic.Unless someone else wants to jump in here. This thing is Open Source Hardware after all

author: Yansi
author_rank: Super Contributor
timestamp: June 23, 2016, 10:19:24 pm
content: I might just be the opposite - I am an RF n00b, but like to learn :-) I am watching your thread from the beginning, as I am always impressed by any diy SA builds. Mostly this one from S53MV, that is a real beast:http://lea.hamradio.si/~s53mv/spectana/vco.htmlI think you should not do any kickstarter. The market fort this thing is very, very narrow. If you'd like it opensource, it'd be best to make a very detailed project documentation, including explanations, why such circuits were used and why not the others, etc.The above mentioned SA from S53MV is really a great construction, but the documentation is not going deep, it's only mostly a "how to copy" manual. A curious person like me who likes to modify and experiment with stuff can't get much deep understanding, without doing a very detailed reverse engineering (which also requires previous experience, which I don't have and gaining such experience is very difficult).Yan

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 26, 2016, 11:31:39 pm
content: I just realized that I have a major error in my Signal-Path: The 2nd Mixer (ADE-11X) had the 1dB Compression-Point at +1dBm and I wanted to let the 1st IF scream at it at +12dBm. OopsThe Amplifier after the 1st Mixer has been removed now, but there's another problem: I specified the 1st IF to be at 2,1264GHz, but the ADE-11X is only specified in the datasheet up to 2.05GHz. I'm guessing that there will be nasty distortions or at least the conversion loss will become excessively high.Also the curve in the datasheet shows that over the 30MHz bandwidth of the 1st BPF frequency-response is not flat.So I decided to kick the ADE-11X out and put another HMC213 in there. It's about 2€ - 5€ (depending on where they are bought) more expensive than the ADE-11X and can be bought at Digikey, plus a much nicer looking frequency-responseThe analog aquisition-board will be on Euro-Card sized Vero-Board btw., but I'll also do a PCB that can be orderedAbout the Kickstarter and opensourcing this project:You're right. Kickstarter is probably not the best idea.A kit, or just the boards I have left after I built my device, sold on Tindie or eBay is probably better. If I get back the money I spent building this thing (including all the stuff for experiments), that's enough for me. Everything else above that is a bonus.Source-files (Schematics, Board-Layout, Documentation etc.) will be released here and/or on a dedicated blog.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: July 31, 2016, 11:54:41 pm
content: I'm currently a little short on time to really work on this project.I think I have the Analog Frontend done and am now working on the aquisition board whenever University-Assignments and another Project (Half-Bridge Converter with 250W Power-Output to charge Batteries via cheap Solar Charging-Controllers that only regulate the GND-Wires).The status at the moment:- Analog Frontend: Circuit DONE, Layout @ 0%- PreAmp-Board: Idea Only- Aquisition Board: Block-Diagram, Circuit @ 20%- Processor-Board: Block-Diagram- Display/Keyboard-Assembly: Block-Diagram & Parts connected on Breadboard to check functionality of the LCD-Module- Filters:- Input-LowPass: Values Calculated- 1st IF-Bandpass (Microstrip): Values Calculated- 2nd IF-Bandpass: Veroboard-Prototype Done- Final IF-Filter (Narrow Bandwidth): Veroboard-Prototype (Signle Quartz) DONE & Tested- Final IF-Filter (Medium-Bandwidth): Veroboard-Prototype (Ceramic Resonator) DONE & Tested- Final IF-Filter (Wide Bandwidth): Values Calculated- Software: 10% (Libaries imported and checked - Arduino does put out a picture on the Display with the Adafruit Demo-Software)In 3 weeks I'll have a bit more time available, which I hopefully be able to use to build a prototype of the aquisition-board on Veroboard (building microstrip transmission-lines on single-side contacted Veroboard works pretty well so far) and a simple Signal-Generator that can go higher than the Philips PM5190 I have on my bench right now.The Signal-Gen btw. will be some simple thing built out of the Si570-Test board I built right at the beginning of this project. So at least that money finally sees some useAmplitude-Control will be accomplished by a PIN-Diode attenuator that is controlled by a DAC and uses a AD8307 in the Feedback-Loop.The Controller for this will be the Arduino Nano that I damaged with my 8741-Programmer (Analog Inputs 4 and 5 blown when the Multimeter-Probe slipped) - So there will at least some Junkbox-Style construction involved in this whole endeavorI've also bought the Discovery-Kit on ebay - There's currently a sale in Germany of them (STM32F429 Discovery-Kit) for 15€ + 3€ Shipping: Ebay-Link:http://www.ebay.de/itm/361623155657?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT- So I could use a few links about programming this beast, and specifically about FFT-Libraries for it, while sitting on the bus

author: AF6LJ
author_rank: Unknown
timestamp: August 07, 2016, 03:27:18 pm
content: Very Cool...

author: voltz
author_rank: Frequent Contributor
timestamp: August 07, 2016, 08:50:15 pm
content: Regarding your STM disco board programming, there's an interesting thread going on here:https://www.eevblog.com/forum/microcontrollers/so-how-do-you-even-start-working-with-stm32-without-paying-an-arm-and-a-leg/Might help.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: August 13, 2016, 08:34:19 am
content: Thx for the link, I'll check it out over the weekend.Unfortunately, I didn't have much time over the last few weeks to work on this, because I had to learn how to make a DC/DC-Converter with isolated outputs to supply cheap chinese solar-chargers for yet another boat, but on the other hand, I'm soon going to have the money to order the parts and PCBs for the analog board and the first IF-FilterA few words about the 1st IF-Filter:I want to use Microstrip, but except for the analog board, I have no means of measuring something in that frequency-region (2,126GHz). I also only have access to FR4-Boards (anything else would be too expensive), so I think characterizing this Filter is necessary.Would anyone here with the right Test-Equipment be wiling to do something like that? Maybe even make a Video about it and do something like a "Fundamentals Friday"?I'm getting 10 Boards anyway, so I can spare a few.

author: KJDS
author_rank: Super Contributor
timestamp: August 13, 2016, 04:18:30 pm
content: How wide can you let the filter get? hint, the wider it is the lower the lossWhat rejection do you need from it? hint, the less the rejection, the lower the loss from the filter.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 14, 2016, 01:45:31 am
content: Also, the wider the band edges can be, the looser your filter tolerance needs to be, both in terms of Q (which gives lower losses too, as KJDS said) and by mechanical fab tolerances (better chance of getting it right the first time?).Tim

author: AF6LJ
author_rank: Unknown
timestamp: August 21, 2016, 04:39:39 pm
content: This is a great thread.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: August 22, 2016, 02:41:25 am
content: I think a 40 to 60MHz wide Filter for the first IF is good enough.This tool:https://www-users.cs.york.ac.uk/~fisher/cgi-bin/lcfiltershows me 40dB rejection at a frequency of 2070MHz with a 5th Order Chebychev 0,01dB ripple Filter. A 7th or 9th order Filter can provide much better results, but also requires more board-space. I'll have to see how many elements I can fit on a 10x10cm board.Is -40dB enough btw.?The LowPass-Filter at the input will probably have a rejection of 30dB at 2100MHz.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: September 15, 2016, 06:04:42 pm
content: When the Paper for university starts to annoy you, just relax and calculate some Filters instead XDI've done the LC-Filters for the 3Mhz wide and 1MHz wide 10.7Mhz IF-Bandpasses (see attached pictures) and the 2nd IF-Filter. Component-Values are cross-checked with Digikey to ensure there are no hard to find parts.HP used several LC-Poles and crystal-filters in the 8968-Series (the only one I could find Schematics for - rather crappy scans though...), which could be put in series or bypassed to get the selected bandwidth. I chose to do it in an easier fashion: The higher Bandwidths get dedicated Filters and only the lower bandwidths that use crystals will have an arrangement that allows bypassing of filter-stages.The Filter-Steps will be 3MHz, 1MHz (Optional if enough board-space), 300kHz, 100kHz (optional if enough board-space), 3kHz, 1kHz.

author: KJDS
author_rank: Super Contributor
timestamp: September 17, 2016, 08:11:51 pm
content: Am I reading correctly that you've got a 500uH inductor in series with a 700fF capacitor? if so, that's not realizable in practice as the inductor will have far more stray capacitance in it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 18, 2016, 02:17:22 am
content: Series resonant tanks can be transformed to parallel resonant tanks, keeping the coupling coefficient the same (as shown: coupling coefficient is the impedance ratio above or below Zo; it's usually replaced with an inductive coupling coefficient for coupled resonators).Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: September 18, 2016, 07:55:27 am
content: Quote from: KJDS on September 17, 2016, 08:11:51 pmOops. Missed that one. Inductance needs to be much lower while capacitance needs to be much higher, obviously. The 3MHz and the Filter for the second IF had been corrected accordingly.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: September 29, 2016, 11:45:54 pm
content: After struggling a bit with the different filter-types, I have now opted for the same approach HP used: Several Parallel Resonators that can be connected in Series or bypassed.I also found a much more usable software than Filsyn: Elsie by Tonne Software. It has a free student-version that allows up to 7 stages of a filter to be chained together. The Pro-Version can do a lot more.With that software, I was able to design someting I should be able to build over the long weekend (we have a holiday on monday in Germany) and test it.I have also had some thoughts about the Video-Filter: I would like to avoid a complicated network of analog Filters and a solution that I had in mind involves a 3MS/s 12bit ADC connected to a SAMD21 Micro (which I have somewhere in my Parts-Drawer^^) that receives the data from the ADC, integrates the readings according to the setting selected and puts out the current value on 12pins. Running at 48MHz, I think it should have enough computing-power to do the necessary calculations during the short time period the ADC needs to get a reading.Not very elegant, I know, but it is easy to implement and there's nothing else for this chip to do here

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 21, 2016, 06:13:13 pm
content: Circuit-design of the analog aquisition board is basically done. I reduced the amount of selectable resolution bandwidths to 3 (1MHz, 100kHz, 1kHz) and replaced the SA602 with an ADE-11X Mixer to reduce noise.As you can see in the diagram, PIN-Diodes switch between the RBW-Filters and are also used to steer the signal to the SMA-Connector that can send the 3rd IF to another board, as well as to provide the possibility to inject a signal directly into the final IF-Amplifier.As the 3rd LO I want to use an Si5153, because it allows fine tuning of the 3rd IF, as well as a wide range of frequencies, which makes the requirements for the 2nd IF and LO less demanding - 2nd IF can be between 20MHz and 150MHz basically.The chip can also be used to provide the reference-frequency for the 2nd LO.I haven't checked how strong crosstalk between the outputs is though and even though only Output 0 and 2 are used, with Output 1 being terminated into 50Ohms and deactivated by software, I need to perform some tests with the Adafruit-module I have here to verify that the chip generates a stable waveform.If that's not the case, the reference-frequency for the 2nd LO has to be generated by other means.Reference-frequency for the Si5153 will be provided by the processor-board (The 25MHz VCXO in the lower right corner), where I have space for a PLL to lock the VCXO to an external reference if available.

author: AF6LJ
author_rank: Unknown
timestamp: November 23, 2016, 03:55:00 am
content: Quote from: SaabFAN on November 21, 2016, 06:13:13 pmVery Cool.You can always add more selectivity positions later on as (or if) you need them.I was wondering how your project was going.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 23, 2016, 07:47:07 am
content: It is currently the project with the lowest priority (I have about 5 of which two include RF-Stuff).Btw. I just realized that I haven't put any aliasing filter between the log detector and the ADC. That will be corrected later this day^^At the moment I am not entirely sure how to build the analog aquisition board: except for the input to the Mixer, the board has to handle "only" 4MHz, so I am thinking about using veroboard and the Si5153 Module from Adafruit I have here, as well as SMD to through hole adaptors for the other chips. Would save me about 40€ for the boards

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 24, 2016, 12:42:37 am
content: I have finished an early layout of the aquisition board. Just placed the components in logical groups and took care to have straight lines for the RF-path. Nothing done to make it look more beautifulI also realized if I want to build it within the Eurocard-Formfactor, I have to order the PCBs. With the adaptorboard, the veroboard would be too small. Putting the power supply and the control for the Filter on a different board would probably give me enough space on the boards for everything.To shield the filters and the detector-stage, I thought about using copper foil and lego bricks as spacers to keep the foil from shorting out anything.Using small pieces of copper soldered to the board and then putting a copper foil lid on it should work too.To keep digital noise out of the analog system, I have separated the grounds for the analog and digital parts as much as possible. Unfortunately, one of the DACs needs to sit right in the middle of the analog area, so 2 rather long traces carrying the i2c-bus signals will run along the edge of the board to that particular chip. Fortunately, the i2c-bus is only used to configure devices that can be left alone for long periods of time (1kHz step scanning @ 1kHz RBW excluded - the Si5153 is being tuned about 1Mhz up and down in this mode while the 1st LO is tuned in 1MHz steps all other modes require only the 1st LO to be swept).The only Bus that is constantly accessed is the SPI-Bus. To get the data out of the ADC fast enough, I need to push the clock frequency as high as possible. I hope signal integrity doesn't become an issue here. Ordering these boards isn't exactly cheap anymore: 40$ + Shipping for 5 pieces.Any suggestions or advice about what to do and what not to do when doing the layout for ca. 30MHz fast digital signals? Do I need termination at the receiving end of the signals? Can I transport this signal via ribbon cable?

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 26, 2016, 09:25:29 pm
content: Revision A of the Aquisition Board.The vias along the coplanar Waveguide-trace for the RF-Signal haven't been added, but everything else is done.To avoid angles in the traces that carry RF I have used the Arc-Tool and made nice round corners.As you can see, I have basically kept the layout and just made minor adjustments to the position of the components.The Ground-Planes are connected at one location: Next to C56, which is in the Power Supply-Section of the board.By my estimates, the +5V Rail will require about 650mA worst case. This results in about 2,6W power dissipation in the +5V Regulator. With a safety margin, this amounts to 3W power dissipation in the regulator. The same goes for the the -5V Regulator. So these two will be equipped with heatsinks. The other regulators should be fine without heatsinks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 26, 2016, 11:35:50 pm
content: Is that one crystal filter really going to do 100kHz width? That seems unbelievably wide for crystals...Tim

author: SaabFAN
author_rank: Frequent Contributor
timestamp: November 26, 2016, 11:51:00 pm
content: Now that I think about it, you might be right about that^^The calculators on Changpuak suggest a shunt capacitor of about 5pF, which is probably too low to implement on FR-4.I'll build a Filter on the breadboard tonight and will look how well it performs.If it doesn't work or the loss is too high, I'll switch to a LC-Filter for the 100kHz RBW.EDIT: Just measured the Crystals and punched in the values I got to get the LCR-Values of the crystals. Now the calculator shows 4pF. No way I can replicate that on the breadboard or veroboard.So, it's going to be repurposed as a 10kHz filter

author: SaabFAN
author_rank: Frequent Contributor
timestamp: December 13, 2016, 11:14:25 am
content: I've run into a little problem: The analog frontend won't fit on a euro card (15x10cm). There is no way to fit everything on the board.So at the moment I'm thinking of reworking the design - Removing some parts, putting other stuff on daughter-boards, or simply switch to a large board where I can fit everything.At the moment I'm favoring the last option, which would mean that the boards would be oriented horizontally inside the case. With shielding on the top and bottom, I think I can fit 2 cards into a Schroff-Case, which will contain all the necessary electronics. On top of that case the processing-board as well as the display and the keyboard could be mounted inside a custom superstructure.Another option would be to put everything on an ever bigger board and put it all inside a custom-made case. I'll have to run the numbers on the different options, to see which one is cheaper.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: February 24, 2017, 03:49:19 am
content: I'm sorry there hasn't been any updates on this project.Back in November I managed to buy a Spectrum Analyzer for 650€ that includes basically all the functionality I wanted and more (its a 3Ghz unit and has all the features required for EMC-Measurement: R3131A by Advantest - Needs some adjustment and maybe new DACs in the IF-Amp, but other than that it seems to be working ok) so I've now shifted my focus towards the last item that was missing in my test-setup, an RF signal Generator, and also to the project that I want to be testing with all this fancy gear: DC-DC Converters for pleasure craftThis doesn't mean I'm abandoning this project entirely, but currently I don't have the time available to do this project too and get stuff for University done - After all, electronics is more of a hobby to me, while my studies and work is focused on 3D-Art for computer games.I am considering to combine both for my bachelor thesis thoughIf anyone feels like picking it up where I left, the schematics, as well as the layout for the aquisition board are available in circuit maker.Basically the two major obstacles I can make out so far are the layout of the analog frontend that needs to be divided across at least 2 euro-cards and the software. The aquisition board takes care of bringing the analog signal into the digital domain, so at least that part of the signal-chain is fully done (unless there are flaws in he layout, which I suspect isn't unlikely^^).

author: AF6LJ
author_rank: Unknown
timestamp: February 24, 2017, 04:54:29 am
content: This is a complex project and can be tough.I have thought about building an an analog spectrum analyzer however that is a bit over my head and finding the time is even more of a challenge.You have done well to get this far.