School spectrum analyzer project. - Page 1
Forum section: electronics / projects

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: March 22, 2024, 06:21:55 pm
content: Hi, I am wondering if anyone knows any good sources for making spectrum analyzers. I looked at my local library and all I could find were some basic electronics 101 books.I don't necessarily need sources that explain how a spectrum analyzer works, but rather maybe you can point me towards sources that explain the design of the things used in such devices such as voltage controlled oscillators, IF filters, mixers, and so on.This is for a school project. In freshman year in my HS, we do something called a personal project that lasts about 8 months until sophomore year. We research, think about, and do our project. This could be baking, making a guillotine (yes someone made that in a previous year), or making a robot to help victims of forest fires get to safety. I chose to build an analog swept front end spectrum analyzer. I plan to make this work in a Tektronix 7613 mainframe. There will also probably be a lot of copying and mashing of different circuits.Anyway, I'm just a bit under educated on how certain things work. I am quite familiar with electronics, It's just that I can't find any good sources that explain in great understandable detail on how certain things work. All I know about a VCO is that a varidiode will change it's capacitance based on the voltage applied to it, and we can use that to make a VCO. I'm also a bit confused on how the hell a logarithmic amplifier works.My goal is to make a spectrum analyzer work with a bandwidth of 0-10MHz.My basic understanding of a swept front end spectrum analyzer is that it is just a superhederodyne AM receiver with wider bandwidth and can tune across a number of frequencies really fast.

author: CaptDon
author_rank: Super Contributor
timestamp: March 22, 2024, 06:52:26 pm
content: There is a VCO in the CMOS 40XX series that is good for a swept VCO. Very linear. Sadly, I forget the number. You'll need a good balanced mixer. making the front end track the local oscillator + or - your I.F. frequency is a bit of a trick. Going 0 to 10MHz may be far more challenging than going from perhaps 5MHz to 10MHz where you are only going one octave and not several decades. Coming off your balanced mixer you may want a crystal filter to keep some of the junk out of your I.F. strip. Log amplifiers have been around since the radars of the WWII. They usually involve the log function of a small signal diode. We used the non-linear characteristics in the S.T.C. Sensitivity Time Control because the strength of the echo diminishes as the square of the distance so the gain starts out low for close in echos and advances to max gain over time through a non-linear function. Remember in your analyzer that High-Q narrow bandwidth circuits take time to 'ring up' like trying to accelerate a heavy weight on a pendulum and then have the nasty habit of continuing to ring which is the quality factor of the Q, sharp peak, low loss. Point being 'if you sweep to fast across a band of frequencies the I.F. won't have time to properly respond. That is why the old tube type analyzers swept slow and used the same sort of long persistence phosphors like the radar scopes to get a usable readable trace at 1 to 5 sweeps per second. Of course, now it is all digital storage and LCD screens.

author: MasterT
author_rank: Frequent Contributor
timestamp: March 22, 2024, 09:34:28 pm
content: Very time consuming and very complicated. Better alternative is arduino + some RF IC, like si4732-a10 or similar.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: March 22, 2024, 10:29:32 pm
content: Quote from: CaptDon on March 22, 2024, 06:52:26 pmThanks, I'll look into that.Quote from: CaptDon on March 22, 2024, 06:52:26 pmYes, I'm planning to use 3 stages of standard 455kHz IF transformers and a crystal filter to improve selectivity.Quote from: CaptDon on March 22, 2024, 06:52:26 pmSlow sweep speeds won't be an issue for me. I can use a storage CRT scope such as the Tek 7613 or Tek 314.Quote from: MasterT on March 22, 2024, 09:34:28 pmI don't want to do something as simple as that. I already know like 4 people who are doing an arduino project where they use specialized pre-built devices, almost like a kit. I like to keep things as discrete and jellybean as possible.Plus I have 8 months to do this, so plenty of time.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 23, 2024, 12:08:33 am
content: No one expects you to build this, but you can Learn from the Master:https://lea.hamradio.si/~s53mv/spectana/sa.htmlThis was popular:https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1985/11/page23/index.htmlThe must have books for a beginner in RF:Experimental Methods in RF Design,Bob Larkin, Rick Campbell, and Wes HaywardHas a full Spectrum Analyzer design that is very good and inexpensive. Covers home made crystal filters well, at levels from beginner to advanced. Covers VCO design and Preamp / IF /RF amplifiers from DC to 2 Ghz Its a great book, but it has doubled in price recently, for an 8 month school project it's perfect.. Try to find it used or on inter-library loan. Goes into the theory and design of every receiver circuit element without high order math from a amateurs' radio point of view. Learn what is in that book and have a good start on a career. I think of it as a book that you'd have to pry from my cold, dead, hands...But NOT dumbed down like theARRL Handbook,of which OLDER like 1980s-1990s editions are a good read...NavyNEETS,the full set... Free from the US Navy...Art of Electronics,Volume one, Winfield Hill.. Probably can find a PDF on-line.You need this chart eventually:https://www.minicircuits.com/app/DG03-111.pdfYou need this chart now...https://www.minicircuits.com/app/AN40-012.pdf_-------------------------------------------------------You will eventually need the circuit in figure 6 of this:https://interferencetechnology.com/wp-content/uploads/2015/02/WyattArticle.pdfAlso make it with a 1 Mhz TTL Crystal oscillator-----------------------------------------------------Print out copies and download the images on this page:https://techlib.com/electronics/detect.htmYou'll need a rudimentary RF voltmeter, the above page is it. Dr. Wenzel made that page for me way back when I was building a SA, like two decades ago. Its accurate.You'll need attenuators:https://www.qsl.net/z33t/rf_step_attenuator_eng.htmlEventually you will want a Ebay "DDS" frequency synthesizer for testing and measuring resolution and level.For RF under 200 Mhz or so, Manhatten Style PC construction is great for beginners:https://qrpme.com/docs/K7QO%20Manhattan.pdfSnag some Analog Devices inc RF log Amps and Detectors... Their web site is a treasure trove for a beginnerLike these:,https://www.ebay.com/itm/166352071945?itmmeta=01HSMAM3EZGBGHTD6ZKK80N4PH&hash=item26bb5b2d09:g:rKgAAOSwKsFlFLEN&itmprp=enc%3AAQAJAAAA0EISSxez%2BBTXxKGsQFea8desWappsYYsz%2FnSnqNuzInJ8rr5A7OGWcg3xPL%2FHpJR4dAm3Ezj8EkPOLlidRfntmKKk7I%2FWGWCvFcJ2igsyf%2B6TpSgfCKaS10YeTcw3xzvehi4yjheZn3BaIzCvwXZfz1hoCE7%2BY0F9ssrStos%2Br5CdiobDBIDMEkeyRosjBwnX%2F85%2F5kv1USYFyMoSdK%2BaaL7hUWOVaYX0PMfy6i7v4hcfuro2xEOhwjxUXHP4Ai3pDlPypm9u8Bz%2B13hzrqujMU%3D%7Ctkp%3ABk9SR9S30IrNYwThere are other varients.Shop Class: Interdigital filters are a key part in High End Spectrum Analyzers with High Side IFs for greater performance. This is a Java calculator that helps you make them:https://www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.phpCan be made with hand saw, file, taps, and drill, but have your parents permission before using power tools and have supervision.This program, you may need later:http://www.hp.woodshot.com/One of my favorite tricks with Appcad is to turn hobby shop brass tubing into Solid Coax Cables and RF fittings such as cased diode detectors.https://www.broadcom.com/info/wireless/appcadAlso hosted at Broadcom...Lastly:www.minicircuits.comwww.rfparts.comwww.amplifiedparts.com(Great Knobs)https://www.rf-microwave.com/en/home/(Italy, but ships to US)www.mcmaster.com= Hardware treasure trove.Steve

author: mawyatt
author_rank: Super Contributor
timestamp: March 23, 2024, 12:54:56 am
content: Sounds like we have an up and coming future stellar Scientist/Engineer in the makingQuite a project for freshman college student, much less a HS student, so hats off for taking this onLots of good advice and info sources above.If you want to get somewhat lost in just a small section of the SA circuitry, look deeply into Log Amps, especially the more modern Successive Detection Types. We've utilized this concept often in IC design, even directly at very high frequencies.Good luck and please keep us posted on your project!!!Best,

author: LaserSteve
author_rank: Super Contributor
timestamp: March 23, 2024, 01:02:06 am
content: BUC, I'm done with updating my post. Good Luck.. Rf takes patience, and a lifetime of learning. Enjoy... I'll keep an eye on the thread.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: March 23, 2024, 06:47:17 am
content: Just a quick question that I probably already know the answer to; will these relays shown in the image be good for 10MHz? I would assume they would suffice, but I am discouraged by the complex attenuation system I see in low bandwidth scopes such as my Tek SC502 and Tek 5A18. The 5A18 is only 2 MHz and looks more sophisticated than what I was planning with these relays.The black relay is some kind of random relay I got out of a microwave oven, and the orange one is from the surplus of relays I used to build my CW transceiver. I'm not a total stranger to RF. And yes I have an amateur license. I bought these off amazon and they're advertised as signal relays. The transceiver works fine at 3.579546MHz and 7.1MHz with "faster?" (is that the correct word?) crystals. SOOOOO I would assume the relays work fine at 10MHz???My plan for this project is to follow this very rough road map. First, research and gain knowledge, start thinking about what I need for this project and if they would work well in it, design something, make a prototype, improve the prototype, make it look nice, design PCBs, get physical PCBs, 3D print a nice housing, assemble, showcase my project next year, done.

author: Bud
author_rank: Super Contributor
timestamp: March 23, 2024, 06:56:04 am
content: https://scottyspectrumanalyzer.us/

author: geggi1
author_rank: Frequent Contributor
timestamp: March 23, 2024, 10:09:32 am
content: i believe the "Experimental methods in RF Design" spectrum analyzer is the best option.By adding some modern components you will be able simplify the device.Add a DDS, Arduino and a Logamp (AD8307) you will be able to have a digital control and use a laptop as the display instead of a oscilloscope.

author: TimFox
author_rank: Super Contributor
timestamp: March 23, 2024, 03:33:10 pm
content: A couple of books, repeated from my post to a different thread about SAs:Two useful reference books about the previous generation of swept-spectrum SAs with digital control and analog processing (ca. 1990) with examples from Tektronix.(1) M EngelsonModern Spectrum Analyzer MeasurementsJMS, 1991; Practical uses.(2) M EngelsonModern Spectrum Analyzer Theory and ApplicationsArtech House, 1984; More mathematical background than (1).

author: RoGeorge
author_rank: Super Contributor
timestamp: March 23, 2024, 04:31:35 pm
content: Look in the Tektronix 'Circuit Concepts' series, too, i.e.:Spectrum Analyzer Circuits by Morris Engelson (1969)https://w140.com/tekwiki/images/5/53/062-1055-00.pdf

author: jonpaul
author_rank: Super Contributor
timestamp: March 23, 2024, 10:54:18 pm
content: see mini-circuts for amps. attn, mixers, VCO for RF/VHF,UHF bands,https://www.minicircuits.com/Use attenuators and protection, since mixers and front ends are prone blow out if overloaded.Jon

author: cncjerry
author_rank: Unknown
timestamp: March 24, 2024, 01:15:58 pm
content: I have a bunch of analyzers and recently bought an MMS but building Scotty's looked like fun, so maybe 5yrs ago, I bought a complete set of extra boards, all done by Osh, from a friend. He built it and really likes it. I doubt i will ever build it, but having the boards is a motivator.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 24, 2024, 02:27:16 pm
content: If you can change the range to about 50-800MHz, you can modify an old TV tuner.http://www.gbppr.net/wireless/appendixF.html#9Or mod a cheap RTL-SDR. There's software to use a RTL-SDR as a spectrum analyzer, but the latency of the frequency select makes sweeps very slow. If you could have a microcontroller take care of the sweeping and somehow sync the data capture to it, it can work much faster.

author: kimballa
author_rank: Contributor
timestamp: March 25, 2024, 04:28:12 pm
content: What an ambitious project! I think that's a pretty cool challenge to take on. Good luck!I would definitely advise you to buy a VCO IC. I built my own analog VCO and that alone took 6 months to get right. You can do it, but you have bigger integration projects to focus on.There's an SSM chip that will do that for you. I forget the number.Typically for a VCO you want one volt of input control voltage to double the frequency it outputs. This means an exponential conversion of f_out = 2^(Vin). That's where the expo /log converter comes in. This is the tricky part of a discrete VCO to build. It's a very sensitive circuit, needs temperature compensation, etc.VCO ICs should have one built in so you can just input a 1V/octave control signal and it takes it from there.There's a community of DIY music synthesizer folks online. VCOs and amplifiers is what it's all about. If you search for "DIY synth" or "sdiy" you will find a lot of resources including open source schematics for things you could repurpose for your homebrew test equipment.Check out the "music tech DIY" forum at modwiggler.com. Lots of helpful folks and links to more resources there.

author: MisterHeadache
author_rank: Regular Contributor
timestamp: March 26, 2024, 12:06:00 am
content: I actually built the Wes Hayward design about two years ago. I put together a three video series on it on my alter-ego YouTube channel, here's the playlist:https://www.youtube.com/playlist?list=PLYNQ4erd0Qw_i-QfPq328sHskbDIZSACkAlso Wes still maintains some additional notes and subsequent mods on his design on his website.https://w7zoi.net/sa-stuff.html

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: April 22, 2024, 06:09:45 am
content: Update: So I finally got around to actually starting some prototype designs, and I've got down two of the main parts. The mixer and VCO. I still need the detector, log amp, attenuator, LPF, and other stuff; those I'll save for another weekend.For the mixer, I've tried using a ring diode mixer mentioned in some of the sources provided. But I just couldn't get it to work. I think it's just the very low impedance of my transformers. They only start to be effective at 100MHz from my Tek 191; I think that's just the RF transmitting from one side of the board to the other, and not actually being conducted.So I opted for a different design. I remembered that my dual tube transceiver project that I copied from LA6NCA used a 6BE6 pentagrid converter tube to mix the LO and the RF in to make a CW tone, and I just so happened to have a couple extra 6BE6s lying around. So I just decided to use that; it worked perfectly. I could have just used a dual-gated MOSFET, but I think using tubes is just much cooler.Also, about the VCO, it has a range of about 5MHz to 8MHz, so that limits my bandwidth to 3MHz. I wanted 10MHz, but that's proving difficult. Most of the sources I see are using commercially manufactured VCOs; they're also for microwave ranges.Anyway, just a brief update. It's 11pm right now and I need sleep.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: April 22, 2024, 06:32:25 pm
content: Quote from: CaptDon on March 22, 2024, 06:52:26 pmIs the 74HC4046 what you were thinking of?

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 20, 2024, 01:59:45 am
content: Last week the project officially started. I need to do my research first and write a few journal entries on that.One thing I'm a bit confused on is why do some spectrum analyzer designs utilize two mixers instead of one? The first one mixes the RF input and variable LO, and the other mixes the filtered IF of the first mixer stage with a fixed frequency LO.I see this design with superheterodyne radio receivers as well. I tried looking it up and tried to find answers myself. But to no avail.If I were to guess, it would be used to further improve selectivity? But that can be improved with just a better filter right?For my project, should I use two mixers? Or just one? I think just one is enough right?I've also renamed the thread to "School spectrum analyzer project"

author: KE5FX
author_rank: Super Contributor
timestamp: May 20, 2024, 03:14:27 am
content: Quote from: BlownUpCapacitor on May 20, 2024, 01:59:45 amThe double-conversion block diagram is used for image rejection. Remember that you're building a radio at the end of the day, one that receives signals at both LO+IF and LO-IF. If your LO is too close to the frequencies being received, it will be hard to build an RF input filter that rejects the unwanted input image frequency for all possible LO frequencies.A common workaround is to use an LO that is higher than the highest RF frequency to be received, so that the image on the other side of the LO will be so far out of band that it is easy to reject with a simple inexpensive filter. The IF then ends up between the lower end of the LO tuning range and the upper end of the RF range. This might be several GHz, so another conversion is then used to bring the first IF down to a second IF frequency where it's easier to filter and amplify.Coming up with the right conversion scheme can be tricky in more complex designs. Spectrum analyzers with four conversions were common in the past, but nowadays it's becoming more common to convert the signal to DC baseband right at the second mixer or even the first, doing the job with expensive ADCs rather than even more expensive RF parts.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 22, 2024, 06:24:14 pm
content: I just had a new idea. My original LO frequency range was meant to be 12MHz-22MHz to get that 10MHz band, but as you can see, 12 and 10 are awfully close to eachother, and according to KE5FX, it's not particularly good to have the LO so close to the measuring bandwidth. From low pass filter I'm thinking of, with a low pass frequency of 10MHz, 12MHz will still pass through the filter. Yes it will be attenuated, but that may mess with my project.Other people pointed out why not just use a TV tuner module? Well that's because that will only tune TV bands. So what I was thing was, instead of using the tuner as a whole, why not use the tuneable local oscillator inside the TV tuner? Then I have a reliable LO and I'm not limited to what the TV tuner is designed for.Does this sound like a genius idea? Or is the idea flawed?

author: geggi1
author_rank: Frequent Contributor
timestamp: May 23, 2024, 04:05:49 am
content: I see that you have been using a DIY mixer.These does ususlay not have good slelectivity and can be a bit noisy.Try to get a fabricated mixer because then you will have propper data on its performance.You might be able to scavange a mixer from some old rf gear.

author: Sensorcat
author_rank: Regular Contributor
timestamp: May 23, 2024, 09:16:33 pm
content: Interesting project!Perhaps you could post what test equipment you have, because that way we know what you can do when it comes to analysis and debugging of your modules (and what is out of reach).

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 23, 2024, 10:03:37 pm
content: Quote from: Sensorcat on May 23, 2024, 09:16:33 pmTektronix 2230Tektronix 7904Tektronix 7613w/7B85, 7B80, 7A19, 7A26, 7B53A, TD-1085/UTektronix SC502Tektronix DM501A x2Tektronix DC504Tektronix PG501Tektronix TM503 and TM504Tektronix 314Tekpower 50v 5 amp dual supplyBK Precision 4040Tektronix 5110 w/5A18N, 5CT1N, 5B10NTilswall Soldering Unit RJ969. This is an excellent soldering unit I've been using for a couple years. Still works great. I recommend this iron.Tektronix 191Longwei 30V 10A supplyHantek DSO2C10 hacked up to DSO2D15Global Specialties 4010HP 427A, This meter is in my profile pic.(I keep forgetting I have some stuff so I have to keep editing stuff in)A lot of stuff for a 15 year old eh? My local e-waste center sells this kind of stuff for very very very cheap. The 7904 was $50, the 5110 with all plug-ins as $75, and the BK 4040 was $20. Just some small repairs and cleaning were all that was needed.If need be, I can go there again and see if they have something I need.There are these two guys with TM500 units attached also for $100 each including the cart. Just wanted to share

author: Smokey
author_rank: Super Contributor
timestamp: May 23, 2024, 10:31:17 pm
content: Learn how to make a real circuit board and have them made at JLCPCB or something. However your project turns out, you will at least be able to make circuit boards at the end of it.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 23, 2024, 10:37:36 pm
content: Quote from: Smokey on May 23, 2024, 10:31:17 pmAlready do!https://youtu.be/02W6lhY8H5M?si=VaUy5YmIQaYIvUBlJokes aside, I will. I have already designed a few PCBs on easyeda and ordered from jlcpcb. I get free pcbs from jlcpcb essentially turns out. If you use easyeda you get a $8 coupon everymonth that covers the pcb cost. If I order say a $7 pcb, and use the $8 coupon, all I have to pay for is shipping.

author: Sensorcat
author_rank: Regular Contributor
timestamp: May 24, 2024, 09:47:15 pm
content: Quote from: BlownUpCapacitor on May 23, 2024, 10:03:37 pmOK, your situation is completely different to what I imagined. I don't think anything important is missing. That's good, because building an instrument without an instrument is almost impossible.So you are 15? It could be that you are the youngest person to ever build a spectrum analyzer. And once you succeed, the only problem is that many people will not be able estimate the achievement.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 25, 2024, 07:02:25 am
content: Update: Don't expect anything new until June 10th. I have finals coming up and my grades are falling behind. A series of screw-ups and simple mistakes cost me a bit.

author: zapta
author_rank: Super Contributor
timestamp: May 26, 2024, 02:43:23 am
content: Have you considered to use a fast ADC and FFT algorithm, e.g. on a raspberry Pi or a PC? It may be easier to design and more flexible to use. Just sample a short burst of samples at 20 Mhz, and use a python script to compute the FFT and display the graph. The python script is trivial once you read the burst of ADC samples.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 26, 2024, 03:34:56 am
content: Quote from: zapta on May 26, 2024, 02:43:23 amI could, and that would be easier, however, the school requires that I learn something very significant from this. I think if I do that, I'll learn how to code and use uCs, and some RF design, but not much else in terms of electronics I think.A swept front end would give me lots of experience in RF and electronics design. Plus I have until January to complete this. That's nearly 6 months. Really the project is due near end of December, as I have to write up a 25 page report on this project, but still almost, or maybe more than half a year's time for this project. So it can't be too simple.

author: zapta
author_rank: Super Contributor
timestamp: May 26, 2024, 05:03:55 am
content: Makes sense. I don't know what the requirements at your school are, just speculating.If you want to add complexity, once the fft analyzer works, you can add to it a frontend mixer that will shift a narrow band from high frequency to lower frequncy. This will give your analyzer high resolution and at high frequency bands. Probably much better than you can do with mixer only. And then you can record it over time and generate a spectrum over time graphs. It's a good segue to SDR and signal processing.https://training.dewesoft.com/images/uploads/29/fft_3d_measurement_1587721452.png

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 26, 2024, 06:48:13 am
content: Quote from: BlownUpCapacitor on May 25, 2024, 07:02:25 amYea, uhmm, I got bored from studying Chemistry after an hour and decided to create a 3D model of the Tektronix 5000 series plug-in chassis.https://www.tinkercad.com/things/iGbtzBgoZeZ-tektronix-5000-series-plug-in-shasseeI plan to 3D print this and use it to make my project work in a Tek 5110. I just need to figure out how to do that in the first place.Stoichiometry hurts my brain sometimes.Anyone know some good pointers for Lewis structures too?

author: erikka
author_rank: Regular Contributor
timestamp: May 26, 2024, 11:33:16 am
content: In case you have still time to consider options you could search ebay.com for these modules "rf oscillator voltage controlled"They come in different frequency ranges.Using such a module, a mixer, a band pass filter at the high if frequency, a second module and mixer for the down conversion to the low if where you have the resolution filters, your most difficult components become the high if filter and the resolution filter(s)For the log power detector you can use a AD8307 module, also from ebayThe log power detector doubles as a generic rf power meter that you can use, together with one of the vco modules, to test your if filter.You can use a 4 opamp ic and some potmeters and other passive components to build a voltage sweeper where you have one potmeter for the center frequency and one for the span.In this way you can build an sa without microcontroller, using a xy scope for display, and I know it will work as I did build it.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 31, 2024, 05:00:29 am
content: So I made the 3D model easier to 3D print:https://www.tinkercad.com/things/82Jht3C4EZv-3d-printableAlso, my finals start tomorrow... and my first one is chemistry. Wish me luck on figuring out Lewis structures, stoichiometry, atomic theory, and literally everything else as a freshman with 45 seconds per question.Thanks.Update: I think I got at least a D-

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: June 02, 2024, 08:24:09 am
content: If you want to view up to 500 MHz with a few Hz resolution bandwidth, this simple idea is hard to beat... not really what you are looking for but a fun and very low cost way to check IMD and keying bandwidth of transmitters.https://www.qsl.net/g4aon/ssa/SJ

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: June 15, 2024, 04:52:26 am
content: Does anyone have any tips on creating LC oscillators?So while experimenting with a super simple variable resolution filter, I finally decided to ask about this pet peeve.So whenever I make an LC tank circuit for, well, ANYTHING, there is always something wrong. Either the Q of the system is too low, or the inductance of the coil is calculated wrong somehow and the resonance of the tank circuit is off by a few megahertz. And when I move my hand too close, the thing changes its resonance also. Same thing with an oscilloscope probe when I'm trying to tune the thing with a trimmer cap, and when I remove the probe it oscillates at a few megahertz higher AFTER I installed it in such a way that I can not fix it.So far, the only thing that could possibly bypass the scope probe thing that I've thought of and tried myself is using a different coil to induce an AC magnetic field in the tank circuit and use another to pick up the resonance from another coil that feeds into a buffer to prevent any capacitive changes that would mess up my resonance. But my hand, even 4 inches away messes with it when trying to tune using this method.Does anyone here hold some tips they can share that would help?

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: June 15, 2024, 07:47:49 am
content: And you want to build a spectrum analyser? Making an RF oscillator is pretty basic stuff, your image shows both a crystal and an inductor, and a physically large inductor at that!Either you want an LC oscillator, or a crystal one, don’t try to combine them.There are literally hundreds of circuits on the web for crystal oscillators, one of the most reliable types is the Collpits oscillator. If you want a really clean crystal oscillator, there are techniques to do that too. This set of low noise beat frequency oscillators are based on work by Ulrich Rohde ( of Rohde and Schwarz fame):https://www.qsl.net/g4aon/pdfs/BFO%20v2_3.pdfSJ

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: June 15, 2024, 04:36:35 pm
content: The main reason why I'm using a tank circuit is because it offers a low impedance to other frequencies compared to a high impedance for it's resonance frequency. This is something a crystal can not provide as it is inverse. The crystal has a low impedance for a single frequency (ignoring spurious resonances) and a high impedance for other frequencies.I've also gotten around the LC resonance shift problem by shielding the crap out of it using copper clad boards or some other thing. This has worked okay, but it uses more material than I'd like, thus my question of tips. But if it is the only true way, I guess I'll keep doing that.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: June 23, 2024, 05:25:36 am
content: Progress report:After a while of trying to make my own ring modulator, I gave up as I didn't have any of the correct parts; it would also be more economical to buy a commercial one instead of buying the parts I needed.So instead of using a ring modulator, I decided to use a 6BE6 tube for mixing as I happened to have some extra after my tube transceiver project. It worked very very well at audio frequencies, but the higher the frequencies got, the worse the tube performed. This was likely me setting up the tube improperly, but I just really didn't want to deal with it anymore as it was getting hot and deforming the plastic on my breadboard.So I gave in and bought a ring modulator from Digikey. After the parts arrived, I swiftly assembled a very crude prototype/proof that I could solder a piece of metal to another piece of metal.The thing has no detector or log amplifier. It has no good way to adjust the center frequency nor the frequency span. But it works. All it has is a mixer, a crystal filter, and a very bad and not very reliable VCO. The VCO issue is just me using a very scratchy trimmer pot for R1 I pulled out of some random board. I am probably going to just buy some VCO off ebay instead to ration my sanity well.Here is a video of me stuttering a lot while struggling to speak normally:https://youtu.be/8rkVdlCWSvII have chosen to not use the 5110 anymore, and opt to use my 7613. It is variable persistence storage which makes it an excellent display unit for a spectrum analyzer. The downside is that it will take more effort to properly fabricate a plug-in module for it as it uses that special alignment plastic bit on the rear of the plug-ins, non-similar to the 5000 series or 500 series where they don't require such things.I also somehow managed to pass chemistry with an A, if anyone was curious.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: June 24, 2024, 08:32:05 pm
content: I've designed a promising sweep generator design using some simple components.It operates by using a 555 timer to generate a square wave, when then gets fed into the sweep generator. It consists of a simple capacitor charger, and when the 555 timer outputs a hi signal, the NPN transistor turns on, quickly discharging the capacitor, and when the 555 timer outputs a lo signal, the transistor turns off, allowing the capacitor to charge again. This capacitor charging and discharging is buffered through an OP amp, and will later be amplified by another op amp.I have chosen a fairly large value for the discharge and charge capacitor as I have discovered that the greater the value, the more linear the sawtooth waveform's rise is. But this comes at the downside of reduced signal amplitude, which can be rectified by using another opamp to amplify this signal.I chose this method for creating a sweep signal because the 555 timer outputs a square wave that can be used for blanking the z-axis. The squarewave's phase directly aligns with the time the saw tooth wave is not sweeping/ retracing, which fits my needs. This will remove the issue of the SA redrawing everything in reverse, which was an issue in my mockup design. The only possible issue I see with it is that the re-tracing happens exactly when the square wave goes hi. This can mean that the trace doesn't fully blank before the sweep re-traces. It would be nice if there was some way to add a delay to when the 555 timer goes hi, to when the discharge transistor turns on. Maybe I can use an arduino to add a 50ms delay to that. I will be incorporating an Arduino anyway to display center frequency and other stuff on an LCD display. I can't figure out how to interface the readout on the 7000 series. It would be nice if I could figure it out because if I did, I could just use that instead of a separate LCD display.So this will require only two ICs, as I will be using an LM358 dual op amp, which covers the two op amps: the buffer, and the amplifier. The other IC will be the 555 timer.Here is my circuit:https://tinyurl.com/2j9pu69m

author: Sensorcat
author_rank: Regular Contributor
timestamp: June 24, 2024, 08:50:37 pm
content: Quote from: BlownUpCapacitor on June 24, 2024, 08:32:05 pmHmm. The 555 is not a very stable source for clock and timing signals. Since you seem to aim at about 20Hz, you can use the Arduino for all timing signals, including the delay signal. It is accurate to generate slow signals with a µC, because the timers/counters reach large values. To get the Arduino stable, add a quartz oscillator, if your module does not already have one. The internal oscillator of the µC will likely drift as a 555 does.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: June 24, 2024, 08:56:57 pm
content: Quote from: Sensorcat on June 24, 2024, 08:50:37 pmI'll take the advice for using a uC for square wave generation. It would also give me more control over the duty cycle of the square wave, which is good as I can adjust the sweep hold-off that way. I don't think clock cycle drift is a huge problem as I know that the sweep frequency can vary by approximately +-10%. I was planning to add a variable control for sweep speed on the front panel anyway. I guess I can add a rotary encoder for my Arduino to use to change the sweep frequency.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: June 24, 2024, 10:04:14 pm
content: The circuit works well on the breadboard using an arduino to drive the discharge transistor. I noticed that the falling side of the waveform wasn't that clean, but I can just blank that away.You may notice that the trace seems quite bright, and that's because I have to put the intensity quite high to capture the waveform using a camera.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: July 10, 2024, 05:44:45 am
content: So I made a 3D model of the mating part for the 7000 series mainframe plug ins:https://www.tinkercad.com/things/bED8Zr7AeYU-frantic-tekworkI don't have a 3D printer to I'll have to wait until late August to hopefully print it; maybe the computer science teacher won't even let me print it because of its size. But I have (some) confidence in my tinkercad skillsSo I have everything I need to make a 7000 series plug-in chassis.Those of you who are more observant and more savvy with tek plug-ins may notice the lack of the PCB mater, and the weird 4 hole thingy on top of the part. That's because through my geniusness I have concluded that the effort to model the PCB mater does not meet my effort-to-product ratio requirements. This is because I am hoping that my future self will be able to design the chassis and the PCB to fit into the mainframe socket without the need for such a PCB mater to hold the PCB secure.Also, I don't know what the 4 holes thingy on top of mater for tek plug-ins are for. So I didn't model it.I'm also taking an interest in trying to understand the readout system of the 7000 series mainframes. My hope is to be able to use that to display the center frequency of the spectrum-analyzer and some scale factors. I am, however, struggling to do so and might just use some of my own vector graphics if I can figure that out.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: August 29, 2024, 04:09:00 am
content: Got busy with summer school and taking PE over the summer. I should have taken pre-calc over the summer as well... if I want to get into HL math I'd have to take AP calc over the summer. Did I screw myself over by not taking pre-calc over the summer?Enough blabbering, I have significantly improved my VCO design since I started working on it again in mid-August. I get a maximum reliable frequency modulation range of about 12MHz with some 1MHz headroom. More than enough for 10MHz.It's a simple Colpitts oscillator with two varactors for frequency modulation, and I used an air core transformer using two air core inductors, one smaller than the other so it can fit inside, so one inductor is the oscillator tank circuit part, and the other is the pick-up inductor. I chose this design because I noticed the circuit is very sensitive to directly connected external loads during testing. This magnetic coupling solved this issue.I also got my hands on a free Formlabs Form 2 3D printer. It's in pretty rough shape and doesn't print very well because of a severely bent z-axis I just bent back more or less straight. It can print simple shapes without too many issues. This means I don't have to wait for the school 3D printer queue.In the images, the bottom trace is the magnetic coupling output. The top trace is the input modulation signal; it is ground referenced to the center horizontal graticule and is Channel 2.Edit: Oupes, the photos are upside down. I can't seem to correct it. I think the EEVBlog forum image system is automatically rotating it 180 degrees for some reason.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: February 02, 2025, 03:57:47 am
content: Alrighty, I finished the project, and now I need feedback on the aesthetics of the product. As an engineer/hobbyist/or someone with experience in EE, what are your thoughts on thevisual appearanceof the product? I need this feedback for my report that I have to write up.I will release schematics later after I organize them in a way that you don't have to jump from project to project and painfully follow the theory of operation to figure out which jumper connects to which board and so on.This has a bandwidth of 70MHz to 80MHz. It works in my 7613, but turns out I didn't need the storage capability of that scope because it works fine at high enough sweep speeds that don't cause epileptic seizures.Also I apologize for the poor resolution images. I will maybe get better resolution images once I find my smart phone. These were taken on a 2011 handycam.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: February 02, 2025, 06:52:57 am
content: Better imagesfiles too big so I'll make two replies

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: February 02, 2025, 06:54:34 am
content: the 3rd

author: Sensorcat
author_rank: Regular Contributor
timestamp: February 03, 2025, 11:34:37 pm
content: Congratulations for finishing this ambitious project! I was glad to see your post, because I asked myself a few weeks ago what happened to you, since you all of a sudden stopped posting.Regarding your question:The PCBs and the frame look very good. More than any teacher can dream of in a school project.What I don't like so much when specifically aesthetics is wanted, is the front. Another copper-clad PCB, perhaps painted with clear coat for protection, and you would have a smooth surface. Also, some writing on the front would not hurt, since you put so much effort in the project: What is this module, who made it and when, what is the BNC input spec, how does the pot scale, the usual stuff.Finally, since this project will certainly not your last, I would like to draw your attention to the fact that good electronic systems are only possible with good mechanical design. I suspect that the PCBs that do not fill the frame from top to bottom could need better mechanical support. Not in the sense that I think it will fall apart in the lab. But since you called it a product, think about the peak acceleration possible during shipment (parcels get thrown around) or transport in a car (potholes).Since it is a school project, it's an A for me, A+ if you post nice sample measurements (hope I got the american system of grades right, with A the best).

author: Smokey
author_rank: Super Contributor
timestamp: February 04, 2025, 01:52:34 am
content: Good job sticking with it and finishing a project.Aesthetics might not be the right concept here.You can talk about good industrial design, or good user interface design, or robust mechanical design. Those are all important from a functional standpoint. Ultimately if you are making a spectrum analyzer the most important thing is does it function as a useable spectrum analyzer.Have some real PCBs made. Now you can say you etched your own boards once, and move on. This is a skill that essentially zero employers or customers values at this very moment in history. This is a cheap and easy way to make your designs look significantly more professional and more functional from the standpoint of reliability and also silkscreen options for annotating stuff.If you had real boards made, you could have used at least a 4 layer board and gotten better ground plane coverage and impedance characteristics, which if you are making a spectrum analyzer actually probably matters, even at 80MHz.It also looks like you could probably combine all those boards into one PCB. That would help, especially with the cabling.If you already had the designs in some PCB CAD software form, you were like 5 clicks and $25 away from having actual professional boards in less than a week, which is a skill that is presently actually marketable.Use real connectors and board to board cables. Point to point wiring, unless there is some specific technical reason to do that for some specific signal type or another is sort of a nightmare. If you must point to point wire stuff, use cable management techniques like they used to in the old days. Cables bundles, cable ties, anchor points to the case, etc. Also don't forget to run grounds along with any signal cables to reduce loop areas. Don't rely on one ground wire in the corner of the board to cover all the signals.I agree with sensorcat. Fix the front panel. A PCB (sourced from a real PCB house) is a good option. SendCutSend is another good option if you need it to be metal. They can laser cut all kinds of stuff.

author: Brociall
author_rank: Newbie
timestamp: April 25, 2025, 03:56:17 pm
content: Quote from: BlownUpCapacitor on March 22, 2024, 06:21:55 pmWow, your school project sounds quite interesting