PLL VCO 1.6GHz or thereabout (for 9cm band transverter) - Page 1
Forum section: electronics / projects

author: Yansi
author_rank: Super Contributor
timestamp: June 12, 2016, 05:38:20 pm
content: Hi again! :-)Today, we have some crazy ideas for summer: My friend HAM is quite into microwave stuff, especially the 9cm (3400MHz) band (and above). He has made quite a few different builds of transverters for the 9cm band. Usually, there is a ovenized crystal oscillator (~100MHz or thereabout) and a cascade of multipliers up to abour half the band frequency (~1700MHz). Then a subharmonic mixer (sometimes called "russian" with two antiparallel diodes) is used to obtain the target frequency of 3400MHz.Background: The unobtanium crystal and the amount of work which has to go into construction of the frequency multipliers (unobtainium GHz-range trim-caps) being the second ... have lead me to an idea of the PLL and VCO.I'd like to ask, if it would be sensible or at least possible to replace that crystal osc (with unobtanium crystal frequency) and the cascade of multipliers with a PLL+VCO?I have a bunch of TSA5055 PLL chips laying around and also some nice 2SC5773 transistors I'd like to use for a prototype of such PLLVCO. The main concerns being the frequency stability and accuracy (stable and precise reference source of 3,2MHz for the PLL should be used) but also output jitter/phase noise. What do you think, would it be possible to build the 9cm band transverter (mainly to be used with an SSB transmission) around the PLL and VCO? Or is it completely stupid idea?I know, there are many integrated circuits nowdays, that could be sufficient for this, but as I have said, I have some parts that could be possibly used and as long as this is not a commercial project, possible failure to build it successfully won't harm anyone, but will be a valuable experience for me and maybe others.I don't usually design RF stuff, not this GHz magic at all, but am curious enough and have access to some proper measuring equipment, including spectrum analyser up to tens GHz.So should I try to build a PLL VCO for the transverter based on that TSA5055 chip or is it completely non-working idea? I'd like to at least try and then measure the performance.What I'd like to build is a "magic box" that would provide a stable frequency with low enough jitter/phase noise, at the range of about 1700MHz. The main parts of this project might be:+ Building a functioning and stable VCO for the target frequency (about 1700MHz)+ Making a signal buffer / splitter for the PLL+ Closing the loop with a PLLWhat literature would you recommend me to study first, if this idea is possible at all? What topology should have the VCO? (about 1700MHz, low MHz/V gain)Thank you for consulting my crazy ideas,Yan

author: edpalmer42
author_rank: Super Contributor
timestamp: June 12, 2016, 06:58:03 pm
content: I'm nowhere near an expert in this, but have you looked at brick oscillators? If you search ebay with this search string:(brick,"phase lock") oscillator, you'll find lots of surplus oscillators in the GHz range. Some have an internal crystal, some use an external reference which could be 5 or 10 MHz or in the 90 - 120 MHz range. Some have modulation inputs. Most can be tuned over a limited range. Often they are cavity oscillators that are phase-locked to a lower frequency reference. If the internal reference isn't to your liking, you can often remove the crystal and inject an external reference at a similar frequency and retune the cavity to get the output you want. Output levels are typically in the +10 to +20 dBm range.Ed

author: Yansi
author_rank: Super Contributor
timestamp: June 12, 2016, 07:07:47 pm
content: Thats not the answer expected. I can also buy for example Si4113 for a few bucks and have it done in an instant. The question was, if it is possible to be done more or less the classical way of PLL + VCO. One doesn't learn much from only using a pre-built block. I could also use a complete solution like some ApolLO-32 board, which I came accross a few minutes ago. But hell no, I want to build something myself.

author: awallin
author_rank: Frequent Contributor
timestamp: June 13, 2016, 04:43:20 am
content: Quote from: Yansi on June 12, 2016, 05:38:20 pmif you want to make it easy for yourself look at e.g. ADF4351 or LMX2541 or similar chips - might be hard to hand-solder but there are eval-boards available.http://www.analog.com/en/products/rf-microwave/pll-synth/adf4351.html#product-overviewhttp://www.ti.com/product/LMX2541the eval-boards usually have USB-control or if you make your own board you need something that talks SPI to the PLL+VCO to set all the parameters.

author: CJay
author_rank: Super Contributor
timestamp: June 13, 2016, 09:29:15 am
content: Quote from: Yansi on June 12, 2016, 07:07:47 pmYes, it can be done and much more easily than you might expect because there are PLL chips out there with integrated VCO which work in that range and much higher if you want to take the simple route.You'd need to cast a very critical eye over the specifications to see if they meet your requirements of course.If you want to make it more difficult then you can use an external VCO, I am experimenting with a few cell phone VCO modules in that range already and considering tripling the output but coming to the conclusion that for my purposes I may better off with a YIG.(I may not be successful but it's a hobby project and I'm learning)

author: Yansi
author_rank: Super Contributor
timestamp: June 13, 2016, 11:09:33 am
content: Yeah sure, I'd have that also as a hobby project. But really don't want to use a complete brick or PLLVCO integrated circuit, thats easy. Simple layout (needs only few caps around, maybe an inductor), one simple 50ohm output trace on a PCB, maybe a MMIC amp, done. But that's not fun.I'd like to learn how to do a VCO, how to amplify it's GHz output, how to split it, use the PLL, and so on. But really don't know, where to start. Is there any microwave literature for n00bs? That would cover designing oscillators, amplifiers, some filters, basics microstrip.. That'd be very handy.Yan

author: G0HZU
author_rank: Super Contributor
timestamp: June 13, 2016, 07:19:16 pm
content: Why not make the VCO at 3400MHz and dispense with the need for the harmonic mixer?There are plenty of PLL chips that will run at this frequency input and plenty of choice for active devices to use in the (printed resonator?) VCO at 3.4GHz.

author: Yansi
author_rank: Super Contributor
timestamp: June 13, 2016, 07:53:05 pm
content: Because I only want to replace the complex oscillator-multiplier section and reuse already built and working spare units with the subharmonic mixers. And the big advantage is you need only half the target frequency. So why not VCO at 3.4GHz? Why yes? That would be twice as hard. And I think making the 1,6GHz one is a challenge itself, for me.

author: hendorog
author_rank: Super Contributor
timestamp: June 13, 2016, 08:17:46 pm
content: Have you come across this site in your travels? There is some interesting stuff on building DIY VCO's.http://lea.hamradio.si/~s53mv/spectana/vco.html

author: deephaven
author_rank: Frequent Contributor
timestamp: June 13, 2016, 09:43:55 pm
content: Quote from: hendorog on June 13, 2016, 08:17:46 pmJust wow, amazing stuff on that site!

author: Yansi
author_rank: Super Contributor
timestamp: June 13, 2016, 09:50:14 pm
content: Well, right. Amazing stuffI have just finished reading about the spectrum analyzer project.Thanks for the tip on the VCO, the narrowband microstrip one seems interesting. (But I hate microstrips, due to being very large at ~1600MHz, so I'd better like to make the VCO from lumped components)

author: hendorog
author_rank: Super Contributor
timestamp: June 13, 2016, 11:15:56 pm
content: Quote from: deephaven on June 13, 2016, 09:43:55 pmYep he is a clever chap for sureI certainly found it inspiring as to what can be achieved DIY style.

author: G0HZU
author_rank: Super Contributor
timestamp: June 13, 2016, 11:55:15 pm
content: Quote from: Yansi on June 13, 2016, 07:53:05 pmOK, but FWIW the essential core of a (quick and dirty) printed resonator VCO at 3.4GHz would only consist of a cheap Minicircuits MMIC amplifier and two SMD capacitors along with the printed resonator which would be a small rectangle of microstrip. You would also need a SMD bias choke and some SMD bias resistors but the whole thing would only be about 2.5cm x 2cm in size. To make it into a VCO you would need to add a varactor diode and some supporting RLC parts, obviously.If you look at the phase noise plots in figure 9 on that linkhttp://lea.hamradio.si/~s53mv/spectana/vco.htmlThe (narrowband) printed resonator VCO would have about the same phase noise as the dashed line plot for his HP8593E spectrum analyser. Take some time optimising the design and it could be better than the analyser.

author: hendorog
author_rank: Super Contributor
timestamp: June 14, 2016, 12:03:10 am
content: Quote from: G0HZU on June 13, 2016, 11:55:15 pmSpeaking of which, if you have time I'd love to see some pictures of the 4.4GHz oscillator you made?

author: G0HZU
author_rank: Super Contributor
timestamp: June 14, 2016, 12:32:08 am
content: If you are interested I posted up some info about it (and a picture and simulation) here on post #46https://www.eevblog.com/forum/testgear/fft-spectrum-analysis-reviewed/25/The basic design aimed for a loaded Q of about 30 and osc power 10dBm at 4.4GHz. The resonator is a bit lossy so if the loss + device noise figure is 8dB then the phase noise at 100kHz can be approximated with a basic version of Leeson's equation as in the excel sheet below (this excel template is taken from P.Vizmuller's book)It predicts -121dBc/Hz at 100kHz and I managed about -119dBc/Hz with that quick and dirty design.There's a phase noise plot on post #36 on the link above to show this.The main trick with this approach is to make sure the phase shift round the loop is unity at the same place where the loaded Q is maximum. This is achieved in the simulation below if you look at the graph for QL = loaded Q. This is where there is the most group delay in the resonator so you get best phase noise and stability if the phase and group delay peak happen at the same frequencyIf it doesn't align then the phase noise and stability will be much worse than the prediction in the excel spreadsheet. So although the layout inside the yellow circled section below looks 'simple' the lengths of those tracks are optimised to get the correct phase around the loop. If I change the track lengths to the capacitors slightly then the phase noise will degrade.Note that the 'core' of the oscillator is contained in the yellow circle in the image below. So there is just the MMIC, the two caps and the printed resonator. Everything outside is just for the external biasing (and supply filtering) for the GALI 49 MMIC. To make this into a VCO I'd have to lightly couple a varactor diode to the resonator and this would degrade the phase noise a bit. But not by much if I kept it narrowband.

author: hendorog
author_rank: Super Contributor
timestamp: June 14, 2016, 12:36:58 am
content: Ah so you did - sorry I had seen it but forgot.Thanks for all that extra info, much appreciated. I will have a play around.

author: Yansi
author_rank: Super Contributor
timestamp: June 14, 2016, 09:05:10 pm
content: MMmmm. It's easy and nice if you know how to do it. But I'm really dumb, if it comes to the basic RF stuff. 99,9% of the time, I do "DC circuits" only with respect to these frequencies, so this is a sort of "challenge" for me to learn something completely new and different.One good thing though: I might borrow a spectrum analyzer from a friend who doesn't use it at all. It's some older model of a 3GHz Advantest gear I think. That will be hell of a helpful thing! At least for debugging of my VCO and other circuits.Maybe I should try more different VCO topologies and select the best one. So I'll try also the microstrip resonator / bandpass filter one. If I ever figure out how to design them to an arbitrary frequency and how to tune them.But first I should learn some basic stuff, which seems kind of a problem. I have borrowed few kilos of paper literature, but none of them is suitable for a curious beginner. It's either just pure impractical math-filled something about the space and god or whatever, or purely a construction cookbook for HAMs where you are supposed to copy that or that with 1:1 precision. (no explanations why this or that). If someone knows any suitable literature to begin with, please share! More than 1 may be interested to read.Thanks, Yan

author: G0HZU
author_rank: Super Contributor
timestamp: June 14, 2016, 09:11:11 pm
content: "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: Yansi
author_rank: Super Contributor
timestamp: June 14, 2016, 09:21:11 pm
content: Well. That was very hard to find. ()Thank you for the tip, will look inside and will report, if I can read it or not.

author: G0HZU
author_rank: Super Contributor
timestamp: June 14, 2016, 09:30:49 pm
content: Yes, the book is easy to find... It is written by the person who designed/introduced the Eagleware suite of RF CAD tools from the late 1980s onwards so the simulator you see in the book is his own. I've been using his Eagleware/Genesys suite since about 1990 for RF design.This SW isn't free but you could try using RFSIM99 which is an old but free RF simulator instead? It supports two port s parameter models so you can replace the GALI 49 amp in the simulation with MiniCircuit's model of this device. You can download the model from the MiniCircuits website. This is what I did in my simulation at 4.4GHz. Without this model you won't know how much phase shift there will be in the MMIC amplifier at 1700MHz. It won't be 180degrees up at these frequencies!

author: G0HZU
author_rank: Super Contributor
timestamp: June 14, 2016, 09:36:24 pm
content: Note that if you do go down the MMIC + resonator path then you won't get the 'best' RF performance in terms of phase noise or power consumption/efficiency. But you should be able to design something with low phase noise and 'predictable' phase noise performance because you can simulate the circuit 'open loop' as resonator + MMIC in series and then look at the gain and phase (and loaded Q) of the complete circuit.Do this and you have enough info to enter into a basic version of Leeson's equation to predict the phase noise.Look closely at the simulation plots I posted up earlier.These are just small signal open loop plots of a (matched to 50R) resonator and a 50R MMIC amplifier in series. It only becomes an oscillator when you join the two 50R ports together with the real hardware. As long as you have sufficient 'over unity' gain margin in the circuit and you get the phase correct you can predict where it will oscillate

author: Yansi
author_rank: Super Contributor
timestamp: June 14, 2016, 10:11:25 pm
content: I have downloaded and tried installing the RFSIM99, unfortunately unsuccessfully. Throwing an exception "cannot start .\SETUP.EXE" or like that.//EDIT: Now trying to download/install AppCAD which is what my friend uses for his stuff if I remember right.//EDIT2: Well, AppCAD seems to be fun. Successfully disabled the VERY ANNOYING SOUND EFFECTS there.//EDIT3: Mmmm. That's not an RF sim. Thats only some calculator-helper-tool for basic circuits.

author: G0HZU
author_rank: Super Contributor
timestamp: June 14, 2016, 11:58:15 pm
content: If you want to have a serious attempt at this and you only want to use 'free' tools then try downloading and registering the free version of Sonnet EM called Sonnet Lite. Register it to get 32Mb of memory.With Sonnet Lite you could draw a resonator and include the coupling points, then simulate it and export the results as an s2p file to import into RFSIM99. You could probably do the whole thing in Sonnet Lite because you can import s2p data models as well as export them but the Sonnet user interface is not that great for stuff like this. However, as an EM simulation tool Sonnet EM is the best IMO.All of the above will require quite a bit of determination/enthusiasm/time on your part in order to complete the whole process because you will be on a steep learning curve. Just to be able to do a simple EM simulation on Sonnet takes some learning time. But you would be able to get similar simulation results as I would using Genesys and Sonnet combined.See below for the official Sonnet Lite intro/demo. The user interface is very dated and clunky and it has been improved since this video was released.But it shows a few basic moves and takes you through the 'wizard' method of setting up a new geometry/project. With Genesys it's possible to avoid all this and do all the prep and PCB layout in Genesys and then let Genesys and Sonnet link up and do the whole process automatically. Much better and much quicker but Genesys isn't free SW.

author: hendorog
author_rank: Super Contributor
timestamp: June 15, 2016, 06:39:12 am
content: Quote from: Yansi on June 14, 2016, 10:11:25 pmHere is a link explaining how you can run it under Win 7 64bit using "XP Mode" (Haven't tried this myself):http://www.electroschematics.com/835/rfsim99-download/Sonnet Lite is really good for RF learning - don't let the older interface fool you, it works well and just takes a bit of learning.That is a rarity amongst free RF tools IMHO, they are on the same level as Ham Radio websites

author: Yansi
author_rank: Super Contributor
timestamp: June 15, 2016, 08:23:57 pm
content: Unfortunately, I have Win 7 Home Premium or whatever that is.After a little toying around with simulators, trying to at least get one going... I understand that it is quite overkill for me. At least now.So with a little help and inspiration from the books I have borrowed, let's try some fun first. (My HAM friend will help me try that thing)I have copied a design of a subharmonic mixer for 6cm band, only calculated new lengths of the stubs, according to the 3400MHz frequency and PCB used (0.8mm FR4, Er 4.6, effective Er 3.4 or so ---> 1.5mm width for 50ohm). The schematic and PCB is below. The design will fit into a tin-plated shield box.The original plan from the book also had that IF pre amplifier. However, I have made few changes to it. Can you please review my changes, if they are correct? I'd like to have some primitive 3,4GHz receive box for toying around. LO is not an issue now, I can borrow a functional one with OCXO and block of frequency multipliers.Changes to the amplifier: I have scanned the original from the book, so you can see my changes. Are they correct, or did I stupid?Note: Transmit path omitted for simplicity, I don't need that, now. Note2: Power will be fed through the coax line.The most important change is I have put the trimcap to ground instead of output - as I didn't quite like the output LC tank resonance would depend on the loading? Or am I missing something?The second change is that I have bypassed the 47ohm source bias resistor. Parasitic capacitance of the source RFC together with the resistor will dampen the Q of the input bandpass. (I don't expect any high Q or narrow bandwidth though) But just a little thought that may be potential improvement.Could you please check my changes and scream how I screwed?Thank you for feedback,Yan