Measuring output from 10GHz oscillator on 6GHz spectrum analyser? - Page 1
Forum section: electronics / projects

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 05, 2015, 08:56:15 pm
content: I am trying to solve a little problem. I have 10GHz Gunn diode oscillator that I built and I want to measure its output frequency with reasonable accuracy. I have spectrum analyser that spans from 9kHz to 6.2 GHz and 3GHz RF signal generator. How I can do it? I figured that I can purchase a additional mixer like this one here:http://www.ebay.com/itm/REMEC-MAGNUM-MICROWAVE-Double-Balanced-Mixer-RF-6-0-12-5-GHz-10dBm-MC64PG-11-/251660398164?pt=LH_DefaultDomain_0&hash=item3a9820ee54and then I can feed RF from the oscillator into RF input of mixer, 3GHz signal from RF signal gen into LO input and I should see ... fIF = fRF-n*fLO - only second harmonic of the mixed signal at 4GHz, right? It will be significantly weak since it is a second harmonic? Have anyone here done this kind of thing? Will mixer like one I linked work for me?I found that most of mixers have IF output significantly lower than 2GHz, which means that what I will see is not even 2nd harmonic.

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 05, 2015, 09:09:01 pm
content: According to the specs of this mixer:MC64PG-11RF: 6.0 - 12.5 GHzLO: 5.0 - 15.0 GHzIF: DC - 2500 MHzLO starts at 5GHz, IF is only good to 2.5GHz.It's hard to say if it will work good enough, maybe it is easier to try if anything shows up at the SA when you directly connect the 10GHz to the input. You could see something on the 2nd harmonic of the SA's LO.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 05, 2015, 09:37:53 pm
content: Quote from: PA0PBZ on March 05, 2015, 09:09:01 pmActually you are right, LO is outside of range for my rf gen. It won't workManual for spectrum analyser shows how to find harmonics that are multiple of fundamental frequency which are at -20db. Nothing about fractions

author: KJDS
author_rank: Super Contributor
timestamp: March 05, 2015, 09:40:58 pm
content: It's pointless directly connecting the 10GHz signal to the spec ana, they always have a decent low pass filter before the first mixer, partly to remove any noise that is at the first IF frequency from disrupting the SA but also to stop other signals causing unwanted affects.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 05, 2015, 09:49:09 pm
content: I use a Satellite LNB preamplifier with a 9.6 or 10.0 Ghz DRO based Local Oscillator as a Downconverter for my 1.5 Ghz Spectrum Analyzer. I need to look at 10.224 and 10.368 Ghz for my Ham Radio 10 Ghz rig.You can also get PLL based LNBs with similar LO frequencies if you like higher accuracy.Jumper out the LNB's microstrip OUTPUT low pass filter if you need to, using some solderable shim stock as a microstrip. Add 2 to 20 pF of coupling cap to isolate the DC bias. I use a 20 pF 1026 SMD cap.Leave the INPUT microstrip filter in place, its broadband enough for your use.Place a resistive pad between the LNB and the spectrum analyser input until you are sure the input level is safe.Unless you wish to build a Bias Tee, you'll also need to open the LNB and remove the power injection network. The LNB normally gets it's power from the output coax center conductor at >= +15 Volts. Leave the LNB''s bias board intact and powered. Many LNB need a negative bias for the low noise FET or pHEMT devices, which is generated by the bias board.Chose the local oscillator frequency in the LNB with care and you will be very happy!I've had good luck with this model (NJR2784H) and a low gain, home made, horn as the antenna. The match between the horn and the LNB waveguide can be quite poor or mis-sized, the LNB has more gain then you will need. With a Gunn Diode in the near field, you will not need a receive horn at first, the open waveguide is fine at close range.A simple diode harmonic generator driven by a 2 meter handheld or 96 Mhz clock oscillator will give you a reference frequency if you need it, for calibrating the DRO. You only a few microwatts of radiated power from the marker harmonic.http://www.ebay.com/itm/NJR2784H-Ku-Band-DRO-LNB-900kHz-Stability-New-/131002242567?pt=LH_DefaultDomain_0&hash=item1e80579607Find a copy of "The Gunnplexor Cookbook" as well.Your alternative is subharmonic injection (N/2, N/4, N/8 ) etc on a surplus 10 Ghz mixer. That's going to require extreme care with the drive levels. If your SA has a tracking generator, in "theory" you could use that for subharmonic injection drive.SteveLinks:http://www.ham-radio.com/sbms/sd/lnb2.pdfhttp://ea4eoz.blogspot.com/2012/09/lnb-and-its-ham-radio-usage.htmlhttp://www.qsl.net/pa3gco/zelfbouw/blauwkap/bluecap.htmlHorn I enjoy making and using:http://myweb.tiscali.co.uk/g4nns/FeedHorn.html

author: Marco
author_rank: Super Contributor
timestamp: March 05, 2015, 10:47:06 pm
content: Onchangpuak.chthere are complete design files for Target3001 (free for non commercial use) for an upto 12 GHz x1000 frequency divider.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 05, 2015, 10:55:32 pm
content: Thanks a lot for great info Steve!I checked the LNB that you are referring to - it appears that it is designed for frequencies from 10.95 to 11.7 GHz. I am not sure if internal dielectric resonator can be tuned down to 10GHz. So ... I need an LNB in order to extend range of my spectrum analyser so that I can tune my Gunn oscillator and for that I need to tune DRO inside LNB and to do that I need 10GHz reference which brings me back to where I startedI have 10 MHz rubidium standard which I used to adjust oven oscillator in RF signal gen that I have (one that goes up to 3GHz) so at least I know that I can get pretty accurate 100kHz-3GHz signal.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 05, 2015, 11:09:13 pm
content: Quote from: Marco on March 05, 2015, 10:47:06 pmThat is almost what I need. I may actually build something like that - but I think HMC363 has one disadvantage - it requires minimum -10dBm input power.Also divider like this is IMHO only useful for counters not so spectrum analysers. It simply divides the fundamental signal by means of Flip-flops and does not pass anything else, or maybe I am wrong?

author: Marco
author_rank: Super Contributor
timestamp: March 05, 2015, 11:20:07 pm
content: Don't Gunn diodes generally have more like +10 dBm output power?

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 05, 2015, 11:34:44 pm
content: Yes, true. Second limitation that comes from a fact that this is Flip-Flop like frequency divider that does not pass anything but fundamental signal makes it hardly applicable for my application. Speaking of parts from Hittite that may work here I think it is HMC787LC3B mixer.http://www.digikey.ca/scripts/DkSearch/dksus.dll?Detail&itemSeq=167866517&uq=635611734929123971&CSRT=7528028694163692216

author: Marco
author_rank: Super Contributor
timestamp: March 05, 2015, 11:52:44 pm
content: You said you wanted to measure the output frequency though, not the spectrum ... I thought the SA was a means to a cause.

author: Howardlong
author_rank: Super Contributor
timestamp: March 06, 2015, 12:00:30 am
content: As a matter of interest, what are you using the Gunn oscillators for? The last time I did anything with those was in the mid 80s, for a proof of concept for a high speed data link (in the 80s, 100kbps was high speed!).They were commonly used for radar speed traps, fabricated as a free running oscillator inside a waveguide cavity with a diode detector/mixer, and tuned with a couple of screws. They were difficult to stabilise due to temperature fluctuations, and back then trying to phase lock at that frequency was not trivial.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 06, 2015, 12:06:49 am
content: Quote from: Alexei.Polkhanov on March 05, 2015, 10:55:32 pm

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 06, 2015, 12:29:53 am
content: Quote from: Howardlong on March 06, 2015, 12:00:30 amIt is intended as part of a sensor in automatic door opener. I think if I will able to tune I will use it as powerful 10GHz test signal source.I know that most modern radars for these kind of applications use DRO-based oscillators with patch antennas.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: March 06, 2015, 01:34:29 am
content: Maybe this?http://www.qsl.net/n9zia/pre1/

author: edpalmer42
author_rank: Super Contributor
timestamp: March 06, 2015, 02:33:35 am
content: If your Gunn diode oscillator puts out +10dBm, you can use it as the LO for your mixer. Drive your 3 GHz sig gen at maximum level into the RF input and you might have enough 3rd harmonic at 9 GHz to give you a measureable IF output at 1 GHz. Bonus if you can high pass filter the sig gen output to remove the high level fundamental. I have an HP 8647A generator that only goes up to 1 GHz, but when I output +13 dBm I can easily measure a signal at 3 GHz.Ed

author: IconicPCB
author_rank: Super Contributor
timestamp: March 06, 2015, 08:29:12 am
content: Alexei,You could try to build a transfer oscillator. An oldie but a goodie.A step recovery diode is used as a comb generator. Drive the diode with a low frequency AF signal ( LO ).Mix with the 10GHz signal.Observe beat tones on an oscilloscope. Note the AF at whichadjacentnulls in the beat tones occur so You then know nth and ( n+1 )th subharmonic at which beats occur... and Bob's Your uncle.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 06, 2015, 02:57:52 pm
content: If he reads the Gunnplexor Cookbook he can do it with a Lecher Line. The shipping for a RF diode from Digikey will be about 15x the cost of the actual detector diode. :-)The advantage of the LNB is it is already built, broadband, costs 25$ and can be modified and running two hours after he gets it.Its also relatively level insensitive.If you go the prescaler route, you need a coupling network to sample the RF, which in this case is probably going to require some home made WR90 waveguide and a horn. By the time he buys a Prescaler, makes a board out of Rogers Teflon PCB (FR4 is nearly useless at 10 Ghz for a beginner) , learns how to tune a waveguide to SMA adapter etc... He's going to have a considerable amount of work to do. At that point he'd be better off to buy a used EIP Source Locking Counter and get it over with. He'd still need a 10 dB or 20 dB directional coupler to get the RF sample into the prescaler without major " load pulling "of the Gunn Diode's frequency.The prescaler's output is a sharp ECL edge, which is going to show as a huge pile of harmonics on the SA. So now he needs a counter, too.Another alternative is to locate an older radar detector beat the two Gunn diodes against each other... Older radar detectors have a detector diode that is biased by an 11.1 Ghz Gunn as the LO. In most cases you can easily walk the radar detector Gunn oscillator down to 10.5 Ghz. With some care he can then find where he's at with either the Lecher line or using harmonics from a 96 or 100 Mhz Clock oscillator module.Steve

author: rfbroadband
author_rank: Unknown
timestamp: March 08, 2015, 01:32:13 am
content: If your goal is to measure the frequency use a Hittite divider, like the HMC361 in combination with your SA.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 09, 2015, 10:44:28 pm
content: Thank you very much for suggestions guys.It looks like I do need a good mixer after all. I found some papers on a subject that pretty much explained everything, so once my mixer arrives I will experiment with it and perhaps will post my results. I do have WR-90 to coax adapter, no horn attached to it but I think I will be fine with adapter alone. I have attached the docs I was referring to. My SA does not have that external mixer utility on it, so I will have to make my own calculations and create in Excel or something like that. I believe that trickiest part is in calculating and setting right power for LO signal.

author: babysitter
author_rank: Frequent Contributor
timestamp: March 10, 2015, 05:35:28 am
content: As a ham who downconverted 10 GHz Amateur television to to SAT IF Baseband, I second the LNB suggestion. Violence to the ceramic resonator (grinding down the pill height or superglueing a second on top of it) allows frequency tuning.The single blocks with mixer and horn on one case work, but if you are really lucky, you can get very, very old stuff from the scrapheap maybe - where converter, polarizer, horn, polarisation couplers etc. are available as single parts that you flange-connect by their waveguide inputs/outputs.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 16, 2015, 01:47:30 pm
content: My fellow microwave hams have found a LNB that can be injection locked with a ~~27.5 Mhz signal allowing precise downconversion of the 10 Ghz band.See middle of this PDF:http://www.ham-radio.com/sbms/newsletters/2013nwsltrs/10sbms2013.pdfSteve

author: LaserSteve
author_rank: Super Contributor
timestamp: March 16, 2015, 02:18:09 pm
content: Stability hack for the LNB:http://f1chf.free.fr/LNBPLL/inside.pdfSteve

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: March 23, 2015, 06:45:40 am
content: I finally got my mixer.I think it turned out to be not that hard. I got a mixer on Ebay, looks new, but I was unable to find any info on it beside that seller provided - "Fr. Range 2 - 12 GHz"I am not sure how much power I can feed into LO. I started going up slowly and it worked with -6dBm. It has a removable cover - but inside there is another completely sealed box.Besides this unknowns I think it worked as I expected - I was able to look at signal from my Gunn oscillator at around 1.958 GHz or 1.96 ... I think my Gunn oscillator suck big way - frequency is jumping +- 500 kHz range like a rabbit. I have it powered with LDO regulator but still small change in input power make it change frequency by about 100-200kHz immediately.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 23, 2015, 01:15:37 pm
content: Is the Gunn current starved? Usually they like about 8 volts at as much current as the device will draw. Don't run the Gunn diode outside the cavity. Also make sure there is a bypass cap from the top of the Gunn diode feed to the cavity wall. Gunns will oscillate at VHF if the cap is not there, leading to instability.25-50 KHz jumps are the norm, and can be caused by feedback of RF into the horn iris. 100 KHz jumps are not unheard of.This is why people who use Gunns for ham radio use AFC circuits or try to injection lock the Gunn diode using a Bias Tee.Steve

author: LukeW
author_rank: Frequent Contributor
timestamp: April 08, 2015, 02:43:15 pm
content: To go back to your original question, the way I'd probably do it would be to take 3 GHz from the signal and build a 2x multiplier for that - an MMIC amp at an appropriate operating point, a filter for the 2x harmonic, and maybe another amplifier after that to give you a bit of signal level to play with.And then use that 6 GHz source as the LO input to the mixer.Alternatively, depending on what your tradeoffs are like (in terms of time, urgency vs money, effort, risk etc) you could buy something off the shelf, like these for example, and use them to generate the microwave LO.http://reactancelabs.com/store/index.php?main_page=product_info&cPath=2&products_id=5&zenid=b0a80c88ab174c834569a79ccb7c3f7dhttp://reactancelabs.com/store/index.php?main_page=product_info&cPath=3&products_id=2&zenid=b0a80c88ab174c834569a79ccb7c3f7d

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: April 09, 2015, 12:23:34 am
content: I think I solved the problem. At least I am moderately happy about the result. Also I made a video to share my experience: