Also see http://www.ke5fx.com/gunnpll.html , a quick and dirty but successful attempt at locking a Gunnplexer in a relatively low (1 kHz) loop bandwidth. The inband noise is likely too high for good performance in a radar application, but the basic idea is workable enough. Unfortunately I tried this experiment before I had any way to generate log plots. :(
I can't think of many noise-critical applications where a microwave VCO is used without some form of phase locking. I'd think that a homodyne architecture would still need a synthesized source, just because the waveform being received is delayed relative to the one that was sent. Without a clean source, I'd imagine that you'd have to do autocorrelation between the outgoing and incoming channels rather than simple/cheap baseband mixing. An obvious question would be whether it's cheaper to add another digitizer and correlator to your pipeline than it would be to clean up your source... -- john, KE5FX Miles Design LLC > -----Original Message----- > From: time-nuts [mailto:[email protected]] On Behalf Of Magnus > Danielson > Sent: Wednesday, June 17, 2015 1:08 PM > To: [email protected] > Cc: [email protected] > Subject: Re: [time-nuts] Close in phase noise of microwave VCOs > > Jim, > > John Miles have been a bit active: > http://www.ke5fx.com/brick/brick.htm > > Just to give you a start-sample. > > Cheers, > Magnus > > On 06/17/2015 05:22 PM, Jim Lux wrote: > > I'm looking for some representative data for inexpensive microwave VCOs > > (in the 2.5-6 GHz range, in general). Not in a locked loop situation, > > but just bare: with a DC voltage on the tuning input. I'm particularly > > interested in data closer than 100 Hz. > > > > Most of the data sheets (e.g. from Minicircuits, ROS-3710; crystek > > CVCO33 series) show noise from 1 kHz or 10kHz out, because most of these > > parts are intended for use in a PLL, and the "close in" will be > > determined by the loop. > > > > Before I go out and hook one of these up and measure it, I figured I'd > > ask if someone out there has done it, or if there's a data sheet. > > > > I'm not looking for any particular part or frequency or even exact > > numbers: more "representative, typical" kind of performance one might > > get from one of the plethora of $20-50 VCOs out there. > > > > Something like the ROS-3710 looks like it's about -30dB/decade trending > > to 20 dB/decade. > > (-70 @ 1 kHz, -96@10kHz, -118@100kHz, -138@1MHz) > > > > A paper I found on 77 GHz sources cite a 30dB/decade (actually they give > > it as f^-3.05). > > > > > > > > > > background: > > > > I've got a homodyne radar at work we use for detecting heartbeats of > > buried earthquake victims. I've also got a variety of gunn oscillator > > "doppler radars" of one sort or another. > > There's 10GHz homodyne radars available for $5 from China (the selling > > prices range from $1 to $20, with corresponding inverse costs in > > shipping.. ). They're designed for intrusion detectors and automatic > > door openers. > > > > There's all kinds of cheap 2.45 GHz sources around: one might be able to > > repurpose an old 802.11b WiFi interface, for instance, although I think > > those are all synthesized PLL designs. > > > > And my car has a 77 GHz radar in it for adaptive cruise > > control/automatic braking. > > > > There's also Greg Charvat's "build a SAR with coffee cans and a laptop" > > mini-class/dissertation project. > > > > RF wise these radars are simple device, and I was asked to give a > > presentation to the JPL Amateur Radio Club on the principles and > > limitations on performance. Most of the members of the JPLARC (like me) > > actually know quite a lot about RF design, so they'll be asking about > > "what about the phase noise of the Tx". We all know, qualitatively, > > that gunns are noisy close in (to the bane of hams who want to do narrow > > band stuff with the old MaCom gunnplexers), although, like with the > > minicircuits VCOs, there's no published data on their 1-100 Hz phase noise. > > > > So I'm writing up a set of notes on the various factors, and the self > > noise of the oscillator is particularly important when looking for low > > frequency modulations (like heartbeats at 1 Hz, or people walking). > > > > I've got empirical "as measured in the system" data from my 3GHz > > homodyne radars, but I was looking for some component data as an example. > > > > > > Actually, if someone has some close in data from a 10.525 GHz Gunn (or > > the newer motion detectors), I'd love to see that too. > > > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time- > nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
