[time-nuts] Close in phase noise of microwave VCOs

Magnus Danielson magnus at rubidium.dyndns.org
Wed Jun 17 16:08:13 EDT 2015


John Miles have been a bit active:

Just to give you a start-sample.


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 at 10kHz, -118 at 100kHz, -138 at 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.
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