[time-nuts] RAGA - was Re: Re: Low Phase Noise70 10 MHz bench signal source sought

[Lux, Jim]

On 4/2/22 9:42 AM, Tom Van Baak wrote:
> Yes, I believe hp did what you propose in their Santa Clara cesium 
> test lab. It was an ensemble of selected 10811 oscillators tightly 
> phase locked to improve short-term stability and phase noise. Rick 
> might know the details.
>
> During a tour I saw the instrument rack but was unable to peek inside. 
> Performance details were not given and I didn't get to count the 
> oscillators but I think it was on the order of half a dozen. I figured 
> that using 2 or 3 probably isn't worth all the effort. And using ten 
> or more is diminishing returns or maybe beyond requirements.
>
> You can imagine if you were allowed to select the best of the best 
> 10811's as they came off the manufacturing test line and then combined 
> a bunch of them as they did, the results would be quite impressive.
>
> If you develop a board for this I think it would be of interest to a 
> number time-nuts. It merely takes time to measure each oscillator in 
> the pile and pick the best ones. But combining them takes the tricky 
> circuit design that you are planning. Please keep us informed of your 
> progress.
>
> The concept of replicated simple electronics reminds me of:
>
> http://phk.freebsd.dk/raga/
>
> /tvb 

Separate email, because it's about RAGA..


I encountered a weird problem when I hooked up 4 OEM GPS modules to 4 
Beaglebones.. Side by side, they wouldn't all get GPS lock. It turns out 
the (unshielded) receivers radiate enough stuff to foul up adjacent 
receivers.   Move them several meters apart and no problems.  I didn't 
get around to seeing if there is some effect on the timing performance, 
even if they "get lock", but I'll bet there is.  At JPL we build 
multichannel (multiple RF channels) precision receivers, and this is 
something that is a problem (at least to the effect that we need to 
impose a crosstalk spec on the electronics chains).

I leave it as an exercise for the dedicated time-nut to decide how far 
to separate them before things like propagation non-isoplanarity, solid 
earth tides, and seismic effects, not to mention that since they're in 
places that are nanoseconds different, with the differences being SV 
related,  create a bigger problem than the "fail to lock"

When you get to "sub-meter" there's all kinds of interesting things that 
you have to worry about.  On some receivers, variations in delay through 
the LNA and bandpass filter and other electronics might vary nanoseconds 
over a 20C temperature variation.