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.
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