Ordering GPS clock for maser work
andrew....@googlemail.com
This is the external clock I have purchased – I believe it has been recommended several times on this mailing list in past and has advantage of producing correct voltage and being very flexible, and being set by GPS constantly so very accurate.
LBE-1420 GPDSO locked clock source from Leo Bodnar https://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=107&products_id=393
One question I would like to ask members of this group – conceptually, can two telescopes using these clocks be run disconnected from each other, both observing same target (say the sun) and saving data locally – perhaps using SDR#; and then later the data combined in analysis – e.g. on Excel values at same GPS time-stamp on data (from GPS clock source on each telescope) added or multiplied – to generate interferometry results which will show the typical interferometry trace as sun passes through the beam of the radio telescopes? Would that work without the telescopes being physically linked, without them sending data to the same computer during collection?
Andy
Stephen Arbogast
Marcus D. Leech
quite well, the devil is in the details. They will have phase noise that is mutually uncorrelated, and therefore the correlation of two such baseband streams will
generally be uncorrelated as well. The correlation, averaged over a few 10s of seconds won't be zero, but it will have a considerably lower SNR compared to
two receivers that are in effect sharing a single clock. Indeed, you could have a "master clock" for a receiver pair that is relatively crappy (cheap XTAL), and it would
still produce quite-decent correlation results, because both receivers are "zigging and zagging" in perfect synchrony with one another.
I've measured GPSDOs in the lab many years ago--they were sharing a single antenna. They didn't usefully agree on their fine-scale phase noise. I wrote a simulation years
ago that demonstrates this. The correlation SNR plummets precipitously as the mutual phase-noise increases.
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Stephen Arbogast
Andrew Thornett
Sent: Monday, 20 July 2026 23:17:25
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] Re: Ordering GPS clock for maser work
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Stephen Arbogast
Stephen Arbogast
Marko Cebokli
To see, if you can do interferometry, as a course criterium, you can use the lambda/8 rule for telescope mirrors. Converted to phase/time, it means you must keep within 45 degrees of phase. This gets proportionally harder, as you go higher in frequency, since 45 degrees equates to less and less nanoseconds. Long term drift will limit the maximum integration time you can use.
A good (!) GPSDO would be suitable for interferometry on HF (like 20MHz Jupiter or Sun), and maybe for lower VHF. For the 21cm line, no way. Note that all GPSDOs are NOT created equal, far from that!
A few years ago, I did some measurements on various OCXOs and GPSDOs. As is true with all of my projects, this is also a perpetual work in progress :-) It includes some common antenna GPSDO tests:
https://lea.hamradio.si/~s57uuu/mischam/tenmp/index.html
I also tested the GPSDO performance with different antenna locations (sky coverage) and tried to analyze diurnal variations, while experimenting with developing a GPSDO myself:
https://lea.hamradio.si/~s57uuu/mischam/gpsy/index.html
Did play a little with rubidiums, but will have to do more work on them, to know them better.
https://lea.hamradio.si/~s57uuu/mischam/rub/index.html
In the mean time, I have moved, and have no access to the roof at the new place, so can't locate the GPS antenna optimally, and such work is currently stalled.
Marko Cebokli
21.07.2026 00:17, je Marcus D. Leech napisal
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