[time-nuts] cheap GPS sim Re: Re: Another leap second problem

[Jim Lux]

 
Interesting - one would need an SDR with very good frequency accuracy and stability, if you're doing anything other than just checking GPS software.
That's part of what makes the commercial simulators expensive - in theory, they have good quality synthesis chains.

I'm not sure that the AD936x (used in most inexpensive SDRs as up/down converter) is of "time-nuts" quality in terms of the LO synthesis. Certainly one can feed in a good quality reference clock (derived from your H maser ensemble, disciplined by your set of Cs fountains, of course).  

At work, I have been fooling with a variety of cheap SDRs (real cheap - as in RTL-SDRs for $30-50) and they have all sorts of interesting internal compromises or settings in the synthesis chains which make no difference for their design purpose of receiving Over the Air TV broadcasts, but DO make a difference for other uses.
(I note as an aside, that there are people who claim to make multichannel receiver setups for direction finding, who seem unaware of the details of achieving phase coherence, even with common 28.8 MHz clocks)

On Sat, 8 Nov 2025 19:04:23 -0600, Steven Sommars via time-nuts <time-nuts at lists.febo.com> wrote:



GPS simulator: https://github.com/osqzss/gps-sdr-sim
Thanks for the pointer. [I see used Spectracom simulators on eBay for
$1000-$2000. This is above my hobbyist budget.]
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