[time-nuts] Re: Eloran long test from now to August or September.

[Jim Lux]

I’ve experimented with just this idea - injecting a pilot tone, with modulation.  I was contemplating building an interferometer with surplus Ku-band dishes/LNBs, so there’s no easy way to phase lock the front end.

I did it with 4 RTL-SDRs, and I’ll scrounge up the measurements.    My first attempt was just to couple the 1pps from a GPS module into the inputs - that’s not easily detectable (I was hoping that the fast edges would be sufficiently broadband to be detectable in the sampled data stream - nope..)

Next was an in-band tone from a 10 MHz oscillator.  It’s easy to recover the narrow band tone, and if the level is appropriate, it’s easy to adaptively subtract it from the sampled data.  

My next strategy was to put a BPSK modulated tone (at a low rate), and I never got that one to work right - whether because my lash up modulator wasn’t right, or because of software problems.  It should be easy to recover, to recover the chip and carrier phase, etc.  If one ran the PN generator at an exact divisor of the tone, that would probably help. 


On Tue, 26 Sep 2023 10:18:43 -0400, "Lester Veenstra" <m0ycm at veenstras.com> wrote:

This may out of scope for most users of the RTL-SDR but if you have a local GPSDO time / frequency source, you might consider a coupled injection of a local modulated signal that can be used to time stamp the output bit steam to the required precision, and then sample time derived from the marker detection, assuming the sample clock is stable enough until the next injected (out of band) local. The injected calibration signal could be as simple as a A1 carrier transition, on up to a time synced spread spectrum underneath the noise gloor.

Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)
lester at veenstras.com

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-----Original Message-----
From: Jim Lux via time-nuts [mailto:time-nuts at lists.febo.com]
Sent: Monday, September 25, 2023 11:10 AM
To: time-nuts at lists.febo.com
Cc: Jim Lux
Subject: [time-nuts] Re: Eloran long test from now to August or September.





The challenge is that most inexpensive SDR modules do not provide the time stamping of the ADC. They’re more a RF to stream of samples device.


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