[amsat-bb] SDR transmitter asa Doppler dig-gen

[Norm n3ykf]

Much easier to use an HP signal generator and drive it via the GPIB
port. Less noise, more accurate, etc..

A nit to program across GPIB. Slightly more complex than talking to a TNC.

Norm n3ykf

On Mon, Apr 17, 2017 at 10:37 AM, Robert Bruninga <bruninga at usna.edu> wrote:
> Some students built an HF inverting SSB transponder simulator.  (4 diodes,
> and a siggen at 58 MHz) so they can then use two FT-817’s on the 21.4 MHz
> uplink and 29.4 MHz downlink) for our next satellite:
> http://aprs.org/hfsat.html )
>
>
>
> Now we want to use an USRP 2922 SDR as the programmabel oscillator around
> 58 MHz so we can simulate Doppler.
>
>
>
> Can anyone whip out some code to make the oscillator follow a Doppler Ramp
> in freuqncy from say 58.100 to 58.900 MHz over a ten minute pass.  That
> should be easy enough for one-observer.  Can just be linear for now
> (simulating a low pass).
>
>
>
> But then once that is done, we need the driver to then FLIP the Doppler
> shift instantly in the opposite direction to simulate the shift seen by
> another observer at the other end of the pass.  This is another layer of
> complexity, but we will simply have a push button input to shift between
> the two states when one station or the other is transmitting.
>
>
>
> But for now, the students just need some handholding to get the basic SDR
> acting as a signal gen at 58 MHz and how to input the freqncy ramp to it.
>
>
>
> Thanks
>
> Bob, WB4APR
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