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

[Zach Leffke]

agreed.  Phase noise and such will be much better from HP products.

If thats the setup scenario, could still use pyephem married up to the 
driver code for the GPIB interface to generate the doppler profiles.


-Zach

Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

On 4/17/2017 12:37 PM, Norm n3ykf wrote:
> 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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> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
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