I have modified freedv_tx to output VCO frequencies for the 2400A and
800XA modes:
Example 1:
./freedv_tx 2400A ../../raw/hts1a.raw - --extvco | hexdump -v -e '/2
"%04d\n"'
3600
3600
1200
3600
1200
1200
1200
4800
<snip>
Example 2:
./freedv_tx 800XA ../../raw/hts1a.raw - --extvco | hexdump -v -e '/2
"%04d\n"'
1200
1600
1200
2000
1200
2000
1200
0800
<snip>
The output is 16 bit shorts with the frequency in Hz of each tone. The
output sample rate is the symbol rate, so 1200 symbols/s for 2400A, and
400 symbols/sec for 800XA. The sample rate needs to be throttled by the
"data sink" DAC.
The use case is transmitting the FreeDV FSK modes with external FM
transmitters, for example off the shelf VHF/UHF radio with "data port"
input. The DAC could be an Arduino or similar.
I've messed around a bit sending 2400A from my FT817, I used a stm32
Discovery board as the DAC.
- David
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