Thursday, 17 September 2015

SSB using DATV-Express

DATV-Express TX SSB/FM Application

Just a quick preview of a small application I have been working on that turns
DATV-Express into an SSB/FM transmitter. Originally I used a couple of FFTs
to do the IQ generation, filtering and interpolation. Now inspired by
Dave, W9GR's article in QEX on CESSB (Controlled Envelope Single Sideband)
I use the Weaver method of SSB generation combined with  his clippers.
I currently interpolate the output signal by 16 to 128 KSamples per sec using
halfband filters before sending that to the DATV-Express board via USB2.
On the Express board the signal is further interpolated by a factor of 64 to reach
the final sample rate.

The high sample rates is required because DATV-Express has fixed 5 MHz LPFs
for anti-aliasing, after all it was designed for digital TV rather than narrowband SSB.

The RF level sets the output level of the DATV-Express board and the AF level
sets the input audio level from the PC's microphone.

The application still has some rough edges. I wrote it so I could have something to
drive the 10 GHz transverter I have built  which requires an IF of 1 GHz.
The transverter  uses a  9 GHz YIG based oscillator for its LO.
For receive any number of cheap SDRs could be used.

The processing overhead is relatively low, I am hoping it will be low enough to run
on the Pipo X8. Something I will try later today.

For those unfamiliar with DATV-Express, it is an exciter board that produces
around 10 dBm output which will transmit anywhere from about 65 MHz to
2.48 GHz. The board has been designed for the generation of digital TV on
Amateur Radio frequencies.

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