Tuesday, December 24, 2013

A-B Board SDR

The mixer and amplifier sections of the B board were populated.  The amplifier supply was errantly captured in the schematic as +3.3V and should have been +5V.  A trace cut and white wire corrected this.  A 19 inch 30AWG wire attached to an SMA served as a simple antenna.  There are no image rejection filters and no low noise pre-amplifier.  This leaves the noise figure no better than the first stage BGA2866 amplifier at ~3.8dB and doubles the mixer NF by allowing the image noise.  All things considered this is working quite well.

The following video captures using the A-B board combination with SDR-Console (previous SDR captures used an external LNA and down converter with the A board only).  The console has not been calibrated in dBm so only relative comparisons are valid.  Several local broadcast FM stations are covered including their RDS and demodulated FM spectrum.  In addition, the local narrow band NOAA weather broadcast is shown.  The upper left xterm is a "top" session running on the BBB showing CPU use (the radio application is dev-pru).  The lower left xterm is the console output of this application.  The running output is the complex sample rate.  The ADF4351 programming debug is also enabled and visible on tuning change.

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