[hpsdr] More J/O testing with homebrew QSD

[FRANCIS CARCIA]

Tonight I did some dynamic range testing the old fashion way. I didn't have the RMS volt meter on the audio so played it by ear. Two generators were HP8640B with a homebrew combiner. Cf 455 KHz, color burst crystal source /8
  Spacing           Dynamic Range at mds
   
  500 Hz.             80 dB
  1 KHz               90 dB
  5 KHz               95 dB
  10 KHz              97 dB
   
  Now this blows away the detector of the RA6830 for close in dynamic range. I'm going to build a new front end with a RA6830 first mixer and modified RA6840 second mixer. The First mixer can handle the 8640B wide open (+19 dBM) and just appeared to start compressing but I didn't stay there long because I was afraid of blowing the roofing filter. The second mixer is a special that measures 105 dB of dynamic range at 10 KHz signal spacing. These two mixer modules will feed the homebrew Tayloe QSD. The total gain ahead of the Tayloe will be about 10 dB.I do notice something with the software when I do 10 dB steps with the generator off frequency. There seems to be a wide blank of audio. I also notice a similay problem when QRN is high.  A few weeks ago on 160 meter AM. The 6830 was making usable audio while SDr was only making noise. This front end will do about 100 dB of dynamic range at 10 KHz but not sure how the synthesizer will act very close in. I will have 2 6 pole 20
 KHz roofing filters. one in each module. 
  It will be interesting to see how far this performance will go against an A/D hanging off a preselector. Frank
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