[hpsdr] QSD gain and noise.

[FRANCIS CARCIA]

I have found a fair amount of noise comes into the unbalanced inputs is due to Radio shack audio cables. I use 12 feet, 2 six footers spliced with an adapter.  My set up has a noise floor down around -140 dBM until I connect the cables with the converter turned off. Then the noise comes up about 8 dB or so. My SDR converter is hanging off the 455 KHz output of a RA6830 DF radio so I just run the gain up high enough to overcome this noise. The OP amp gain in my setup a copy of the Flex converter is hard wired to X10 or 20 dB. I would think the gain could be X2 or X3, 6 to 10 dB to get a good noise floor with the HPSDR set up. I would think the Flex at MW would have similar performance as my set up at 455 KHz.
  Guy, you might look at your inerface cables as a possible source of a high noise floor. Maybe you could use RG58 shield over your cables terminated at one end only. I have a lowfer friend who likes CAT 5 cable for balanced runs. 
  My jumpers are not installed and have not changed the series resistors to balance the gain since I have plenty of signal drive level. frank 
   
   
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