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69293RXTX v6.3 improved signal to noise

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  • John
    Oct 14, 2012
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      I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer.
      On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.
       
      I have just tried this with the folowing result:
       
      With the two 10 Ohm resistors:
       
      Frequency 1.977 MHz
      With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
      With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -110 dB 
       
       
      Without the two 10 Ohm resisors:
       
      Frequency 1.977 MHz
      With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
      With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -104 dB
       
      This appears to have improved signal + noise / noise ratio by 6 dB
       
      Has anyone else tried this?
       
      John G3UGY
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