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69302Re: [softrock40] RXTX v6.3 improved signal to noise

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  • Alan
    Oct 15, 2012
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      ----- Original Message -----
      Subject: Re: [softrock40] RXTX v6.3 improved signal to noise


      >Those 10 ohm resistors before the mixer are dropping precious nanovolts of wanted signal. Worsening signal to noise ratio.

      John,

      It does not seem that simple to me.
      My initial thought was "After many years of Softrocks how could this be?"
      6dB is a big difference.
      From a practical point of view with a Softrock connected to a good antenna what difference will it make?
      On a sufficiently sensitive low noise receiver SNR is established at the antenna input. Signal/atmospheric etc. noise. Provided the
      receiver adds no noise the SNR is fixed. Indeed with the lower frequencies an attenuator can be used with no effect on SNR. Tony
      uses attenuators in the Ensemble RX.

      Now, maybe on the higher frequencies a Softrock might need to be a little more sensitive. I understand this is sometimes done by
      using a low noise card and reducing op-amp gain. So why, apart from Tom, has nobody suggested removing the resistors?
      What are they doing? Is there something else that is degraded if they are removed? Are they an integral part of the mixer?

      73 Alan G4ZFQ
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