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55914RE: [softrock40] Re: Softrock sensitivity.

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  • Martin Sole
    Jun 1 10:49 AM

      I tried 4.7k for R7 and R8 but my opinion is that it is too much and compromises the performance though the gain is about the same as the 20m 6.2 TXRX. With the 1k resistors and using Rocky I need to add about 18dB offset to the S meter for S9 at -73dBm.

       

      The next bit of your message Alan got a bit confusing. You said 1mV, Graham said 1 uV. Listening again t sounds like it could certainly be 1mV!

       

      1mV is -47dBm. Adding 27dB attenuation would be -70dBm, still huge. If you meant 1uV that’s -107dBm adding 27dB attenuation would be -134dBm, that’s weak 0.045uV, way more than I need.

       

      4.7k resistors give me about 6dB SINAD for a 1uV (-107dBm) input. Putting them back to 1k drops that to about 4.5dB but with a flatter noise floor. A resonant 40m antenna gives about a 7 to 10dB increase in noise over nothing connected so now I’m starting to wonder if I really do have a problem. Think I am going to have to rig something up using the Orion as a reference and see what that sounds like in comparison. Could well be all for naught but still my audio does not sound as strong as Grahams signal if that was 1uV.

       

      Martin, HS0ZED

       

       

      From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On Behalf Of Alan
      Sent: 01 June 2011 22:09
      To: softrock40@yahoogroups.com
      Subject: Re: [softrock40] Re: Softrock sensitivity.

       

       


      ----- Original Message -----
      Subject: RE: [softrock40] Re: Softrock sensitivity.

      > No, I'm building the Lite II for 40. The early version seems to show 1k
      > but
      > Tony's later drawing shows 4k99. I have 1k fitted as per Jan's kit,
      > sooooo,
      > what's it to be, 1k or 4k99?
      >

      In that case, 1K.
      BUT this is to reduce the gain.
      Tony reduces gain on the lower bands by increasing R5/6, effectively the
      same.
      Please try this with an antenna. See how it actually works. can you compare
      it with something else?
      I found my 1mV source, tested it with my AR7030 on 5MHz. It sounded like
      Graham's MP3.
      I could still hear it with 27dB attenuation of the 1mV.
      the 5MHz band at midday in the summer is at it's quietest. When I attached
      an antenna I reckoned the noise was about 6dB below the unattenuated 1mV
      source.
      Now his is not with a Softrock but it shows my AR7030 was far too sensitive
      as I had set it.
      Striving for the ultimate MDS is irrelevant on the lower frequencies. It
      just reduces dynamic range.
      If you do think you need more gain you could put 4K99s in and see what you
      think.

      73 Alan G4ZFQ

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