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Re: [PNWVHFS] Re: Receiver MDS calculations at home

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  • Bill W5WVO
    Ed, I take your point. Something in the test setup has to be accurately calibrated, and that would be the signal generator and the attenuator chain. The
    Message 1 of 1 , Apr 29, 2008
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      Ed, I take your point. Something in the test setup has to be accurately calibrated, and that would be the signal generator and the attenuator chain. The measurement device on the back end measures relative signal (noise quieting) so its absolute accuracy isn't at issue. The nice thing about doing your own MDS measurement is that you can set the receiver up just the way you're going to use it, as opposed to the test lab's "standard" configuration, which is intended to compare one receiver (on the bench) to another receiver (on the bench).
       
      Guess I'll look into less-expensive signal generators and see what their output voltage accuracy is claimed to be. :-)
       
      Bill W5WVO
      ----- Original Message -----
      Sent: Tuesday, April 29, 2008 8:50 AM
      Subject: [PNWVHFS] Re: Receiver MDS calculations at home

      Bill,

      I have made this test on my 2m eme system and receiver (stand-alone).  I don't see how you can avoid having a known signal level source (e.g. calib, signal generator).  Then a standard way of measuring signal and noise.  For SSB/CW this has been the signal quieting standard using an audio voltmeter.  For FM, SINAD is the industry standard but hams probably still use signal quieting.  One also needs a set of calibrated RF attenuators to get those weak signals.  MY signal generator would provide -130 dBm min so adding a 60 dB attenuator got things really weak!  Double shielded coax is necessary to keep unwanted radiation leakage into the receiver.

      I recently went thru this process to determine the MDS for my SDR-IQ/IFAmp/DEM 144/28-xvtr set up.  JT65 offers a nice way to measure signal level as an alternative to the audio voltmeter.  The waterfall + signal level reading makes comparisons easier (SSB mode).  For digital modes BER, etc. I haven't any good advice.

      You can view my SDR testing screens and power-point presentation to CSVHF on my web:
      http://www.kl7uw.com/SDR.htm

      *****************************************************
      73, Ed - KL7UW              BP40iq, 6m - 3cm
      144-EME: FT-847, mgf-1801, 4x-xp20, 185w
      http://www.kl7uw.com      AK VHF-Up Group
      NA Rep. for DUBUS: dubususa@...
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