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15214Re: AOR7030 vs Perseus on You Tube

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  • iv3nwv
    Jul 1, 2011
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      --- In perseus_SDR@yahoogroups.com, "Dominique Kremp" <dominique.kremp@...> wrote:

      > I bet the Perseus is able to bring a better signal with HDSDR or Winrad !

      I don't believe it so.

      Please, make the following example:

      1. Detach the antenna from your Perseus,
      2. Tune it to 9710 kHz/AM as shown in the movie,
      3. Set the DDC sampling rate to 125 kS/s,
      4. Select the 12 kHz bandwidth button and
      with the mouse wheel set the IF bandwidth to 6 kHz,
      5. Enable the the Main Average and set the slider so
      that the noise shown in the main spectrum gets smooth,
      6. Set the S-Meter in RMS mode to read the rms noise power
      in a 6 kHz bandwidth,
      7. Enable the Presel, disable the Preamp and Dither in the
      front-end control pane,
      8. Set the main spectrum span to 100 kHz,

      Now give a look to your Perseus window and compare it with
      that of the movie. They should look almost identical, with the
      difference that you won't be able to listen to radio Australia
      because in Step 1 you have detached your antenna from the receiver.

      Compare the reading of your S-Meter with that of the movie.
      Uh Oh! They indicate roughly the same S2 level, a bare -114 dBm level or so (if you open the software setting dialog and change the S-Meter units to dBuV it should now indicate a -6 dBuV level or so, that is 0.5 microvolt or so).

      Don't you find quite singular that your software is measuring in the same bandwidth the power which is measured in the movie where it is supposed that an antenna is connected to the receiver?
      An efficient antenna should exhibit tens dBs of noise excess at that frequency. Why it doesn't? Is it a short one? Has any attenuator placed between it and the receiver, was this due to a badly isolated or faulty antenna splitter either he took the movie just during an exceptional day in which our galaxy didn't emit the noise we expect to receive from?
      I'm sure that IK1QLD would like to comment this further.
      He should also be able to explain why in his movie the audio that comes out the AOR7030 sounds much better than that of Perseus.

      Btw, it's just matter of the difference of the two receivers noise figures, 9 dB for the AOR7030/Preamp ON and about 9 dB more for the Perseus.
      If the sky temperature seen by the antenna were 300 K, as it looks in the movie, you would get 9 dB more SNR from the AOR7030.
      But you would need a very inefficient antenna to get such a difference, either placing an 20 dB attenuator between it and the two receivers.
      Efficient short wave antennas see a much higher sky temperature: for a 20 dB excess noise which is the minimum value that one can expect up to 20 MHz or so, the difference in sensitivity would be negligible but the dynamic range of the AOR7030 with its preamplifier would be much lower than that of Perseus.

      Nice to see that nowadays anyone can (coarsely) measure noise figures with new RF instruments like You Tube :-)

      Nico / IV3NWV
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