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Speculations about Skimmer in Multi-Op Situations

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  • Pete Smith
    There *may* be a couple of issues affecting potential use of Skimmer by a multi-transmitter station. I emphasize the may because I don t have the means to
    Message 1 of 2 , Sep 24, 2008
      There *may* be a couple of issues affecting potential use of Skimmer by a
      multi-transmitter station. I emphasize the "may" because I don't have the
      means to test these scenarios, and I'm wondering if other members of thius
      list can shed any light on them.

      The first is decoder upsets from strong local signals on the band the
      Skimmer is listening on - it seems to take a second or so between the time
      strong signals stop blocking the receiver front-end and the time that the
      decoder resumes decoding properly. If a station has antennas for in-band
      S&P listening, my original thought had been that those could be used for
      the Skimmer, with a simple multi-coupler or passive splitter. However, a
      friend recently suggested that a lot probably
      depended on the use of narrow CW filters by the S&P radios, and that the
      inherently wideband SDR front ends might still be clobbered by transmitted
      signals. If that's true, I'm thinking that multis may not get the Skimmer
      payoff they'd hope for - with 3 seconds or so between CQs on the run radio,
      a 1+ second decoder recovery time would cut substantially into Skimmer's
      listening time.

      The second issue has to do with computer loading from the flow of
      spots. Because Skimmer re-spots each station that it is still hearing
      every ten minutes, the volume of spots from each Skimmer could be very
      high. As an example, during the SAC this past weekend I was receiving well
      over 100 spots on 20 per 10 minute period. Now multiply that by several
      bands open at once during the night, and there is some question how well
      the logging software can manage the load of receiving the spots and
      populating the various bandmaps. Filtering to allow only spots on the
      desired band to populate the bandmap on each computer may be the solution
      to this.

      73, Pete N4ZR
    • Marijan Miletic
      Main SDR problem is ADC overload as useful data are lost. PC sound card has about 100 dB dynamic range and line-in input should survive inband strong signals
      Message 2 of 2 , Oct 5, 2008
        Main SDR problem is ADC overload as useful data are lost. PC sound
        card has about 100 dB dynamic range and line-in input should survive
        inband strong signals which are not controled by narrow RX AGC loop.
        Local TX in M/M environment should be eliminated with decent RX BPF.
        Skimmer recovery time from local inband TX is very fast and bandmap
        filling between CQs works. It is up to contest software to manage
        large number of Skimmer posts. N1MM Logger with Access database does
        it fine. Only visual display gets overcrowded. My experience is based
        on FT-1000MP SDR on both RX 455 kHz IF in busy CW contests.

        73 de Mario, S56A, N1YU
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