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1905Re: [dxatlas] "Skimmer Server" with QS1R Receiver

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  • Phil N8VB
    Apr 9, 2010
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      I would recommend using the Clifton Laboratories preamp if you find the sensitivity lacking with your particular antenna above 14-18 MHz. As long as you are not reaching the clipping level of the QS1R's ADC (+9 dBm), you do not need any bandpass filtering in front of the QS1R. The QS1R has more than enough sensitivity below 14 MHz with any reasonable antenna. If you find that when you add the preamp you are having trouble with clipping caused by broadcast stations, you will probably need to add some bandpass filtering or a high pass filter.

      A quick/inexpensive solution that works pretty well is to construct a 3 pole high pass filter with a cutoff of approx. 18 MHz and place it in front of the Clifton Laboratories preamp (I can provide the component values and part numbers). The HPF provides enough attenuation at the lower end of the bands to counteract the gain provided by the preamp.

      I have noticed some unusual behavior when I run Skimmer Server on Windows 7 64 bit - I'd recommend a system with XP if possible. Maybe Alex can say more about Windows 7 and Skimmer Server.

      Regards,
      Phil N8VB

      --- In dxatlas_group@yahoogroups.com, Wes Cosand <wes.cosand@...> wrote:
      >
      > Jeffrey:
      >
      > The QS1R has a large FPGA chip on the board. Alex has written code that
      > runs on the FPGA chip and creates the seven receivers. The signals are then
      > sent by USB to the computer where they are processed. So you have seven
      > continuous streams of data of up to 192 kHz each.
      >
      > In my hands the system has been pretty robust. The QS1R runs the rf from
      > the antenna almost directly into the ADC chip so there is no RF
      > pre-amplification. Consequently, it is a little insensitive, especially on
      > the higher bands. Since the front end is wide open, if you add lots of
      > pre-amplification and you are near broadcast transmitters, you get into IMD
      > problems. Some of us are using an 11 db preamp from Clifton Laboratories
      > which seems pretty good. Others are using pre-amps with a little more gain.
      > Clifton Laboratories also has a high pass filter for receivers with
      > broadcast band issues.
      >
      > I put the system on a Intel I7 computer running Windows 7 64 bit despite the
      > fact that this is not an officially supported OS. For reasons I do not
      > understand, the Skimmer Server application begins to report "CPU Overload"
      > and starts to decode only a fraction of the signals when I reach about 1100
      > simultaneous decoders. This is despite the fact that the machine and the
      > application are reporting only about 6 to 8% CPU load. I do not know where
      > the bottleneck is. This issue may be unique to my machine. Perhaps a 32 bit
      > machine would be better.
      >
      > Email me if I can be of further help.
      >
      > Wes, WZ7I
      >
      >
      > Wes Cosand
      > 6299 Route 413
      > PO Box 349
      > Pipersville, PA 18947
      > 267-864-6161
      > www.wz7i.com
      > CW Skimmer CQ spots: ve7cc.net:7333
      >
      >
      > On Fri, Apr 9, 2010 at 9:16 AM, jmaass_moose <jmaass@...> wrote:
      >
      > >
      > >
      > >
      > > How does the QS1R receiver with "Skimmer Server" provide up to seven bands
      > > at a time?
      > >
      > > Does it hop from band-to-band in sequence, or does it cover seven bands
      > > simultaneously?
      > >
      > > Who is using "Skimmer Server" with a QS1R? Good experience? Reliable
      > > hardware?
      > >
      > > We are planning an unattended installation of a Skimmer site on Curacao.
      > > We've been leaning towards what we've used before (multiple SDR-IQ
      > > receivers), but the QS1R is a more economical solution.
      > >
      > >
      > >
      >
      >
      > [Non-text portions of this message have been removed]
      >
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