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Fw: Fw: Re: [softrock40] Re: Bandpass filter smilter

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  • windy10605@juno.com
    On the other hand, I tried SR-40 V4.0 and Rocky with a BPF for 80m, then switched to direct (no BPF ahead of T1) and could see no notable difference at
    Message 1 of 1 , Jan 30, 2006
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      On the other hand, I tried SR-40 V4.0 and Rocky with a BPF for 80m, then switched to "direct" (no BPF ahead of T1) and could see no notable difference at various points of the 80m band with the "no BPF" frontend  .....you would think 7-8Mhz would be all over the place.
      With a little pin "swizzling" you can connect the Mini-Ckts T1-1T transformer for T1. It's spec says 1dB insertion loss from 0.8Mhz to 80 Mhz and a 3dB insertion loss from 0.08Mhz to 200Mhz. ........that's a pretty good range for a cheap RF transformer.
      73 Kees K5BCQ
      ----- Forwarded Message -----
      Date: Mon, 30 Jan 2006 13:42:11 -0600
      Subject: Fw: Re: [softrock40] Re: Bandpass filter smilter
      OK, good point Art. They --do-- respond to harmonics and I can see how this would be a really serious problem for using it as an LF receiver design.
      73 Kees K5BCQ
      Date: Wed, 01 Feb 2006 14:15:03 -0500
      Subject: Re: [softrock40] Re: Bandpass filter smilter
      Good observation Joe, you discovered the Achilles Heal of the
      softrock type detectors! Although it's not a serious problem, you
      have to be aware of it and limit front end filters response to
      appropriate values.

      The ratio between the lowest frequency passed by the front end filter
      and the highest frequency passed cannot be more than two to one-for
      exactly the reason you describe.

      It responds to harmonics.

      Several have thought of using the softrock for VLF and ULF receivers,
      say from 2 KHz to 80 KHz. And, of course they run into the same problem.

      2 KHz to 4 KHz is ok, 4 KHz to 8 KHz is ok.......but don't try 2 KHz
      to 8 KHz without separate filters for eash 'band'.

      GL to all.


      At 11:46 AM 2/1/2006, you wrote:

      >  When I first received my SR40 I
      replaced the input transformer
      >with a wide band transformer made by
      RELCOM. I was using a DDS board
      >to supply the Xtal input with the idea of
      just using bandpass or
      >lowpass filters ahead of rx. to cover a large
      frequency. It seened to
      >work ok at hf frequencies but when i tried it a
      LF 200-450khx I
      >received a lot of broadcast stations that i didn't have
      with my
      >superhet SD40 as sugested by wa6ufq. Further testing revealed
      >following problems.
      >Strong spurious response at odd
      multiples of the receive fqequency
      >3x,5x 7x as a example when tuned to
      300khz receiver would respond
      >to 900,1500,2100khz ect. now you can see
      why i was hearing strong
      >broadcast stations at LW.
      input transformer I used i rated to 50khz, maybe my receiver has
      problem but phase and balance look good.
      >I also checked another SR40 at
      10mhz it also could hear 30mhz.
      >Another problem the shows up is
      automatic phase and balance changes
      >when changing bands such as going
      from 40 to 20 mtrs. Not a concern
      >if this data can be stored for each
      >Can you please verify the above on your
      >Thanks Joe
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