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Softrock as IF subsystem

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  • bofh47
    I ve completed installing a 9mHz softrock into my old Ten Tec Argosy, sampling the IF just after the post-filter amplifier. The softrock is mounted in place of
    Message 1 of 1 , Nov 27, 2006
      I've completed installing a 9mHz softrock into my old Ten Tec Argosy,
      sampling the IF just after the post-filter amplifier. The softrock is
      mounted in place of the useless Noise Blanker board, and power
      switched from the "NB" front panel switch. I replaced a triple
      phono-jack "accessory" strip on the back panel with three small stereo
      jacks, for IF Out to the soundcard, Audio In from the soundcard, and
      paddles (for a built-in keyer). A switching transistor across the
      "enable" pins on the softrock is toggled from the "Receive" line in
      the Argosy, to take care of muting during transmit.

      I also built a little FET audio switch to allow the NB-switch voltage
      to also select the input source for the audio chain. That way, during
      SDR useage, I still get sidetone and audio output at the phone jack
      and internal speaker, and with the NB switch "off", the radio performs
      normally.

      The IF passband was very obvious on the spectrum display even without
      an antenna, as a sharply-defined area of increased noise a few kHz
      wide. I set Rocky's tuning for the midpoint of the passband and left
      it there, doing all subsequent tuning with the main tuning dial of the
      Argosy. I had to use a second receiver to find the correct RIT offset
      to put my transmitted signal back onto the received frequency for
      proper transceiver operation (this offset comes from Rocky tuning, the
      softrock clock frequency, and the transceiver CW offset).

      I finished it in time to try it out in the CQWW DX test this weekend,
      and it was an interesting experience (although mostly I used my old
      Drake twins). It worked rather well in the context of a transceiver,
      and tight dsp-derived filtering was very helpful to hear the DX
      stations through the loud US callers. The displays, especially the
      waterfall mode, were particularly useful when using a narrow passband,
      to stay aware of loud nearby (but inaudible in the passband) signals.
      Switching and processing delays were not as problematic as I expected,
      in terms of supporting full break-in. If I couldn't hear between
      high-speed dots, at least I could certainly hear during longer gaps,
      and it was definately better than the VOX-derived "QSK" provided by
      most transceivers.

      I used Rocky, and found an item for a "wishlist": an easier way to
      rapidly adjust the passband width. Easy-to-mouse large buttons or a
      large slider (not near the tuning area) would be nice, or better yet,
      a keyboard alternative (perhaps some configurable keys?).

      I'll put more mileage on it in the coming week or two, but I'm quite
      pleased with it so far.

      Neil
      KX2Y
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