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KGKSDR build 40 released (CW TX)

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  • Duncan Munro
    KGKSDR build 40 has been released to the website download area at: http://www.m0kgk.co.uk/sdr/download.php This has a facility for cancelling the opposite
    Message 1 of 1 , Nov 27, 2006
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      KGKSDR build 40 has been released to the website download area at:

      http://www.m0kgk.co.uk/sdr/download.php

      This has a facility for cancelling the opposite image, and a fledgling
      CW TX capability and I will try to describe the new features in this
      post as the help file has not been updated yet ;-)

      NEW OPTIONS

      Under options > transceiver there are a couple of new items on the
      hardware tab. On the ports panel, you can set the com port for the
      four pins that connect the PC to the outside world.

      * Morse key: Key in normally CTS.
      * PTT in: DCD but can be also be CTS (not implemented yet, will be
      used as PTT for SSB).
      * Common high: DTR. This is a voltage source point to power morse key
      and ptt button (more later).
      * PTT to TX: RTS. This is the TX/RX line to control the Softrock.

      Wiring up. RTS goes straight to the Softrock as described above. The
      DTR line is set by the software to a positive voltage (measures +9V on
      the port here). This can be connected via a 4.7K pullup resistors to
      the morse key input and/or PTT input leaving them floating at 9V to
      12V when the contacts are open. If you are using an external keyer it
      should be fine with this arrangement.

      IMAGE CANCELLATION

      From the options menu, select "Set TX manual cal point..." which will
      bring up the calibration screen.

      Hit the TX on box and you will start transmitting a continuous
      carrier. Note that the status bar on the main screen goes dark red
      when you are transmitting.

      The idea with this screen is that you output a tone and the screen
      will tell you where the image is likely to appear. Using a different
      receiver, you monitor the image frequency. Using the S meter and your
      ears, you play around with the amplitude and phase adjustments until
      the image disappears in the mush.

      Hit the 'save point' button and move onto a different frequency.
      Repeat the process until you get bored (12-20 points is probably enough).

      The frequency slider takes you close to the + and - Nyquist
      frequencies and various frequencies in between.

      The amplitude and phase controls are each in two parts. The left-hand
      control moves the values up and down, and the right-hand control acts
      as a zoom function allowing you to access finer resolutions.

      Start off on coarse settings and spin the amplitude and phase looking
      for a dip in the image. Repeat if required. Move the zoom controls
      to the right by one click to get finer control and play around with
      phase and amplitude again.

      With a bit of practice you should be able to null the image quite
      quickly. A bit of advice: don't bother chasing your tail by trying to
      get -120dB image rejection. If you cough, or the line voltage changes
      the image will jump back again and you will never achieve perfection.
      You will get very frustrated, don't ask me how I know ;-)

      There are a couple of tabs that show the amplitude and phase charts in
      addition to the controls, and a clear all button if you want to start
      again.

      CW TX

      Assuming some cal work has been done and you have wired up the serial
      port as described earlier on, simply plug in the keyer or hand key and
      off you go. There is no need to select TX, the software flips between
      the two automatically.

      There are a few rough edges, like the RX monitors the TX and not
      everyone will like that. Also, the AGC gets pumped by the TX - this
      can be fixed by temporarily suspending AGC while the transmitter is
      on. I'll spend a week or two getting CW straight, and then do
      something with the SSB side.

      Have fun & 73,

      Duncan
      M0KGK
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