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Re: [linuxham] fldigi 0.956 beta posted

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  • Rick Kunath
    ... Because the LSB modulation process inverts any tone frequency sequence. So if you are right-side-up on everything on USB, going to LSB inverts
    Message 1 of 5 , Sep 23, 2006
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      W2AGN wrote:

      > Now I'M confused. How can both USB and LSB REV OFF both be correct
      > signal inversion?

      Because the LSB modulation process inverts any tone frequency sequence.

      So if you are "right-side-up" on everything on USB, going to LSB inverts
      everything, and reversing everything automatically makes it
      "right-side-up" again.

      Look at it this way...

      On RTTY, the FSK standard is to always have the Mark tone the higher RF
      frequency of the Mark/Space tone pair.

      Using AFSK on USB, you would apply the tone pair such that the Mark
      audio tone is the higher audio frequency. Because of the modulation,
      this would make it farther from the carrier re-insertion frequency, and
      place it at a higher RF frequency than the Space audio or RF tone.

      In LSB this is opposite. Having the Mark audio tone the higher audio
      frequency also moves it farther from the carrier re-insertion frequency,
      just like USB, but now this is in the opposite frequency direction, i.e.
      farther *down* from the carrier re-insertion frequency, and the Space is
      higher in actual RF frequency. The RF position of the Mark and Space
      tones is reversed even though the actual audio tones follow the Mark
      higher standard. So, when you transmit, you're upside down.

      Just reverse everything (the audio) on LSB and you are back to normal.
      Then using the reverse button on the main screen works as you'd expect,
      actually reverses everything.

      Make sense?

      As to actual FSK, that depends on how the particular rig is designed.
      One can but hope that the radio's designers understood that Mark shifts
      the carrier upwards. The only issue you have then is in any interfacing,
      so that the FSK keying output is correct, which fldigi does not support yet.

      The only relevant suggestions I might make to Dave would be to add a
      RTTY "sweet spot" entry, so that you could set it to your rig's RTTY
      narrow filter position. That way, when you hit QSY, you'd move the
      signal to the center of the RTTY filter passband, usually set to
      high-tones (I think).

      The only other thing I can think of is some way to tell fldigi for
      non-CAT rigs, whether you are using LSB or USB in the interface setup
      tab. But really, as long as *you* know and know to enable reverse on
      LSB, it's likely unnecessary. Simply use USB for everything.

      So as a question to those with CAT rigs... when you go to RTTY mode on
      the rig's mode switch, what does hamlib report back to fldigi? Will
      fldigi know whether RTTY is USB or LSB on that particular rig and adjust
      accordingly?

      Rick Kunath, k9ao
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