Re: [linuxham] fldigi 0.956 beta posted
- W2AGN wrote:
> Now I'M confused. How can both USB and LSB REV OFF both be correctBecause the LSB modulation process inverts any tone frequency sequence.
> signal inversion?
So if you are "right-side-up" on everything on USB, going to LSB inverts
everything, and reversing everything automatically makes it
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.
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
Rick Kunath, k9ao