[GreenKeys] RATTS

[jhhaynes at earthlink.net]

I think we're mixing up a couple of concepts here.

What RTTY has traditionally been is that with HF FSK the lower transmitted
frequency is the space frequency.  With audio AFSK the lower audio tone is
the mark frequency.  This predates amateur SSB.

Nowadays very few of us have Real FSK transmitters that wiggle the
actual VFO frequency.  Even the modern transceivers with an FSK input
make FSK by putting internally-generated audio tones into the SSB 
generator.  If you do this and the lower audio tone is the mark frequency
then you need to use LSB to make the lower HF transmitted frequency be
the space tone.  But you can just as well use USB and have the audio tones
reversed, lower audio tone is space gives lower frequency is space when
using USB.  Most of the sound card modems, whatever mode they are running,
have reversing "switches" so you can make the audio tones go either way
and use either sideband on the transceiver.

Now the other thing that is going on is that if you are going to make a
sked or have a net on HF you need to tell people what operating frequency
you have in mind.  In the old days we talked about the actual HF carrier
frequency.  To be precise, hams usually specified the mark frequency,
with the space to be 170 or 850 Hz lower; the military liked to specify 
the center frequency halfway between mark and space.  With modern 
transceivers we don't usually talk about the actual frequency of the RF
coming out; instead we talk about the frequency of the suppressed carrier,
which is what the dial on the radio reads.  So in this case if the audio
tones are, say, 2125 mark and 2295 space then the transmitted frequency
on mark is 2.125 KHz above the dial reading for USB and 2.125 KHz below
for LSB.  So if the NCS says the frequency is 3615 USB he means the mark
frequency is 3617.125; if he says 3615 LSB it is 3612.875   That's
assuming your audio tone for mark is 2125 Hz - it might be something
quite different.  But if you set your dial to 3615 and the net is on
3617.125 you won't hear a thing if you turn the switch to LSB.

In these days of soundcard software with many different modes, lots of
guys seem to be opting to run USB all the time and punch the REV button
for the RTTY mode.

Then there's another whole debate about whether we should always use
LSB below 10 MHz and always use USB above - maybe some transceivers
default to that convention.  

-- 

jhhaynes at earthlink dot net