On Mar 13, 2008, at 3/13 9:25 AM, Gedking@aol.com wrote:
> TX5C running USB es reverse??? I got em on 14084 LSB no reverse. I
> thought
> RTTY LSB common practice.??
You can use either USB or LSB as long as you arrange to transmit so
that the Mark carrier is the higher of the two RF carriers of an RTTY
tone pair, and properly receive and decode an RTTY signal that was
sent with the Mark tone being the higher of the two RF carriers.
If you use LSB receive, the Mark carrier becomes the lower tone of
the tone pair at the AF output of the receiver. Many surplus modems
from the old days used the 2125/2295 tone pair with Mark assumed to
be the 2125 Hz (lower audio) tone. That is why it was more
convenient for someone back then to operate RTTY using LSB.
However, by choosing the demodulator tones correctly, you can receive
under either LSB or USB.
When you transmit using AFSK USB, just pick the 2295 Hz tone as the
Mark frequency and you are indistinguishable from someone using 2125
Hz on LSB. (You will need to account for where you are transmitting
differently, e.g., ehen you spot a signal on the PacketCluster, since
LSB transmits with modulation that is below the suppressed carrier
and USB transmits with modulation that is above the suppressed carrier.)
Don't fall for the bogus statement that "you have to use LSB" which I
see repeated often.
Just remember the Amateur RTTY standard simply as "Mark is the higher
of the two carriers in the RF spectrum." How you achieve that is up
to you.
73
Chen, W7AY
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