[RTTY] (no subject)

[Kok Chen]

On Mar 13, 2008, at 3/13    9:25 AM, Gedking at 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