[Elecraft] {k3} PSK31 tuning

[Kok Chen]

On Aug 14, 2010, at 8/14    9:57 AM, Dennis KB7ST wrote:

> KB7ST: What is the advantage of choosing a MARK tone other than 2125?

Many RTTY ops don't like to listen to such a high pitched tone pair in  
their headphones.  If you are tuning by ear, it is also easier to  
figure out how far and which direction you are off tuned when you use  
a lower tone pair (Weber-Fechner law).

The real question should be what is the advantage of choosing the  
2125/2295 Hz tone pair?

In the bad old days, the harmonics of a poor 2 kHz AFSK tone pair are  
better suppressed because they fall outside of the SSB transmit filter  
passband.  This has not really been a problem with current radios if  
you use the output sound card properly -- using close to full scale of  
the output sound card, but never saturating either the sound card or  
the rig's analog audio stages.

> KB7ST: I assume the SPACE freq would be 170 Hz higher ...

The Mark tone (the "rest" tone (a.k.a. stop bit) if you are not  
sending diddles) is by RTTY convention the higher of the two carriers  
on the RF spectrum.

If you are using LSB, Mark therefore becomes the lower of the two  
tones in the audio spectrum.  If you are using USB, Mark remains the  
higher of the two tones in the audio spectrum.

The Mark carrier is also by convention the reference frequency to spot  
an RTTY signal.  This convention is often overlooked by RTTY newbies,  
who would spot less than useful information, often their rig's SSB  
suppressed carrier frequency - causing some spots to be 2 kHz off :-).

73
Chen, W7AY