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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
