[RTTY] Mark & Space - High Tones

[Kok Chen]

>From the introduction to Section 16.2.1 (RTTY) of Chapter 16 in the 2010 and 2011 ARRL Handbook for Radio Communications:

"RTTY consists of a frequency shift keyed signal that is modulated between two carrier frequencies called the mark frequency and the space frequency.  The protocol for amateur RTTY calls for the mark carrier frequency to be the higher of the two in the RF spectrum."

Then, under "FSK vs AFSK Modulation":

"AFSK can be generated by using either an upper sideband transmitter or a lower sideband transmitter. With a USB transmitter, the mark tone must be the higher of the two audio tones in the Audio FSK signal.  The USB modulator will then place the corresponding mark carrier at the higher of the two FSK carrier frequencies.  When LSB transmission is used, the mark tone must be the lower of the two audio tones in the Audio FSK signal.  The LSB modulator will then place the corresponding mark carrier at the higher of the two FSK carrier frequencies."

Under "'Spotting' An RTTY Signal,"

"By convention, RTTY signals are identified by the frequency of the mark carrier on the RF spectrum.  "Spotting" the suppressed carrier frequency dial of an SSB receiver is useless for someone else unless they also know whether the spotter is using upper and lower sideband and tone pair the spotter's demodulator is using."

When Ward N0AX asked me to contribute to the 2010 and 2011 Handbooks, I had very carefully included those paragraphs just because these topics keep getting asked on this reflector every year or so.

(Of course cocoaModem has a menu to select between USB or LSB for RTTY, PSK31, MFSK16, ASCII RTTY, DominoEX and SITOR-B.  I was surprised to see so many software modems in Joe's list that don't do it, since it really doesn't take more than a few minutes of mostly clerical work.)

73
Chen, W7AY