General: 2m RTTY/Data Symbol Rate

General: 2m RTTY/Data Symbol Rate

What is the maximum symbol rate permitted for RTTY or data emission transmissions on the 2 meter band?


A. 56 kilobaud

B. 19.6 kilobaud

C. 1200 baud

D. 300 baud

The answer is B. 19.6 kilobaud.  But why?  It has to do with the amount of bandwidth used by a signal.  1200 and 300 baud take up a very small amount of bandwidth, which is useful on the HF bands, but not so much on 2m.  You can still use these rates on 2m, but it isn’t required.  56kbaud would require too much bandwidth on 2m.

The reason for this goes all the way down to the wavelength of the signal.  In order to pack more symbols into a given space of bandwidth, you need smaller wavelengths.  HF wavelengths are relatively long, so you either need a larger bandwidth, or a slower rate to transmit the same number of symbols.  At higher frequencies, the wavelength shrinks, so you can fit more variance, and therefore more symbols, in a given passband.

Refer to 97.305(c) and 97.307(f)(5) for more information.


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