[RTTY] uh, what about spectrum?

[Kok Chen]

On Jan 16, 2006, at 12:03 PM, Michael Keane K1MK wrote:

> the bandwidth that contains 99% of the energy i.e, the bandwidth  
> such that, below its lower and above its upper frequency limits,  
> the mean powers radiated are each equal to 0.5 percent of the total  
> mean power radiated by a given emission.

>>> Section 2.202 of the FCC rules specifies that the
>>> necessary bandwidth of an FSK signal is equal to
>>> 1.2 x Shift + BaudRate.

The problem is that the latter definition does not necessarily mean  
that the 1% power is maintained.  A poor keying waveshape in an FSK  
transmitter can lead to a much wider (as defined by 1% power) signal  
than specified under Section 2.202.

If the new bandwidth rules will still allow the use of the (2.202)  
formula and allowing us to ignore the 1% formula, then we can comply  
(by letter of the rule) by using 45.45 baud (so mechanical teletypes  
can still copy) and up to a 128.8 Hz shift.

If we call it 115 to 125 Hz shift, that will allow some slack in baud  
rate inaccuracy (how precise are bit timings from mechanical  
teletypes, anyone?) and also shift inaccuracies (FSK on rigs like the  
Omni V and VI can drift over temperature and time).

Now, this does not mean that we are complying by the spirit of the  
rules (as W6WRT mentioned, perhaps the new rules are being written  
with the hope of giving CW ops some RTTY-free spectrum).

> Below 10m: symbol rate <= 300 bauds; shift <= 1 kHz.

Hope the "free software" guys don't complain if they can't copy me  
while I am testing with odd baud rates and shifts :-) :-)

73
Chen, W7AY