[RTTY] High Speed RTTY again

[Kok Chen]

On Jan 28, 2010, at 5:40 PM, Joe Subich, W4TV wrote:

> Yes, MMTTY supports it ... go to the "decode" tab, select 8 bit, 
> 2 stop bits and your choice or parity. as well as the baud rate. 


7 bit ASCII is the standard, Joe, not 8 bits (ref: FCC Part 97.309(a)).

Ignoring the problem whether other people can copy you or visa versa if you run 8 bit ASCII, unless that 8th bit is coded as a parity bit for the other 7 bits, I don't know if you will even run afoul of Part 97.309(b) by transmitting 8 bit ASCII.  There is an FCC provision (ref: 2006 ARRL Handbook) for the 7 bit + parity case.  But (also stated in the 2006 Handbook) parity is seldom used for ASCII FSK by amateurs.

> It's probably wise to find an optimized BPF on the "demodulator" 
> tab as well - particularly if you are using a higher data rate. 

Many programs compute something close to optimal FSK bandpass filter automatically based upon the baud rate and the shift.  The baud rate should also have automatically set the width of the boxcar filter that RTTY uses for the matched filter.

73
Chen, W7AY