[RTTY] Article by Brian Beezley, K6STI

[ON7UI/Etienne]

> Does someone know what the baud rate of RTTY 23 is?  I think
> most people are saying that the shift is 23 Hz.
>
> I would not classify what we use on 45 baud Baudot RTTY to
> be narrow shift.  It has a ratio of shift to baud rate of
> 3.7 or thereabouts.
>
> However, if RTTY 23 is operating at 45 baud, then, indeed,
> it is narrow shift with the shift to baud rate ratio of
> 0.5.
This could be the clue. As far as I know it is 45.45 bauds.
this makes the deviation 11.5 Hz and the modulating frequency 22.8 Hz
(45.45/2).
By Fourier this square wave , considering it to be a square wave composed of
an infinitif number of sine waves (fundamental 22.8 and all harmonics) a
theoretical reasonable facsimile siignal of the wave is reconstructed up to
the 5th harmonic. A very usuable wave results if only the 3th harmonic is
used. This leads to the conclusion that only the 3th
harmonic or 68.4 Hz must be transmitted.Bessel's functions determine an
appreciable
sideband up to the 7th order or 478.8 Hz.
the bandwith needed would be 23/68.4 or 0.336.
Using Terman's approximitation (*) minimum bandwith = 2(23+68.4)= 182.8 Hz
Decreasing the baudrate would decrease the bandwith.
* F.E. Terman ,Radio Engineering, 3rd ed, Mcgraw-Hill. p486.

ON7UI/Etienne