[RTTY] TinyFSK modem for 45 and 75 baud

[aflowers at frontiernet.net]

Bill asked:

>What does this do that MMTTY and a pair of one-transistor drivers for FSK
and PTT does not do?

Hi Bill,
 
Here's a concrete example if it will help.  I have a note here from Jun 7 of this year that I observed W6WRT with a stop bit length consistently at 37ms.  I think this was during some DL contest or something.  Were you aware that you were (perhaps still are?) sending RTTY with around 1.7 stop bits?  So, if this was the UART arrangement you spoke about in this thread, you probably already are being affected.  Just because you have a UART clocking the bits to the radio doesn't mean that software upstream isn't going to affect timing.  If MMTTY is pushing characters to the UART at less than the outgoing data rate you will get stretched stop bits.  This arrangement does put you at the mercy of the software developer.

To be clear, this isn't some domestic spying program--you just happen to be loud in NY on 20m with little in the way of path distortion in the late afternoons :-)  I'm quite sure I could find hundreds of examples of strange timing in a big contest, including many with variable stop bit lengths.  2Tone is a tool that can help you see what you are really sending.  It might be worth people having a closer look, rather than just assuming.  

So Bill, back in your particular case... if you were to use TinyFSK, you will get 1.5 stop bits, consistently no matter what your PC is doing.  Chen's comments regarding SNR not withstanding, you would additionally get back 4ms per character transmitted, if that matters to you. 

Andy K0SM/2