[RTTY] RTTY Cut Numbers

[Kok Chen]

On Jan 10, 2016, at 11:28 AM, G3YYD wrote:

> If the checksum character is in error?

Send "AGN?" of course :-).   

You can even automate the "AGN?", but with poor propagation, the back and forth could end up sounding like Packet Radio :-).

Sending the serial number twice is a form error detection, that is why we use it today, but it is rather inefficient.   And the response to an error is similarly, either "I don't need that mult," or sending "AGN?"

Sending the exchange 3 times allow a single error to be corrected, but, like repeating something twice, is also inefficient.  Even the rudimentary Hamming code is better for correcting single errors.

The "3 copies" methodology has even been used in hardware in spacecrafts.  Avizienis at JPL called it "Triple Modular Redundancy."  Nowadays, in the same vein as error correction codes like the Hamming code (the grand pappy of them all), Arithmetic Codes are much more efficient hardware implementation than triple modular redundancy.

Happy New Year 2016, David!

Chen, W7AY