[RTTY] K or carriage return

[Kok Chen]

On Feb 14, 2011, at 2:48 PM, Jim Reisert AD1C wrote:

> Incidentally, this is why the space shuttle and other mission-critical systems have voting logic with at least three voters.  This is my
> attempt to model this.

Triple Modular Redundancy (TMR) hardware was already in use back in 1969 by Avizienis at JPL in spacecrafts when I first studied papers about it.  It had most certainly been used earlier than that.

The nice thing about TMR is that you don't need specialized hardware; you just build three times the amount of hardware and a simple voting circuit.  Later work on codes for correcting arithmetic errors were more efficient; papers on "fault tolerant computing" were in vogue in the 1970s.  They were able to correct CPU errors with some tens of percent extra hardware instead of three times the amount of hardware.

The same is true with data.  Except that in the case of data, good error correcting codes had existed for a much longer time.  Systematic codes for correcting data transmission errors were introduced by Hamming in 1950.  

In addition to error correcting codes, encoders used for modern HF modes often include an interleaver to "spread the data out" so that consecutive bits don't get smashed by deep QSB.  Many DXpeditions already try to do something similar to counter QSB by transmitting "AD1C 599 AD1C," which is obviously much better in the presence of QSB than transmitting "AD1C AD1C 599."  

Even Amtor (a.k.a. SITOR-B) repeats characters with a large time gap in between the two copies.  Back when W1AW transmitted Amtor bulletins right after their RTTY bulletins, Amtor could provide perfect copy when the RTTY copy had already turn into gibberish.

Even better than repeating would be to encode the callsign and an RST into something like 4DF1GXZ8QP for transmission over the air, and let the decoder expand that back to a pristine "AD1C 599."

Just because one uses RTTY already means that one is already accepting gross inefficiencies (both in bandwidth and in transmission time).  Baudot RTTY is fun, but you can never accuse it of being efficient :-) :-).  

73
Chen, W7AY