[GreenKeys] Error-correcting codes

[valerie zeiser]

In 1973 I worked for a small gov't defense plant in
Freeport, New York.

We were building MDTs (Mobile Data Terminals) that were
10' cubes, full of data communications equipment, that
were field dropped along with matching-sized power
generator and radio station.

I ran a mock-up, which was a big test bench copy of
the MDT. Here I tested out each piece of equipment
before it went into the MDT that was under construction.

Some of the testing was chimpanzee work: I didn't know
what I was doing - I just followed the procedures in
the test manual - hey: I was only 19 at the time.

One day when I was testing the Codex DEC, I asked
the Design Engineer what the thing does. He smirked
and said "it does Data Error Correction". I knew
just as little now as I did before I asked. I said
"so, WTF does THAT mean?" :-)

He knew I was a ham, and that I played with RTTY.

He said "put the mock-up into loopback mode and send
a test message to the model 37-ASR". So I put in
the loopback plug and ran the test.

Then he said "what'll you think will happen if I
yank the loopback plug out?" I gave him a look like
"what are you - some kind of an idiot?:" and said
the data's going to stop.

He smirked, leaned over and yanked the plug.

The Teletype kept printing - PERFECTLY!

He waited a few more seconds and then leaned over
and plugged it back in.

I was like a deer caught in the headlights.

I took ALOT of mind-expanding drugs in the '60s and had
some weird things happen, but none of that rivaled what
I had just seen.   :-)

He went to the library, took out the Tech manual, and went
over the block diagram with me.

Needless to say, that was the office joke-of-the-week

73,
W6ESE - tonyp
NNNNZCZC

Dave Emery wrote:
> On Thu, Mar 10, 2005 at 09:17:25AM -0500, Tim McNerney wrote:
> 
>>When is the earliest anyone here can remember of error-correcting 
>>equipment being used in RTTY communications?
> 
> 	I worked for Codex Corp in the summer of 1966 when I was a
> senior in high school and at that time they had introduced forward error
> correcting RTTY equipment using Massey convolutional coding at rate 1/2.
> I know it was employed on at least a few NASA and military/spook HF
> circuits at the time - typically using two channels on a VFT 16 channel
> fdm mux for two bitstreams - one parity and one data.   I forget whether
> the box was capable of combining parity and data bits into one stream,
> but I think so...
>