[GreenKeys] Torn tape continuous transmissions

[Harold Hallikainen]

On Fri, July 24, 2026 4:11 am, Nick England wrote:
> The messages were sequentially numbered on each outgoing channel. The
> header contained station and channel ID characters plus the message
> number. The receiving station checked the numbers to detect missing or
> garbled messages and request retransmission if needed. This was
> particularly valuable for RTTY channels.

That's great! I see this as the predecessor to the internet's Transmission
Control Protocol where there are sequence numbers to detect missing
packets and put stuff back in order in case it arrives out of order. How
could they tell if there was an error in the message?

With the DSP TU ( https://w6iwi.org/rtty/DspTU3/ ) you can type !ER on the
KSR to get an error report. This prints a count of the total characters
received and the number of characters with bad stop bits and the ratio
between the two. While not a perfect measure of errors, a bad stop bit
definitely indicates an error.

I'm also looking at how different demodulators handle an impaired signal.
At
https://w6iwi.org/rtty/audio/#:~:text=spiceaudio220629_2022.wav-,30%20lines%20of%20RY,-%2C%2035%20of%20each
, I have links to audio from KFS where I transmitted 30 lines of RY at
both 170 Hz shift and 850 Hz shift. The DSP TU has an RyCount command in
the command interpreter that outputs the number of Rs received and the
number of Ys received. Since an error will most likely result in a
character other than R or Y, this seems to be a reasonable measure of
demodulator performatnce with an impaired signal. It would be great if
people could run this audio through their terminal units and get a count
of Rs and Ys. Instead of counting the characters by hand, a loop interface
to a computer along with Baudot to ASCII conversion followed by a program
to count the Rs and Ys would be easier and more accurate. On the DSP TU, I
want to try different settings on tone filter bandwidth, limiter vs no
limiter, dynamic threhshold control, etc.

By the way, the incomplete manual on the DSP TU is at
https://docs.google.com/document/d/1npJU1f_ZlEMmIXo5jZ4FI-q50hffB5Tv5nvFCtLdV70/edit?usp=sharing
.

Harold
https://w6iwi.org




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