[GreenKeys] N3CRK stream stop bit length

[Harold Hallikainen]

I see an error in the notes on the N3CRK logic analyzer trace. It says 44
ms is ideal, but should be 22 ms. The 44 ideal is from the previous logic
analyzer trace where the start bit and D0 were both space.

Oops!

Harold
https://w6iwi.org


On Fri, August 11, 2023 5:55 pm, Harold Hallikainen via GreenKeys wrote:
> I've been working on my DSP TU ( https://w6iwi.org/rtty/DspTU2/ ) and
> testing with various internet streams. It is interesting that I get an
> occasional error on the N3CRK 850 shift stream (all streams at
> https://w6iwi.org/rtty/audio/ ).
>
> Attached is a logic analyzer capture of RY sent by KE3BK and demodulated
> by my TU (RttyRYTiming.jpg). This prints error free on my model 15. In
> particular, note the short gap between characters on the top trace. This
> is the 31 ms stop bit.
>
> Also attached is the N3CRK 850 Hz stream (RttyN3crkTiming.jpg) from
> http://n3crk.ddns.net:8000/850 . It is interesting to note that the
> characters are sent in pairs with a 22 ms stop bit on the characters that
> are run together.
>
> I noticed the issue on the 850 Hz stream, but looking at the 170 Hz
> stream, it looks the same (character pairs with 22 ms stop bit).
>
> I believe it is standard to use 22 ms start and data bits with a 31 ms
> stop bit. But, should a 22 ms stop bit work on a model 15? It SEEMS like
> we'd have the following timing:
>
> Start bit mark to space transition: 0 ms
> Sample D0: 33 ms
> Sample D1: 55 ms
> Sample D2: 77 ms
> Sample D3: 99 ms
> Sample D4: 121 ms
> Sample stop bit and stop: 143 ms (22 ms after middle of D4)
>
> With a 22 ms stop bit, there would be 11 ms from the middle of the stop
> bit to the beginning of the start bit.
>
> With a 31 ms stop bit, there would be 20 ms from the stop bit sample (22
> ms after the middle of D4) to the beginning of the start bit of the next
> character.
>
> It makes sense to me that the model 15 would sense the stop bit 22 ms
> after sensing D4, but does it sense it later, causing a problem with a 22
> ms stop bit?
>
> THANKS!
>
> Harold
> https://w6iwi.org
>
>
>
>
>
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