[RTTY] Jitter

[Hank Garretson]

G3YYD said:

The TX bandwidth for 45.45 baud FSK is dependent on the radio rather than
> the system used for keying within reason. Obviously if the keyer is
> producing lots of short transients then it will widen the bandwidth unless
> the FSK is well filtered within the radio.
>

That is what I thought, but wanted expert confirmation. Thank you David and
Ed.


> As for timing jitter, why keep it when it can be avoided? This will save
> having to repeat an exchange when it would have been copied first time if
> the TX was jitter free.
>
l
My excuse is that even with a wire antenna at only 46-feet high I do pretty
well and get very few repeat requests. Plus I have a lot of more pressing
projects on my plate.

Another big factor is that my second-story shack is located directly under
my antenna. One 40-meter inverted-V leg end is only four feet from the
shack outside wall. Needless to say I have huge RF-in-the-shack issues. So,
addressing jitter by using AFSK is problematic. Every extra cable adds
another level of RFI susceptibility.

2Tone says my jitter is 54 ms.

W7AY says:

If the signal starts with a very good SNR (your neighbor's RTTY signal),
> then your peak-to-peak jitter can be 11 millisecond before you see
> degradation for a 45.45 baud RTTY signal.
>

Can the derogation be quantified for my 54 ms?

If you are using 75 baud, the peak-to-peak jitter of 6.5 milliseconds will
> cause errors.  This is why most people consider bit-banged FSK from a
> computer to be unusable for 75 baud RTTY.
>

Not unusable here. I work plenty of stations in the RSGB 75-baud contest.
Very few repeat requests.

In any case, I really should go to TinyFSK.

Diddle Exuberantly,

Hank, W6SX