[RTTY] UPDATE Re: FSK Keying

[Joe Subich, W4TV]

On 2/26/2018 3:11 PM, David G3YYD via RTTY wrote:

> I looked at programming a PC connected UART, but all the 
> specifications I looked at for current stock are incapable of doing 
> 45.45 they do 45 if they can go that slow.

The way to get a PC connected UART to do 45.45 baud is to *hack* the
standard serial driver to rewrite 45 baud to 45.45 baud (change the
baud rate divisor for 45 baud to 45.45 baud - decrease the value of
the baud rate divisor by 1%).  That was a whole lot easier in the days
of MSDOS and Windows 3.1/95/etc. but should still be doable with the
proper software tools.

I believe one of the older USB (1.0) to serial bridge chips even
provided a way for the product maker to do so by customizing the
drivers (it was called "aliasing" - any standard baud rate could be
rewritten to any custom baud rate within the 230 kbps maximum data
rate limit).

73,

    ... Joe, W4TV


On 2/26/2018 3:11 PM, David G3YYD via RTTY wrote:
> Joe and Ed
> 
> Yep TinyFSK does an excellent job, which is why I made a bespoke driver
> within 2Tone for it. In testing TinyFSk I found no detectable timing jitter.
> I looked at programming a PC connected UART, but all the specifications I
> looked at for current stock are incapable of doing 45.45 they do 45 if they
> can go that slow.
> 
> Still does not avoid the wide radio FSK problem. Nor as pointed out wideband
> TX noise/oscillator phase noise. The later of course is with us whatever the
> mode used.
> 
> The K3 is, as far as I know, the only radio that filters its FSK signal so
> it has a reasonable FSK bandwidth. There may be another but I do not know of
> one.
> 
> The K3 driven by a sound card is the set up I use for SO2R contesting. I
> tried to overdrive a K3 by setting all the gains in the PC and the K3 to the
> maximum. I then looked at the K3 TX spectrum using the other K3. I could not
> see detect any spurious due to overdrive at all.
> 
> The K3 line in was connected direct to the sound card line out with no
> transformer or attenuation. Conclusion I came to is the K3 is very well
> engineered in this area (as it is in many other areas of performance) and to
> have no worries about overdriving it with audio.
> 
> Note the very cheap $5 USB sound cards are not very good so better to use
> $25 ones. More expensive ones are just as good but you pay more $ than
> needed.
> 
> 73 David G3YYD
> 
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