Great, thanks, Joe.
I'm building a tone converter (AFSK tones to FSK codes) to support WSJT modes
on my direct synthesis millimeter wave Tx (no up converter, so no SSB; AFSK not
possible).
It appears that the Gaussian filtering makes it harder to quickly and precisely
identify tone changes with out introducing symbol timing jitter. I'm finding
that most GMSK modes can be tone converted if the pitch change detector is
carefully tuned, but some still have to choose between pitch accuracy and
symbol jitter. GMSK helps cut the sidelobes/keying splatter, but does
introduce some ISI and slight sensitivity reduction.
On the other hand, unshaped keying is easy to tone convert accurately. Glad to
hear that the microwave modes are continuing to use unshaped keying.
73,
Mike
> On 02/22/2021 11:51 AM Joe Taylor <[email protected]> wrote:
>
>
> On 2/22/2021 2:41 PM, MIKE LAVELLE wrote:
> > I read that FT4, FT8, FST4, FST4W use Gaussian FSK.
> > Is it correct that all the other modes use unshaped keying?
> > Specifically, does Q65 use gaussian or unshaped keying?
> > Thanks,
> > Mike K6ML
>
> Q65 uses continuous phase frequency-shift keying (CPFSK) without shaping
> at the frequency transitions.
>
> The advantage of shaping the frequency transitions of an M-FSK signal
> decreases rapidly when M is large, as in the M=65 case for Q65.
>
> -- 73, Joe, K1JT
>
>
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