[GreenKeys] TU replacement

[Jim Haynes]

On Wed, 21 Aug 2019, Harold Hallikainen wrote:
> Not existing right now, but I plan on building a demodulator using an
> XR2211. I've used this in lots of projects over the years, including
> driving a model 15 in the early 1970s.
>
Well there's the Volpe demodulator that uses that principle.  I'm not
authoritative, but have the opinion that phase locked loop demodulators
are only good if you have good signals, perform poorly with FSK in
the presence of noise and interference.  Which of course is not a problem
with ITTY, but for on-the-air use you need something better.

Jim W6JVE