Pete KE9OA wrote:

Just a follow up on the MW receiver design...............I have completed
all of the RF stuff. The rest is up to the software folks at work.
MDS is .08uV, overload takes place at 50,000uV. The overload will be better
on the final product..........I will use a VCA ahead of the 1st mixer.
I still may try to figure out a way to use the TDA1572's on board
oscillator........I don't know yet. Maybe tomorrow at work.
I have completed the quasi-synchronous detector, requiring only one chip
(Philips SA637). Very similar sounding to the low distorion envelope
detector on the TDA1572, except for slightly better readability when signals
are at the system noise floor (.08uV), and no distortion occuring when there
is signal fading.
A couple of people have e-mailed me about this design, so I will reiterate.
The quasi-synchronous detector consists of a mixer and a high gain limiting
amplifier. The I.F. signal is split into two paths. One path is applied to
the RF port of the mixer, while the other path is applied to the input of
the high gain limiting amplifier.
The limiting amplifier amplitude variations from the I.F. signal, providing
a square wave at the intermediate frequency. The output of the limiting
amplifier is fed to the LO port of the mixer, and the demodulated audio is
taken from the I.F. output port of the mixer.

Pete

Have you measured the final audio output distortion w/wo the sync'
detector working, to get an idea of how well the sync' works during a
selective fade?


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