DUH!

You have to do full-wave rectification if you are going to use a
avaraging type of filter. Think about it.
The precision half-wave circuit that responds to peak should work well
also. I'll probably stick em both on the board.

73
NEO

N9NEO wrote:
wrote:
N9NEO wrote:
There looks like a typo in schematic.

http://www.amwindow.org/tech/htm/alowdisdet.htm

Amplifier inputs have to be swapped at the two rectifiers.

later
NEO

I don't remember any errors, but it has been 8 months since I built one
of these. I will open up my outboard detector and verify the design. It
will
have to wait until Sunday night at the earliest.

Terry

No big deal there Terry, it's really a minor issue and probably would
work no problem anyway. What I found is just that the way the detector
is shown the output will be negative. I simulated it in
SwitchercadIII. (That's my secret to designing pc boards that work
without breadboarding.) I would appreciate if you look at and comment
on a couple of things with the circuit though. I am a power supply guy
and I don't know too much about detectors.

Rob uses a RC filter on the output of this thing so that the output is
an avaraging operation rather than responding to the peak of the
waveform. It looks like the pole is set for near 5kHz so some phase
distortion is going to be introduced - probably not a big deal. Rob
goes out of his way to do a full wave rectification, but that doesn't
make much sense to me with the filter he sticks on the end.
What do you think about just doing a detector that responds to the peak
of the waveform in a half-wave type rectifier? By the time this signal
goes through a 4kHz elliptic filter there isn't going to be a microvolt
of 455kHz signal to be found. Gain the IF signal up so that any error
due to diode matching will be minimized. I have a circuit that uses 3
schottkys in Spice that should do a nice job. I can send it to you if
you run Switchercad. It's a free download.

regards,
Bob