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

N9NEO wrote:
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

Rob K2CU design goal limited the loading on the diodes.
D800 goes to the non inverting, very hi z, D801 goes to
the non inverting input of U6A and the gain is 1 so the
non inverted, now low Z, output goes to the inverting
input of U6A where the 18K resistor might give too much
loading. I built a simple, U6A less, version but it had
fairly high distortion. It sounded much worse then a
single diode detector.

In my wife's R2000 I went with a 0.001uF for the output filter cap.
For most SW/HF signals the tansmitted BW will be 5KHz. To
tell the truth the change from 0.0033 to 0.001 didn't make much
audiable difference. I didn't bother to make any tests.

For 455KHz IFs U6A/B will need to be changed. The LMC660 is
just not up to that higher freq. They do work fine at 50KHz.

The other improved AM detector with a single OpAmp works, but
diodes must be very closely matched. A simple DVD diode Vforward
will not suffice!

Petes AD607 synch detector has to be the simplest way to get going.
There are other approaches that might fare better. The SAD in the
R8B is much better then the AD607 or the AO7030+. Better as in
will never growl, and doesn't fo nuts with a strong adjacent signal.

The AD607 OpAmp fitler I/Q combiner page that I refferenced is well
worth the study. If done correctly, it is possible to exclude or reject
everything except for the desired signal.

The Synch detector group has some very interesting PDFs from
older approaches that go into the mind numbing math. I never got
the filter to work properly. There are no obvious typos, and the
design looks sound. When I run out of other projects I intend to
revisit this one because IF it can be made to work, the rejection
would be very useful.

My psuedo/quasi/faux "MAP"/SE-3 had several detectors. For reasons
that escape me I decided to add FM with a crystal discriminator. Works
great the 3 times I used it. Twice for 10M FM, and once for a Pirate on
6.925.
The least usefull part of my oatboard detector.

Terry

I might have to put hi perf detector project on the back burner for a
few weeks. Seems as though I've been called up by my next employer
for a 90 day contract job. I think he wants to make sure that I'm
somewhat sane before he takes me on full time. I can't really blame
him - after all I do subscribe to rec.radio.shortwave.

I really didn't want to go back to work till like March or April. I
left my last job designing large inverters back in October. The place
was a real pressure cooker and I needed some time off to figure out
what is real and what is just a product of my own paranoia. Ya know,
time for the voices in my head to subside. But feeling good enoughtnow
and I don't have to report till January 7 I think. It's a dream job
working for a govt contractor so lots of really cool test gear around.

I'm thinking about goin over to the wrecking yard and picking up a 50
dollar car and heading south to Key Largo to do some snorklin for a few
days. Maybe I'll take the plates off the car when I leave and set it
afire on the beach and just stick out the thumb. Maybe stop by
Cuhulin's place on the way down with a box of dog biscuits and a six
pack of Old Milwaukee.

73
NEO



wrote:
N9NEO wrote:
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

Rob K2CU design goal limited the loading on the diodes.
D800 goes to the non inverting, very hi z, D801 goes to
the non inverting input of U6A and the gain is 1 so the
non inverted, now low Z, output goes to the inverting
input of U6A where the 18K resistor might give too much
loading. I built a simple, U6A less, version but it had
fairly high distortion. It sounded much worse then a
single diode detector.

In my wife's R2000 I went with a 0.001uF for the output filter cap.
For most SW/HF signals the tansmitted BW will be 5KHz. To
tell the truth the change from 0.0033 to 0.001 didn't make much
audiable difference. I didn't bother to make any tests.

For 455KHz IFs U6A/B will need to be changed. The LMC660 is
just not up to that higher freq. They do work fine at 50KHz.

The other improved AM detector with a single OpAmp works, but
diodes must be very closely matched. A simple DVD diode Vforward
will not suffice!

Petes AD607 synch detector has to be the simplest way to get going.
There are other approaches that might fare better. The SAD in the
R8B is much better then the AD607 or the AO7030+. Better as in
will never growl, and doesn't fo nuts with a strong adjacent signal.

The AD607 OpAmp fitler I/Q combiner page that I refferenced is well
worth the study. If done correctly, it is possible to exclude or reject
everything except for the desired signal.

The Synch detector group has some very interesting PDFs from
older approaches that go into the mind numbing math. I never got
the filter to work properly. There are no obvious typos, and the
design looks sound. When I run out of other projects I intend to
revisit this one because IF it can be made to work, the rejection
would be very useful.

My psuedo/quasi/faux "MAP"/SE-3 had several detectors. For reasons
that escape me I decided to add FM with a crystal discriminator. Works
great the 3 times I used it. Twice for 10M FM, and once for a Pirate on
6.925.
The least usefull part of my oatboard detector.

Terry