wrote:

Almost all AM detectors use Germanium diodes.
This link shows an interesting alternative:
http://www.wsdmag.com/Articles/Print.cfm?ArticleID=8628
Ge diodes have a typical Vf (forward conduction volage)
of .4V.
"Silicon Schottky diodes are commercially available
in four different versions. They offer forward
voltages of approximately 600 mV for high barrier,
330 mV for medium barrier, 280 mV for low barrier,
and 180 mV for zero-bias detectors.".

I am going to try and drive the detector diode in
my R2000 with a ~20K resistor feeding the junction
of to force the Ge diode slightly into conduction.
(for a diagram of the R2000 please see:
http://www.qsl.net/kc7bum/schematic-1.jpg
for a diagram of the R2000)

But I would prefer to find a diode with the lowest
Vf possible. Back in the mid 1970's GE had a diode
with a very low Vf, but I can't remember the name.

Does anyone know of a source of Shotkey "zero-bias
detector diodes"? And will diodes from a microwave
detector work in at 455KHz? I have several microwave
detector diodes that I would sacrfice in a minute if
there was a good chance they would work.

This weekend I intend to go to a friend to whom I have
loaned my ancient R392 which has a 455KHz IF out port,
and see how it works.

I'm not an expert on this by any means but as I rcall we went through the
Schottky diode craze about 20 years or so and for the most part it seemed to be
bunk.

Perhaps one of our resident techs might weigh in on this.

dxAce
Michigan
USA

dxAce wrote:

I'm not an expert on this by any means but as I rcall we went
through the Schottky diode craze about 20 years or so and
for the most part it seemed to be bunk.

Perhaps one of our resident techs might weigh in on this.

dxAce
Michigan
USA
---------------------------
I am hoping to improve the AM detecton in the R2000. I have done some
experimenting and decided that changing the caps was worthwhile. I
tapped straight off the detector with a DC coupled hi-Z FET, fed it
to my classs A servo heaphone amplifier and switched back and forth
between the my buffer and the Rec out, and then the input to the power
amp IC. This porved somehting I already knew, but IC audio amps
suck. Lots of crossover distortion. By taking my audio upstream
I was able to understand weak singals. As opposed to just telling
something was there. I using my HiFer beacon feeding a attenuator
and using my MC power divider to feed my antenna and the RF
to the R2000s. This allowed me to nearly duplicate real world
conditions with QRN/M. I used a local 24 hour talk radio station,
for my modulation source. Pulled it from my DX398 tape out.

I am going to be very busy changing caps for the next month.

I have decided that some of the low level "Grunge" that I
wrote off to PLL phase noise is in fact distortion caused by the
caps, and the nasty cross over distorion in the audio power IC.
I am going to replace that stage with a much better design.

While I would love to buy a new, or better used receiver, I have
to stay within a budget, so it is either modify or accept.

Of course some people mihgt nominate me for "sows ear
to silk purse" prize of the year.

Later tonight I am going to try adding some forward bias
to the AM detector diode. Distortion is after all another form
of noise.

Terry
Terry

Terry - let us know how forward biasing the AM detector diode works
out. Hopefully it will reduce distortion.

Frank