Solid State Precision Detector

[N4LTA]

I have recently build three precision AM detectors and am a bit puzzled at my test results.

The first one used three MPF 102s and was found on a Google search. It was designed to be a low distortion detector.

The second one is found on the AM Window tech window and uses three LM318 Op Amps.

The last one is the detector described by W1QEX and is made to work with a tube type rig and uses the LM318 and has an AGC system.

My test methode was using an HP signal generator set at 455 Khz modulated with a single tone 1 khz sine wave.

I tested the first two detectors at approximately 1 volt in to the detectors and got a pretty severely distorted outputs on both detectors. I was expecting to get a near perfect 1 kHZ sine wave. Varying  the modulation percentage changed the distortion but it was severe at nearly all levels. I also varied the input voltage levels with no real change  - the distortion changed but it was severe.

Am I missing something here? The modulated 455 Khz waveforms looks near perfect on the scope.

I have not tested Steve's detector but will do so soon as I need to get the more complicated power supply requirement set up in the shop.

Pat
N4LTA

[N2DTS]

I test built one of those, forget which, and had the same results.

Why use ic chips/solid state stuff?

The low distortion tube circuit I found works the bomb, and has VERY low distortion.
Under 1% I think the specs were....

I still think the homebrew receivers sound and work better then the flex 5000a, which seems to have the best modern receiver I ever tried.

Brett

 

[N4LTA]

Why?

Because  most tube detectors used in communication receivers are awful. They perform well with strong signals and very poorly with weak ones.

I am not trying to get into a fight about which is better - I am experimenting to find out myself. There is no reason that a precision diode made with a quality quality high speed op/amp with high speed diodes diodes should not outperform a tube diode detector.

Steve's detector seem to show some promise in my initial tests. Has anyone else built one?

[N2DTS]

The experimentation/trying things is the fun part, I agree with that!

The circuit I found seems to do well with strong and weak signals, it seems a bit better than the flex with really weak signals.

It might not handle 200% modulation well, I have not compaired that with the flex.

Brett