[ARC5] Some information...

[Kenneth G. Gordon]

I thought I would bring to your attention some interesting information from the latest issue of 
Electric Radio Magazine, and some "historical" info from my own experiences.

In that issue of ER, Pat Griffin AA4PG's article covers the addition of a product detector to 
an Elmac PMR-7 receiver. He uses an MC-1496 quadrature detector chip as his external 
PD.

This can be added to almost any receiver without doing any easily-unreversible mods.

Here is the interesting quote from his article:

"The first improvement I noticed with the product detector was increased sensitivity. Using 
the method outlined by W8BTA on the Internet at www.youtube.com, the minimum 
discernible signal (MDS) was 21 dB lower with the product detector. That is about a 10-fold 
increase in sensitivity and made an enormous difference in performance." (!!!)

Some 50+ years ago, I modified the detector in my NIB BC-779 to a triode-product detector, 
using the 6N7 noise limiter tube, and I also found the apparent sensitivity, and 
much-reduced noise, to be hugely improved. 

That receiver, after that mod, became my very favorite receiver for RTTY and CW. The 
addition of the PD made it very, very quiet, and I could hear things I didn't even know were 
in there before the mod.

So, Mr. Griffin's results completely coroborate mine, and I am very pleased, since when I 
have mentioned my results in the past, those have been doubted by some.

I tend to disagree with him on one aspect of this though: that is, what he calls "increased 
sensitivity", I have always called "apparent sensitivity" since the real sensitivity of any 
receiver is set by the RF amp stage(s), the mixer, and the IF strip.

So, I have never really understood where the increase in "recovered signal" comes from. 
After all, any circuit-improvement like this cannot recover a signal which is not already there.

In any case, as I have insisted for many years, the proper addition of a good product 
detector to our old receivers makes a tremendous improvement in both apparent sensitivity 
and reduced noise.

Ken W7EKB