[ARC5] Pre-WWII product detector

[Bill Fuqua]

   Somewhere I heard a statement that the first product detectors were not 
developed until after WWII.
However, there was an interesting one used long before WWII.  It was the 
Marconi Balanced Crystal
Detector.  It  used two biased detectors connected in such a way that their 
detected signals would
cancel out. However, there is another RF tank circuit driven by a buzzer 
that provides the BFO signal.
The following has a schematic of the detector.
http://californiahistoricalradio.com/CHRSPix/10LeeDunwoodyCoal2009.pdf

Here is a description of it, however in this drawing one diode is reversed.

<http://books.google.com/books?id=Myt_AAAAMAAJ&pg=PA238&lpg=PA238&dq=marconi+balanced+detector+Undamped&source=bl&ots=xKFIq6YSc4&sig=AgyS65nR2cXSHkK3902IzyszmZU&hl=en&sa=X&ei=2-_4T4DkAYG29QT3goWJBw&ved=0CE4Q6AEwAA#v=onepage&q=marconi%20balanced%20detector%20Undamped&f=false>

This is indeed a product detector an behaves as one. With out the BFO 
signals cancel out but adding the buzzer and  the tank circuit the diodes
are driven out of balance by a damped wave and beat with the incoming 
signal. This also increases the apparent  gain, or reduced the loss, of the 
detector
by around 2 orders of magnitudes.


73
Bill wa4lav