[Boatanchors] Fwd: Pre-WWII product detector

Bill Fuqua wlfuqu00 at uky.edu
Sat Jul 7 22:42:55 EDT 2012

>   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.
>Here is a description of it, however in this drawing one diode is reversed.
>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.
>Bill wa4lav

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