[Boatanchors] Fwd: 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