[ARC5] Pre-WWII product detector

[Richard Knoppow]

----- Original Message ----- 
From: "Bill Fuqua" <wlfuqu00 at uky.edu>
To: <arc5 at mailman.qth.net>
Sent: Saturday, July 07, 2012 7:40 PM
Subject: [ARC5] Pre-WWII product detector


>   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

     Thank you very much for this fascinating discussion and 
the references.  I think I have Butcher's book but he wrote 
several.
     I did a somewhat casual patent search for H.I.Rounds 
but could not find anything via Google Patents. It seems 
unlikely the circuit was not patented by him or by Marconi. 
Google does not always find patents reliably.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com