[ARC5] Pre-WWII product detector

[Bill Fuqua]

Not only is this a product detector it is a "balanced mixer" if used properly.
However, as a mixer  or as they would say in the early days, first detector,
would be of little use without the advantage of some sort of amplifier.
73
Bill wa4lav

At 09:22 PM 7/7/2012 -0700, Richard Knoppow wrote:

>----- 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