View single post by sparks
 Posted: Jul 8th, 2011 02:00 PM
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sparks



Joined: Jan 15th, 2008
Location: New Zealand
Posts: 77
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Hi Bruce, Mike,
I just read your posts, and thought Id add my thoughts.

From what Ive read and experimented with, the Raudive diode is essentially meant to be a noise generator to provide raw material for subsequent metamorphosis into EVP inside a recorder or amplifier. The antenna length is I believe, adjusted in length until broadcast stations start to be demodulated (the threshold of diode conduction curve), providing a distorted mush of sorts - this is the desired outcome. The reception of clear loud stations is not desired. In all designs, the inductor is not tuned, so allowing a broadband reception and demodulation.
The later Psychofon was essentially a Raudive diode with a 2 stage rf amp preceeding the diode...
http://www.worlditc.org/c_04_s_bridge_11.htm
I have built this design and it is very broadband in nature, receiving many stations at once, which is the aim I think, and provides a rich mush of audio that has good harmonic content. I have also built a shortwave version that works well too.
The idea to pre-bias the diode would enhance its sensitivity, but within the context of how the device has been traditionally used, this enhancement might not be needed.
The Goniometer was another diode device, but in a ring modulator configuration, so quite a departure from conventional receiver design. It also has literature suggesting it provides a background noise floor that is suitable for metamophosis into EVP.
regards,
JEFF