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| Joined: | Dec 12th, 2007 |
| Location: | Dunedin, Florida USA |
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I'been testing the germanium diode to better understand the transition from non-conduction to the conduction zone and the result is not what I expected. I found that test signals (sine wave tones from a frequency generator) get thru the diode even at amplitudes of 1-2 mV. My previous understanding would have predicted that a minimum signal level of 0.25 - 0.3 volts would be necessary.
Google searching came up with:
Diode Voltage/Current Curves: Does a Specific "Knee" Voltage really Exist?
at:
http://www.bentongue.com/xtalset/7diodeCv/7diodeCv.html
Graph (3) clearly (?) shows poistive current flow through the germanium diode at 0.0 volts. Graph (4) shows more detail. The slope of these current flow curves is still in the nonlinear (or less linear) region of current flow, but current is flowing.
My testing does not show the same thing for silicon diodes, tiny signals of a 1 - 2 mV don't get through, at all.
The Raudive design may be taking advantage of these tiny current flows within what is supposed to be the cutoff region of the forward bias voltage.
This cutoff region is something else I google searched and I found something interesting about it is the Scole Experiments. At:
http://www.thescoleexperiment.com/s_files_13.htm#fig_04
A spirit discusses the means of transmission of voice messages. He said:
" . . . (in a very simplified manner) the basic principles of the silicon chip, which uses a semi-conductor (silicon in this case but the theory is the same), and talked to us about something referred to as the 'cut-off point. This cut-off point is very interesting, especially in relation to our other experiments.
As this cut-off point is reached, and as I understand it, this can be due to temperature/pressure (remember the germanium is under a certain amount of pressure), the semi-conductor becomes unstable. This instability is then followed by the 'cut-off, or in other words, shuts down. It is, he explained, this instability or fluctuation in direction that provides a 'point of entry'. This reminded us of the fluctuations in the 'energy fields' that cause the 'void' to be formed in the receptor. Perhaps there are 'doorways' involved here, . . ."
This same spirit also stated:
. . . that electromagnetic waves (which include radio waves) are not involved in the reception of these communications. He told us all, not to fall into that trap as they are purely spiritual vibrations or waves that will be using the germanium as a point of entry or focus.
(Note: I suggest reading the whole page for more insight and to see their communicator design)
If the "cutoff" he is describing is the "non-conduction zone" of the germanium diode it might suggest that the best bias voltage is one that brings the diode into its leasst stable conduction region. Not sure what forward voltage that would be. Could be 0.0V, the place in the curve where current flow changes from positive to negative. Could be where current flow is least linear, from Graph (4) that looks like about (-)0.05 V with a current flow of about (-)0.75 uA.
About the coil . . .
It looks like it is being used with the diode to form a high pass filter. Its impedance is a function signal frequency. This impedance is so low at frequencies below about 100kHz that, that part of the antenna signal passes through the coil to ground, never passing thru the diode. As the signal frequency increases the impedance also increases sending more of those frequencies through the diode. The higher the signal frequency the more of the signal goes through the diode.
Maybe that has something to do with what is meant by:
"According to Raudive’s colleagues, the second unit helps you pick up ”higher-frequency voices,”
As referred to in the article in the October 1995 issue of Popular Electronics at:
http://www.itcbridge.com/forum/view_topic.php?id=1402&forum_id=5&page=2
Still working at understanding how this works . . .
Bruce