Rap 'n Tap
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From: tom sheridan
Date: 2/13/03
Time: 5:24:12 PM
Remote Name: 66.54.1.38
BROKEN LINKS. FIX THEM!
From: Garry Nichols
Date: 3/30/99
Time: 9:11:26 PM
Remote Name: 209.4.228.202
Hi Larry and all, You probably know (but others may not) that xtal earphones can be used backwards as microphones. The piezoelectric effect works both ways; varying electric current thru a crystal produces motion and varying motion produces a varying electric current. The AM station was producing a constant circulating current in the tuning circuit(s) of the xtal set. My guess is that the signal transfer to the superhet was by inductive coupling of the field around the xtal set tuned circuits to the field of the antenna circuit in the superhet. I believe that this is a different phenomenon than "radiation" of an electro-magnetic wave from one antenna to another. (The difference between the two phenomenon may have a grey overlapping area that someone versed in engineering can only answer.) It would be interesting to try this experiment over again with the superhet outdoors and as far as possible from the xtal set, but yet near or under the outdoor antenna. If the signal is received, then start moving it away from the site, keeping the same orientation between xtal set and antenna, and doubling the distance with each trial (less might be a waste of time). I'm not really sure about how the circulating current is being modulated by the earphone because I haven't learned that much about the details of diode operation. Perhaps someone else can offer something in this area. I'm working at the limits of my knowledge with this answer!