On (01 Sep 96) Bruce LeGrande wrote to All...
 BL> A couple years ago I had occasion to purchase a FRoG-7 from a fellow,
 BL> and in his vehicle was a DF device that consisted of a small flat box
 BL> (chassis) measuring about 5-8 inches square and about an inch tall
 BL> with a circle of 10 (or so) red LEDs on the top and a couple
 BL> mini-toggles on the rear edge (for power,
 BL> attenuation, etc...). This unit was in turn connected via a cable to
 BL> another smaller box with what looked like large nails (same number as
 BL> on the other box) pointed up through the top of it, and a magnet for
 BL> mounting it on the roof. If anyone has more info (ie schematic) on
 BL> this, I'd like to give building one a shot.  Please, no internet
 BL> sources.
 BL> From what I can figure, the distance between the spikes, and the
 BL> measurement of frequency shift differential (largest change) is the
 BL> theory behind this, correct ?   This project might also be of help to
 BL> the fellow having problems with the jamming SWL'er on his local
 BL> repeater, that I just read about here in the echo. ;)
What you saw is a commercially made/sold DFing device that measures the
received signal doppler shift difference between the various antennas
(the "spikes" you refer to) up on the roof of the car and indicates on
the "readout" in the car the direction the signal comes from. I have a
friend that owned one. He gave about $600 for it. It worked very well.
For $600 it would *have* to work well :). He bought the thing in about
1991, if memory serves.
Later I recall having seen an article in QST that detailed how to
construct such a device. It used 4 antennas, as I recall, and clearly
operated on the same principle as the commercial version my friend
owned. I don't remember just when I saw it. If you have back copies of
QST you can look in the "index" issues and perhaps locate the article. I
probably saw the article in the last five years, not earlier. I do know
that the article had to have been in QST since that is the only ham mag
I have subscribed to in the last few years.
Maybe someone else here can zero in on a better date for the article.
... Never pet a dog that's on fire.
--- PPoint 2.00
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