[TenTec] radar

[Vic Klein]

Well, still pretty far OT, but here's the basic concept. The radar units
send a radio signal and then read the reflected signal back looking for the
difference in the "bounced" signal frequency and the transmitted frequency.
Objects moving toward the gun cause a Doppler shift up so the frequency
difference is read (and audio-range frequency) and displayed as a speed
after applying a calibration factor. As I understand the designs (not having
studied the schematics), the detector has to mask the gun frequency to keep
it from swamping the receiver and, sort of like generating SSB in your Ten
Tec radios, filters the carrier and the opposite Doppler shifted stuff as
well. So, the gun will read either higher-shifted frequencies (objects
moving toward the gun) or lower (moving away), but not both at once (like
USB vs. LSB). In order to test that the gun is working, a tuning fork (I
cannot recall the frequency, but it is audible) is struck and held in front
of the gun, which measures the speed of the fork moving toward the gun and
ignores it when it is moving away (or vice-versa). The fork frequency is
chosen to display 55 mph and would work when selecting either direction, of
course.

All that being said, many years back there was an article in some magazine
about the perfect radar-protection device. It was a transmitter, which
happened to be in a ham band for one common radar frequency, which was
offset from the standard police radar just enough so that whatever speed you
were going was displayed as 55 on the gun since it swamped the bounced
signal with a stronger one of a chosen frequency. Note, police use several
different radar frequencies as well as laser and timing devices, so this
would not really work these days, but it is an interesting theoretical
exercise.

Now, back to listening to the bands and waiting for improvements on my
trusty Paragon!

=Vic=
WA4THR

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From: 	"Gary Hoffman" <ghoffman at spacetech.com>
Reply-to: 	Discussion of Ten-Tec Equipment <tentec at contesting.com>
Date: 	Sun, 3 Jul 2005 15:31:36 -0400
List-post: 	<mailto:tentec at contesting.com>

Fascinating.  Can you elaborate on this calibration method.  Its nothing I
had ever heard about before. Thanks.

73 de Gary, AA2IZ