On Tue, 15 Feb 2011 08:32:11 -0800 (PST),
" wrote:

This type of product is advertised almost everywhere that it helps you
avoid tickets etc. I imagine that it must transmit a signal on the
same freq. as the radar gun at the moment it receives the police
transmission. Even at low power can this still meet part 15 of the FCC
rules or any part for that matter? I happen to drive slowly but
millions of people don't. Can someone please tell me how it works? How
can something like this product which for all intents and purposes
"interferes with police business" be legal? Just wondering. Lenny
One approach was describe several decades ago in a 'build it
yourself' project in 'Radio Electronics' magazine.

Speed radar works by sending a high frequency pulse and comparing the
frequency of the returned signal to the original. The frequency shift
of the return pulse will be proportional to the relative speed of the
radar gun and the object generating the reflection.

The R-E article was for a 'radar gun calibrator'. By taking the
received signal, amplifying it, modulating it, and transmitting only
one of the sidebands, a synthetic 'echo' would be produced with the
precise frequency offset desired.

As far as selling them, don't bother. You can make more money by
selling tinted plastic license plate covers, claiming they will 'fool
photo speed enforcement cameras'. Of course, the real fool with be
the person sending you his money.

PlainBill