Miata Mailing List: November 1994, Message #87
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   From: a.mccombs3@genie.geis.com
Subject: Re: Radar Jammers
   Date: Thu, 3 Nov 1994 10:55:56 -0500

I believe we're skirting around the edges of the Real Truth RE:
electromagnetic signal transmissions, but we're not spot on yet.  The FCC
(Federal Communications Commision) requires most transmitters to be
licensed, since they send out a signal.  There are no licensing requirements
for receivers, since they can't bugger up the ether with signals.  (Well,
theoretically anyway, although many receivers emit side signals of various
sorts. That's how radar detector-detectors work, by picking up the faint
emitted electromagnetic energy from a radar detector, while it is doing its
work.)  There are exceptions to the rule, e. g., very low powered devices
like garage door openers, walkie-talkies, cordless phones, etc.  It also
depends upon the frequency of the signal.  At night you're all transmitting
30 to 60 watts or so of electromagnetic energy primarily in the visible and
infrared ranges, assuming you drive with your lights on.
 
OTOH, it's perfectly acceptable to have a transmitter capable of
transmitting on the same frequencies as other transmitters in the area.
Aviation radios do this all the time, but it's like a party line, in that
you wait till the other guy (OK, or gal) finishes transmitting before you
step in.  It's also possible for several people to be transmitting at once
on the same frequency with no problems, depending upon line of sight and
where the transmitters are, signal propagation, etc.
 
So:  what about radar?  The cops are required to have an FCC license for
such a device capable of transmitting on those frequencies.  (I understand
that radar tickets have been beaten in court by showing that the agency
using the radar transmitting gun did not have a current FCC license for it,
and was thus violating Federal regulations.  Hence, the evidence for
speeding was gathered illegally.  Case dismissed.)
 
However, the same rules apply for radar jammers.  A true, active jammer
transmits a signal of (essentially) the same frequency as the radar gun,
which the radar gun receives and interprets as a return echo.  Obviously,
the jammer signal has to be stronger than any incipient reflected signal, to
override that reflected signal.  By fiddling with the pulse width, one can
make the radar gun receiver "think" that the car is going slower than it
really is.
 
Accordingly, it would appear that since one is using a microwave transmitter
when one is using a true jammer, that one would need an FCC station license
for the thing.  I'd guess that you have two chances of getting one:  Slim
(very!) and none.  OTOH, maybe I'm missing something here, and there is some
"cutoff" below which power output in the radar frequency range, one doesn't
need a station license.  I'm not sure on this.  If so, then jammers should
be legal, at least insofar as the FCC is concerned.  (Another question is
how can states ban passive receivers - radar detectors - when the Federal
Govt., through the FCC, has explicitly upheld the rights of citizens to
receive transmitted signals, in their regulations.  I leave it for someone
else to test the legal waters on this one.)
 
So after all this, the bottom line is, no, you can't transmit
electromagnetic energy without a license from the FCC, with exceptions.
Does an active transmitting jammer fall within the exceptions?  I'm not
sure, but considering the ways of Govt., I'd be surprised if it did.
 
                                                --Jack M. & Kansei--