Re: [IRCA] Electronically steerable receive antenna

[AM-DXer@xxxxxxxxx (Patrick Griffith, N0NNK / WPE9HVW)]

It's the same thing as the 4 whips in a square you see mounted on police
cars for DFing the "tags" or transmitters hidden in the money packs that
the banks give the robbers. 
Chris
////////
I'm not so sure that this is the same technology. The technology with
the 4 whips on police cars is a proprietary system owned and provided to
law enforcement agencies by LoJack Corporation. The FCC allocated
173.075 MHz to this system on a nationwide basis and presently only
authorizes it's use with stolen vehicle recovery systems (SVRS). It can
not be used for die pack transmitters, etc. The FCC regulations are very
specific about this. There was a recent proposal by LoJack to extend the
authorized use of that frequency for other purposes which may include
die pack transmitters. But that proposal has not yet been approved.
Check out www.freqofnature.com/index.php?m=Common8p=LoJack for more info
on this system and the FCC regulations governing it.

The LoJack receivers in police cars electronically rotate the array at
high speed and use the doppler effect to identify the direction of the
incoming signal. Until recently I had a private version of this system,
complete with the 4 whip antennas, in my personal vehicle. As a member
of the Front Range Electronic Direction Finders, a ham radio based
volunteer search and rescue organization here in Colorado, I used it to
track the Emergency Locator Transmitter beacons on downed aircraft.

I may be wrong, but my guess is that the DX Engineering receive system
operates more along the lines of an AM broadcast station directional
antenna system using line phasing to produce the directional effect.

Patrick Griffith, Westminster CO
http://community.webtv.net/N0NNK/
http://community.webtv.net/AM-DXer/

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