Re: [IRCA] Electronically steerable receive antenna

["Chris Black" <n1cp@xxxxxxxxxxx>]

I used to listen to the police frequencies (I also knew many in Public 
Safety through my Amateur Radio Emergency Service activities) and I know for 
certain that they, at least at one time, used their car-top arrays for the 
die-pack DFing, as I would listen to them converge on a suspect. Perhaps 
your information is now the most current and that is no longer the case.

Chris
----- Original Message ----- 
From: "Patrick Griffith, N0NNK / WPE9HVW" <AM-DXer@xxxxxxxxx>
To: <irca@xxxxxxxxxxxxxxxx>
Sent: Monday, November 20, 2006 5:47 PM
Subject: Re: [IRCA] Electronically steerable receive antenna


> 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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