[FedCom] GPS / Bird Dog question

[Steven Donnell]

The 8 block(limit) was the range of the signal from the beacon(Bird Dog) 
to the other units that were tracking it. When the beacon is installed 
under the suspect's vehicle, usually attached to the gas tank w/ a 
strong magnet, the range would be much less than in the test w/ the 
ant/beacon sitting on the dash. If the beacon was transmitting GPS data, 
the units tracking it would likely be have laptops that provides a map 
overlay.

The original Bird Dog used a beacon that transmitted a series of narrow 
pulses that were hard to detect w/ a typical receiver. The very limited 
duty cycle of the transmitter also provided very long battery life. The 
tracking receiver, which used a pair of whip antennas, could only 
provide left/right directional information, and signal strength. It 
could also tell if the vehicle being tracked was stationary, by way of a 
cpl of mercury motion sensors in the beacon. When the beacon sensed the 
vehicle was not moving, it changed the pulse pattern to alert the 
trackers, and reduced the rate of  transmissions.  About 15 yrs ago a 
newer generation of tracking receivers began to appear, similar to those 
used for LoJack tracking,  which included full compass bearing vectors 
which made tracking much easier and required less practice. Newer 
generation tracking systems use GPS, however one common problem is that 
in order for them to operate, the GPS(or at least the antenna) must 
"see" some portion of the sky in order to get a lock on a satellite.

DE WA1YKL
radio DF
RadioScan at aol.com wrote:
> Heard some interesting comms in the Philadelphia area today, which presented 
> a question that I have.
>
> The freq was 171.4375 and to capsulize it, one agent drove to a predetermined 
> location and sat.  At the same time, I heard that car talking to another, 
> with the other continuing to say, I don't pick you up yet.  At first, I thought 
> they were testing a transmitter and looking for the coverage area [from the 
> conversation].
>
> Then finally he said, "I got you know".  The other guy asked where he was and 
> after giving him an intersection, he said "that's good coverage, about 8 
> blocks".  Some other small talk about how the antenna is currently on the dash and 
> after it is installed, it may not have the same coverage  and then the puzzle 
> started -  He then says "This will save us from having teams out to follow 
> him, we can track him, without him seeing us"
>
> Then the one car says to the other "lets test it in motion and see if I can 
> track you - head back to the office and I will see if I can follow without you 
> seeing me".  They did this and every once in while the tracking car would call 
> out something, such as "You just made a right on 2nd street", etc.
>
> If it was a GPS tracking device, then why would it only have 8 blocks 
> coverage.  If it is a Bird Dog, my question is, do they now have a mapping overlay 
> type product, which lets you see the target on a map (like the GPS units do).  
> Any thoughts on this...?
>
>
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