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Winter 2005 Issue |
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DFing a Lifesaving Transmitter |
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The author (left) and
Ritch Williams, KA9DVL, try |
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I was amazed to see a foxhunter on the front page of the November 20, 2004 edition of the Elkhart Truth. On closer inspection, it turned out to be a picture of Captain Ron Biller of the Bristol, Indiana police department trying out a tracking device that is part of Project Lifesaver. I guess he really is a foxhunter, just not a ham, as far as I know. The system was designed five years ago by the sheriff’s department in Chesapeake, Virginia. It’s a system that has been in use for decades in pursuits such as ham radio and wildlife tracking (see the May 1998 issue of QST). It consists of a 3-element Yagi antenna connected to a receiver that is worn on a neck strap. The tracking device is used to track persons such as Alzheimer’s patients who might have wandered off. The patient wears a transmitter about the size of a wristwatch. It is worn on the wrist and transmits a short carrier about once a second and lasting about 50 milliseconds. The unit costs $263 and will transmit nonstop for a month on one battery. The battery costs $15. The transmitters operate on many different frequencies, from 215 MHz to 216 MHz. This allows searchers to distinguish between one patient and another. The local organization is called Triad. See the sidebar for more on Triad and Project Lifesaver. The Monday after I saw Ron Biller’s photo, I got a call from Jim Kehr, N9DUZ, about a missing transmitter from Project Lifesaver. I couldn’t understand why they needed me, when I had just read about the tracking devices two days before. Jim told me to call Captain Brad Rogers of the Elkhart County Sheriff’s Department; he also happens to be co-chair of Triad. Captain Rogers told me about a demonstration that had gone wrong. Triad had put on a training exercise on November 17–19. Several of the wristband transmitters had been deployed, and Triad members were able to go looking for them with the aid of the aforementioned tracking devices. All but one of the transmitters was found. One of them had become submerged in a lagoon on the edge of the Elkhart River. The water was only one foot deep, but the silt under the water extended for what seemed like forever. Hip waders were tried before the depth of the silt was discovered. A boat with a metal detector was tried, but the transmitter was never found.
The transmitter with its o-ring seal was still
transmitting, but Triad had no way to direction find the unit under water.
The best they could do was find a general location in the river where the
transmitter was submerged. I was amazed to hear that a signal was able to
propagate through the water well enough to be heard above water. Click here to return to Winter 2005 highlights Click here to subscribe to VHF _________________ © Copyright 2005, CQ Communications, Inc. All rights reserved. This material may not be reproduced or republished, including posting to a website, in part or in whole, by any means, without the express written permission of the publisher, CQ Communications, Inc. Hyperlinks to this page are permitted.
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