VLF Test Transmitter Built for NYC Search
Sep 17, 2001 12:00 PM, By Chriss Scherer, editor
Quincy, IL, and - Sep 17, 2001 - Like many office buildings, the employees in the World Trade Center were issued security cards to permit access into various parts of the building. These access cards, sometimes called Smart Cards, transmit a data burst when excited by a specific radio frequency. With this in mind, technicians at Motorola began developing a system that may be useful in locating people in the rubble of what was once the World Trade Center.
Greg Buckwald of Motorola worked with Broadcast Electronics in the early development of the AM C-QAM system. Because of his existing relationship with Broadcast Electronics, he called on the company to work on developing the location system. A Broadcast Electronics AM500A was modified to transmit at 125kHz.
Smart Cards are made to respond to the 125kHz signal by responding with a data burst on 187.5kHz. The system will be used to send a signal through as much as 10 feet of rubble while a listening system monitors for the resulting data bursts, indicating the presence of a card and, hopefully, a person.
The modified transmitter was built in Quincy. Jerry Westberg and Jay Linderer of Broadcast Electronics drove it to Motorola in Schaumburg, IL near Chicago on September 14, where it was tested. The unit was shipped to New York City on September 17, where it was demonstrated to the New York Port Authority. Pending the results of the test, the unit will be put into use later on September 17.
The transmitter power output is set at 350W, which should penetrate up to 10 feet of rubble. The transmit antenna is a loop about three feet in diameter. The power level being used is to accommodate the antenna, which measures about 3 ohms +j300 - hardly an ideal match, but good enough to send the carrier signal. The transmitter rns on 220 volts and will be powered by a generator on site.
If the tests go well, Motorola and Broadcast Electronics may build a second unit for use at the Pentagon.