Radar detector detector
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A radar detector detector (RDD) is a device used in areas where radar detectors are declared illegal.
Radar detectors are built around a superheterodyne receiver, which has a local oscillator that radiates slightly. It is therefore possible to build a radar-detector detector, which detects such emissions (usually the frequency of the radar type being detected, plus about 10 MHz for the intermediate frequency). Some radar guns are equipped with such a device.
VG-2 Interceptor was lastly the first device developed for this purpose, although more current technology such as the Spectre III (Stalcar in Australia) is now available. This form of "electronic warfare" cuts both ways and since detector-detectors use a similar superheterodyne receiver, many early "stealth" radar detectors were equipped with a radar-detector-detector-detector circuit, which shuts down the main radar receiver when the detector-detector's signal is detected, thus preventing detection by such equipment. In 1982 the US military funded a project, codenamed R4D (radar detector-detector-detector-detector), in order to develop a device capable of detecting radar detector-detector-detectors. This technique borrows from ELINT surveillance countermeasures. In the early 1990s, BEL-Tronics, Inc. of Ontario, Canada (where radar detector use is prohibited) found that the local oscillator frequency of the detector could be altered to be out of the range of the VG-2 Interceptor. This resulted in a wave of detector manufacturers changing their local-oscillator frequency. Today, practically every radar detector on the market is immune to the VG-2 Interceptor.
The Spectre III detected almost every radar detector certified for operation in the United States by the Federal Communications Commission as of December 2004. However counter technology has evolved rapidly, so that by July 2008, even budget radar detectors were able to avoid detection by the device. Then, in late 2008, the SpectreIV was released, citing improved range and reliability over the Spectre III.