Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1997-04-09
2000-02-01
Vu, Viet D.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
324 7619, 4551611, 4552261, G06F 1700
Patent
active
060212691
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of data processing, and has particular application in the collation and analysis of spectral data records (for example for surveillance counter measure work, such as the detection of bugs or for other applications, such as the detection of "leaky" data cables).
The usual way to detect bugs is via their transmissions. Two types of wide band scanning receivers are commonly used: amateur or defence markets, which excel at the detection of weak signals and are designed to give clear reception with superb selectivity; scanners have little selectivity, in the particular sense that they will detect signals from any transmitter within their designated band of coverage, either instantaneously or within a very short scanning cycle.
ICOM 7000 and 9000 series and Watkins Johnson Miniceptor receivers are examples of the first category of receiver, and the Datong Ranger 2+ and Audiotel ECM are examples of the latter.
Use of an ICOM-type receiver relies heavily on the skill, patience and concentration of a skilled operator to listen to each voice channel in the entire spectrum covered, typically 0-2000 MHz. To do this with maximum efficiency, the receiver must be set to move through much of the band in increments of not greater than 10 KHz (5 KHz would be optimal).
In a single scan, an operator has to listen momentarily to the audio content of each discrete channel, say 10,000 to 200,000 channels, the exact number being dependent on the scan pattern selected. Were such a scan to take three hours, the operator could not spend an average of more than a second on each channel. In that time the operator is required to become aware of a signal on any channel, and make a decision as to whether or not it is relevant to his task. With the finest grain of scan, this time would be impractically shortened.
Accordingly operators are forced to use scan patterns that leave holes in the cover. Even were there no holes in the cover, the operator is faced with an impossible task, since he must determine whether or not an emission of which he cannot understand the content is a security threat. Accordingly, other than for the simplest and plainest clear voice signals, the operator cannot always do so. Consequently, his opinion at the end of each complete spectrum scan is little more than a "best guess".
Though not as uniformly sensitive across their range as quality communication receivers, the harmonic scanners work faster and with an improved level of assurance. Typically, a single spectrum scan will take no more than ten minutes. In that scan, because of the harmonic effect (explained hereinafter), a bugging transmission at 25 MHz will be seen by the receiver (Ranger 2+) three times. At 100 MHz it will be seen six times, and over one hundred times at 1000 MHz.
The harmonic receivers are normally operated in one of several modes for detecting an active bug: and then applies three or so demodulation techniques to radio signals that it detects, looking to recover its known audio signal. This can work reliably, but only against transmitters using one of the forms of signal modulation covered. signal it receives, or may alert to any signal above a set threshold strength, whether the receiver can cohere it or not. (Some single channel receivers also have this facility.) This can be a useful means of detection but is has serious limitations. For it to be effective, the bug must be the strongest, or almost the strongest, signal received. Under operational conditions where the spectral environment is as "dirty" as central London, Tokyo or Paris, this technique produces an unacceptable number of false alarms. Constant false alarms demotivate the operator to follow up each one rigorously; this results in a very substantial chance anything other than a simple and relatively low frequency bug simple being passed over. receiver, except that the operator listens to the content of many harmonics at once. This mode is much inferior (except in speed) to a single channel receiver.
However, none of the receivers,
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