Vector Signal Analysers

Digital eavesdropping and surveillance devices are commonly available for only a few hundred dollars, and may be easily built out of spread spectrum cordless telephones.

The Chinese, French, and United States government have all been using such devices for years. Dozens of these digital devices have been found in corporate offices, vehicles, and executives homes. These devices are being hidden inside other electronic devices such as computers, televisions, and copy machines.

The detection of a digital device becomes very difficult unless the equipment being inspected is opened and physically searched. These devices often operate with sub-milliwatt power levels, with a signal bandwidth often in excess of 1 MHz.

A Vector Signal Analyser (or VSA) is an instrument which allows modulation analysis of modern digital signals. The instrument is similar to that of an oscilloscope, however; the VSA allow the additional analysis of both the In-phase (I) and Quadrature-phase (Q) components of a signal. Modern eavesdropping devices which utilize vector modulation techniques often may only be identified by examining the I/Q components of a electromagnetic anomaly.

Components emitted by AM, FM, BPQSK, QSK, QAM, Pulse, and other modulations types are easily identified and evaluated. This will identify all but the most exotic digital eavesdropping devices. High bandwidth eavesdropping devices would be detected by the use of compressive or Bragg Cell receivers.

A VSA typically requires a dual I/Q signal input, which is generally only available on specialized radios (Rockwell, Condor, MACOM, or Watkins-Johnson), or modern spectrum analysers (such as the HP 71910A/P). The signal is then passed to the VSA which combines the signals into a complex quantum signal which exists only in the digital domain.

Complex signals analysis algorithms are then applied to the incoming signal to extract the modulation parameters. This will then permit the demodulation of most suspect signals.

The HP 89410A Vector Signal Analyser is rapidly gaining favor within the TSCM industry, and will probably become a mainstream TSCM instrument over the next few years.

The HP 8981B is also an excellent Vector Modulation Analyser, but has a very limited bandwidth. The unit is an analog instrument as opposed to the HP 89410A which is a digital unit.

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