SECTION 6: CONDUCTING A SWEEP
99 REI OSC-5000E
Also the OSCOR can be taken outside, 200 ft from the building, to investigate the signal
strength in the outside environment. If the signal is still strong, then the signal is common
to the environment and probably not an eavesdropping device. If a signal is unique to a
building, it is important to determine the signal origin. If the signal appears to be stronger
in one office, use the locator probe to locate the signal’s origin (see page 59 Locating RF
(500KHz to 3GHz).
Transmitter Harmonics
Most RF bugging devices are designed to transmit at a single, primary frequency also
called the fundamental frequency. However, due to size and cost constraints, most RF
bugging devices do not contain a sufficient amount of filtering and, therefore will radiate
at several harmonically related frequencies. These recurrent signals are typically at some
multiple of the fundamental frequency. For example, a bug that is radiating at 110 MHz
may also radiate at 220 MHz, 330 MHz, 440 MHz, or 550 MHz. The signal strength of
each successive harmonic signal will normally decrease with increased frequency and
eventually diminish completely. With the OSCOR scanning in the Automatic Mode, each
harmonic signal will be detected as a new threat. If the harmonic is stable and accurate,
OSCOR’s automatic software will calculate and label the presence of the harmonic (H1,
H2, etc.).
Some transmitting devices containing a lower frequency oscillator and multiplier generate
sub-harmonics at frequencies multiples of the internal oscillator not fundamental
frequency. For example, one wireless microphone on the commercial market that works
well as a bugging device has a fundamental frequency of 155 MHz, but also radiates at
165 MHz, 175 MHz, and 185 MHz.
Harmonic signals increase the probability of detecting a transmitter, because when the
OSCOR is scanning in the Automatic Mode, harmonics provide additional opportunities
to detect a single transmitter. If you have multiple threats detected, examine the
relationship between the frequencies to determine whether the additional signals are
harmonic or multiplier frequencies.
Unintentional Radiators
Many things that are not designed to be radiators can cause false readings. Most
unintentional radiators have very little range and are easy to identify by one of several
methods. Since unintentional radiators have little power, the radiated signal should be
very localized. The location of the radiator may be found using the locator probe. It is
also easy to turn off various pieces of equipment in the environment to determine if a
signal stops. Some examples of unintentional radiators, the expected signal, and their
likelihood are provided in Figure 67 Unintentional radiator table.
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