NON-LINEAR JUNCTION DETECTOR
45
5.3. NON-LINEAR JUNCTION DETECTOR (NLJD)
NJLD FUNCTIONAL DIAGRAM
5.3.1. GENERAL INFORMATION
The NLJD is intended for detection of the eavesdropping devices (including turned off and/or
faulty) connected to a cable.
The operation principle of the NLJD of the Analyzer is similar with an operation principle of a
usual NLJD. The built-in transmitter emitted the probing signal to the tested cable, and the
receiver fixes reflected signals at frequencies of second and third harmonics.
Existence of signals at these frequencies demonstrates presence in the cable of nonlinearity or
metal-oxide-metal (MOM) structure. If the level of the second harmonic exceeds the level of the
third harmonic, then with a high probability an electronic device is connected to the cable.
If the level of the third harmonic exceeds the level of the second harmonic, it is likely that a
MOM structure is present in the cable.
In practice, cases when a signal is received only at the frequency of the second or only at the
frequency of the third harmonic is quite rare.
Therefore, when signals are detected simultaneously at the frequencies of the second and third
harmonics (regardless of the ratio of their level), it is necessary to test these cable.
For the NLJD to operate correctly, the tested cable must be disconnected from all electronic
equipment.
Eavesdropping devices can be connected to the cable in parallel or in series (to break one
wire). Each pair of wires must be tested by two methods:
To search for parallel connections, the pair of tested wires must be broken at the far end
(idle mode).
To search for serial connections, the pair of tested wires must be closed at the far end
(short circuit mode).
When testing the multi-wire cable equipped with RJ45 connectors in the short circuit mode it is
necessary to use a special short-circuit socket
(Fig.1, item 15)
.
If at pair of wires there is voltage more than ±3 V, its test by means of a NLJD is impossible.
On the pair indicator (Fig. 50, item 2) the inscription "OVER" will appear. Such a cable must be
de-energized.
Turning on the NLJD is made from the Analyzer main menu (item 3.2).
The NJLD main menu is shown in Fig.37.
