ST 500 "Piranha" Operation Manual: Use Guidelines
70
Case 4
Pair 3-6
There is no voltage. The test sound
cannot be heard in the audio output.
An electret microphone is connected,
with "phantom" power supply from the
telephone line and signal transmission
over wires #4 and #5. The microphone
must be located.
Pair 4-5
The voltage DC 26 V. The test sound can
be heard in the audio output.
Microphone localization algorithm is described in 9.5.
9.4.2. ACTIVATION OF ELECTRET MICROPHONES IN AN ANALOG TELEPHONE LINE
In order to detect an electret microphone having no power supply, bias voltage must be
applied to the circuit.
The initial state -
the connection scheme, circuit type, and pin numbers are the same as
described in 9.4.1.
Search algorithm:
1. Disconnect the circuit(branch) from the PBX.
2. Turn on the test sound source in the room.
3. Set the gain at 0 dB.
4. Set the bias v30 V.
5. Activate the AUTOMATED mode ("F4").
The device will start going through all the possible paired combinations, pausing at each table
line while the corresponding pair of cores is being tested; in the meantime, the operator can
listen to the received signal.
If the sound from the test sound source can be heard in the headphones, it means an electret
microphone is detected, and it will be necessary to locate it.
After all the combinations have been tested, scanning will stop.
If the test sound has not been heard in the headphones, search should be repeated in the
AUTOMATED mode, with reversed bias voltage (-30 V).
Recommendations:
If the test sound can be heard during testing, it is probable that the microphone is planted
in the telephone set. To make sure, disconnect the telephone; if the test sound can no
longer be heard, the eavesdropping device is in the telephone.
Any detected signals that have no relation to the test sound should be analyzed with
oscilloscope or spectrum analyzer.
9.5. LOCALIZATION OF THE SIGNAL SOURCE DETECTED BY THE "WIRED RECEIVER" OR
"LOW FREQUENCY AMPLIFIER" CHANNEL
9.5.1. ACOUSTIC METHOD
The acoustic localization method is applied only when an
"open transmission channel"
of
the eavesdropping device is detected. To implement the method, two operators are required. One
of them moves the test sound source around the room, the other operator controls the level of
the received signal using the ST 500.
