TB7100 Installation and Operation Manual Preparation for Operation 117
© Tait Electronics Limited December 2005
4. Set the RF output level to -70dBm.
5. Verify that the busy LED on the front panel of the base station turns
on but the Rx gate LED on the CTU does not turn on, and no audio
output is detected from the balanced line output.
6. Modulate the carrier with the required subaudible signalling.
7. Verify that the Rx gate LED on the CTU turns on, and that the 1kHz
audio tone is detected by the test set, and that the measured distortion
level is within the receiver specifications.
8. Turn off the subaudible signal and check that the audio output mutes
again.
Note If high distortion is measured, it is likely that the subaudible signal
is not being filtered out. Verify that the receiver is programmed
with the correct audio tap out point.
7.10.3 Multiple Subaudible Tones
The base station cannot decode multiple subaudible tones on a single
channel. This can be overcome by two methods:
Method 1 1. Third-party equipment is available that can be connected to the base
station to perform the decoding and regeneration of multiple tones.
2. The base station repeater can be configured to simply pass through
any subaudible tone.
Method 2 1. The receiver must not be programmed with any subaudible tones in
the channel table.
2. The Rx tap out point in the receiver (Programmable I/O audio tab)
must be left as the default value of R4. This means that a incoming
tone/code is not filtered out by the receiver.
3. The transmitter must be programmed not to generate any subaudible
tones.
4. The Tx Tap In point in the transmitter (Programmable I/O audio
tab) must be left as the default value of T8. This means that a
incoming tone/code is not filtered out by the transmitter and will be
re-transmitted.
Potential Problems 1. The Rx gate may close before end of reverse tone burst (RTB).
This means the re-transmitted RTB may be shorter than incoming
RTB. A Tx tail (soft off) should be added to overcome this.
2. There is no security for repeaters, as any on-frequency transmission
will be repeated, even if it has no subaudible tone.
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