TB8100 Installation and Operation Manual Functional Description 45
© Tait Electronics Limited June 2005
Although the PA and PMU modules provide the power and ground for their
respective fans, the fan rotation detection is performed in the control panel.
The result is then read and processed by the reciter via the I
2
C interface.
The PA and PMU do not know if their fan has been correctly enabled,
however, if there is a fault in the fan circuitry, each module is protected from
overheating by its internal foldback circuitry.
In a dual base station, the fan rotation sensors report only to the currently
selected base station. The other base station will conclude that the fan is not
working and generate false alarms. We therefore recommend that you
disable all fan failure alarms (refer to “Dual Base Station System” on
page 38).
Speaker Signal Received audio can be sent from the reciter to the control panel. This
function is controlled by the speaker button on the control panel. The audio
signal is then amplified and passed to the control panel speaker for
monitoring purposes.
The audio output impedance of each reciter is fixed at approximately 2k
ohms. If two reciters are in the same subrack, either or both can drive audio
onto the bus. The system control bus will sum the two audio outputs
together and both will be passed through to the speaker. The summed audio
levels will vary, depending on the number of reciters in the subrack. The
volume range of the control panel speaker has been configured so that the
maximum number of reciters will still drive the speaker to the required
audio level.
Microphone Signal When you press the microphone PTT button, the reciter enables the
transmitter and connects the audio signal from the microphone input to the
modulator. The microphone PTT signal is read via the control panel using
the I
2
C bus and this then enables the transmitter. Note that the PTT
response times are slower than the response times for the TX_KEY input
from the system interface board.
The audio output from the control panel’s microphone is distributed to the
microphone audio inputs of each reciter. The low audio output impedance
of the control panel is not affected by the number of reciters connected as
the microphone audio inputs have a high input impedance.
Power and Ground The PMU provides power to the control panel via the reciters. Each reciter
has a series diode to ‘diode OR’ the power to the control panel, but not to
backpower a reciter that does not have a power cable connected.
Pin Allocations The subrack interconnect board at the front of the TB8100 subrack provides
a parallel interconnection between all connectors on the board.
The following table gives the pin allocations for the IDC connectors to the
reciter, PA and PMU, and for the D-range connector to the control panel.
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