Logic Interface; Power Supply - Tait TM8000 Series Accessories Manual

2.8.2

Logic Interface

2.8.3

Power Supply

28 TMAA01-01 Line-Interface Board
The audio interface is capable of using a two- or four-wire interface, so a
tap is taken from one side of the balanced line out and is feed directly into
the line input level control (RV3). When using a four-wire interface, the
signal comes in through a second isolation transformer, T2. T2 is terminated
with 600Ω and also acts as a voltage divider. This means that the signal level
at RV3 will be identical to the level at RV3 when using a two-wire interface.
To achieve the required output level the non-inverting AC amplifier (U7)
has a gain of 10, which provides the necessary 13dB of gain. The output of
the amplifier is AC coupled into the AUDIO_TAP_IN line (pin 6 of SK2).
The line-interface board is able to provide simple interface solutions with
other radios. Logic is used to control keying of both radios as well as
providing time delays to prevent squelch or cycling problems. The logic uses
gates rather than discrete components.
The choice of which input controls BUSY/GATE can be selected using
switches 3 and 4 of S1, while the sense of BUSY/GATE (pin 12 of SK1) can
be selected using switches 5 and 6. Switch 7 accommodates either a two-
line keying system or a single bi-directional keying line.
The comparators (in U1) operate off a single sided regulated 5V supply.
The power supply for the line-interface board comes from the radio via
the internal options connector and is a 13.8 V switched supply. Digital
logic components are used in the line-interface board so there is a 5 V
regulator provided.
Initially the 13.8V from the radio is filtered and used for the audio line
driver (U5) with reference to analogue ground. This 13.8V is also used to
supply the 5V regulator, which is filtered separately for either 5V digital or
analogue devices. A simple voltage divider is used to provide a 2.5V half-rail
for the digital and a 2.2V rail for the analogue sections.
TM8000 Mobile Radio Accessories Manual
March 2004 © Tait Electronics Limited