TT31 Transponder Installation Manual 1 February 2010
00455-00 Issue AJ
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5.5 Interface Details
5.5.1 Power Input
The power supply can be 11-33 Volts DC; no voltage adjustment is required. Contacts 11 and 12 on the
24 way connector are both available as power inputs. This is for compatibility reasons only – internally
the two are connected together, and in most installations only one need be connected to the power
supply.
Use a 3 Amp circuit breaker for power supply protection to the TT31.
5.5.2 Lighting Bus Input
The TT31 will adjust the brightness of the front panel switch lighting according to the voltage on the
lighting bus input. Two lighting bus inputs are provided on the 24 way connector to accommodate
aircraft with 14 Volt or 28 Volt lighting systems. When the lighting bus operates at 28 Volts, connect
the bus input to contact 3, and leave contact 2 unconnected. When the lighting bus operates at 14 Volts,
2. In this case contact 3 can be left unconnected, but for backwards
detected, the TT31 will automatically control the front panel lighting based on
uppression allows two or more transmitters on adjacent frequencies to inhibit the other
mmonly used between
n avoidance systems.
utual suppression interface on the 24 way connector. The Suppress
n aircraft with simple DME systems and no other suppression
ts.
n
s and Output
Gray code altitude input, or serial RS232 altitude input. Both of
altitude encoder you are using offers both, we
an only
– you
for D4. In an aircraft with a service ceiling below 30,000 feet input D4 will never be active,
and can safely be left unconnected.
The serial encoder input uses RS232 input levels. The communication should be 9600 bps, no parity.
connect
the bus input to contact
compatibility may also be grounded instead with no effect.
If no lighting bus input is
the ambient light sensor.
5.5.3 Mutual Suppression
Mutual s
transmitters when one is active to limit the interference effects. It is co
transponders and DME systems, and between transponders and collisio
The TT31 provides two styles of m
input on contact 9 is typically used i
requirements. It is an input only, and is active whenever the input is greater than approximately 5 Vol
The Suppress I/O on contact 4 is an ARINC compatible suppression bus interface, which acts as both a
input and an output. The TT31 will assert this signal when it is transmitting, and can be suppressed by
other equipment that asserts the signal. The TT31 will drive approximately 24 Volts on the output
(independently of supply voltage), and will treat the input as active whenever the bus has greater than
10 Volts.
5.5.4 Altitude Input
The TT31 can use either a parallel
these interfaces are on the 24 way connector. If the
recommend using the RS232 serial input. Serial formats allow a higher resolution altitude
representation that can be used by Mode S interrogations, whereas parallel Gray code format c
represent altitude to the nearest 100 feet. You must choose between serial or parallel formats
should NOT connect both. If a parallel encoder is connected the TT31 will always use that as the
altitude source even if a serial encoder is also connected.
The parallel encoder inputs are active when the voltage to ground is pulled below approximately 4
Volts. The TT31 includes internal isolation diodes which prevent the unit from pulling the encoder
lines to ground when the transponder is switched off. The TT31 can therefore share the altitude inputs
with other devices without needing external isolation.
Parallel output altitude encoders intended for operation below 30,000 feet may not have a signal
connection
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