TX56/56A and TX57/57A Installation Manual
5 April 2022
01776-00-01
Issue AD
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Trig Avionics
Page 39
The OBS system will automatically adjust the level to achieve the correct
sensitivity, but the individual instrument will need to be calibrated for bearing
accuracy at installation.
5.6.26
Power Input
The TX56 power supply can be 11-33 volts DC; no voltage adjustment is
required. The TX57 requires 22-33 volts DC. In both cases use a circuit
breaker with a minimum value of 5 amps for the communications radio, and a
circuit breaker with a minimum value of 3 amps for the navigation receiver.
In practice, higher value circuit breakers are often used, particularly if more
than one device is sharing the circuit breaker. If a circuit breaker with a higher
rating is used, the wiring gauge used should be increased appropriately.
The peak current consumption on transmit exceeds the current capability of a
single pin on the 25 way connector. Both power inputs must be wired, and at
least two ground returns must be wired. Use 20 AWG wire for the power
connection wires.
The Nav receiver power consumption is lower, and a single 22 AWG wire on
the 44 way connector is sufficient.
Note: The power consumption figures for the Nav/Com do not
include current taken from the switched power output, or from the
superflag outputs. If these outputs are used the current consumption
from those outputs should be added to the Nav/Com current
consumption when choosing wire sizes and circuit breaker capacity.
5.6.27
Ground Returns
There are only 3 ground pins on the 25 way connector, at pins 4, 9 and 17.
Two of these ground pins should be used for the power input leaving the other
ground pin for the audio grounds. Audio grounds should be connected
together with a fly lead connected to the remaining ground pin using the
ground screws on the mounting plate.
There are adequate ground pins on the 44 way connector to associate with the
signals from that connector. Do not try to supplement the Com radio audio
grounds by borrowing unused grounds from the 44 way connector, as this can
couple noise into the audio signals.
