User's Manual

TY91/TY92 VHF Radio Installation Manual 11 April 2012
00839-00 Issue AA
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26 Trig Avionics Limited
5.10 Wiring Considerations
5.10.1 TC90 Interconnect
The connection from the TY91/TY92 VHF radio to the TC90 uses a minimum
of six (6) signal lines; the TMAP pair, the Power and Ground pair, and the
Remote On discrete line plus associated ground line. In a certified installation
the normal wire choice would be Tefzel hook-up wire. Wire of 20 AWG is
more than adequate for the task; in installations where weight is an issue, wire
of 22 or 24 AWG can also be used. Where lighter wires than 20 AWG are
used the individual wires should be laced together for support.
The TY91/TY92/TC90 interface was tested and certified using unshielded,
untwisted wiring, and that is sufficient for a certified installation. There may
however be technical benefits of improved electromagnetic emissions and
susceptibility to and from the VHF radio system if the two wires of the TMAP
pair are lightly twisted together – one twist per 1 to 2 inches is appropriate.
This may reduce interference and break-through on adjacent audio wiring if it
is not possible to route them separately. For tidiness and consistency the other
pairs in the bundle can also be twisted, but there will be no particular
difference in behaviour.
The distance between the TY91/TY92 VHF radio and the TC90 controller is
limited by the impedance of the wire between them. The TC90 is powered
from the TY91/TY92, not from aircraft power, and therefore the acceptable
voltage drop in the power line is what limits the distance.
The TC90 needs an impedance of less than 1 ohm in the power line for
satisfactory operation. The following table gives guidelines for typical aircraft
hook-up wire. Note that different brands may vary – check your supplier for
details.
Gauge
Ohm/km
Length for 1 Ohm
20 AWG
35
28.4 m
22 AWG
64
15.6 m
24 AWG
99
10.0 m