TT26 ADS-B Transponder Installation Manual
24 January 2017
01633-00
Issue AC
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16
Trig Avionics Limited
5.5.5
Squat Switch Input
The Squat switch input allows the transponder to automatically switch between
Airborne and Ground modes, and affects both the Mode S reply behaviour and
the ADS-B reporting behaviour. The input will be asserted when the voltage to
ground is pulled below approximately 4 volts. The logical sense of the input
can be programmed to be either active low or active high.
On an aircraft with no appropriate squat switch circuit this input should be left
unconnected, and the transponder programmed to ignore the input.
5.6 D Connector Crimp Terminals
The 25 way connector supplied with the TT26 installation kit are MIL standard
versions of the popular sub miniature D type connector family, and use
individual crimp terminals and a receptacle. The MIL specification for this
family of connectors is MIL-C-24308. We supply crimp terminals because
these are more reliable than soldered connections, and are easier to assemble
in-situ in an aircraft, where soldering is impractical. They also allow
individual wires to be removed and replaced in a receptacle without replacing
the whole connector.
The socket contacts used in the 25 way connector conform to MIL part number
M39029/63-368, and are suitable for wire gauges from 20 to 24 AWG.
These contacts are widely used in avionics installation, and there are many
tools available on the market that will reliably crimp them to the wiring.
Because the contacts are a MIL standard, there is also a MIL standard for the
crimp tool, although other proprietary solutions are also available.
The MIL reference for the basic style of hand tool is M22520/2-01. This style
of tool can crimp many different contact types, and relies on interchangeable
"positioners" to hold the actual contact in use. The MIL reference for the
positioner that you need for the crimps we supply is M22520/2-08.
Any tool that complies with these references can be used to crimp these
contacts. One of the most popular vendors of these small hand tools is Daniels
Manufacturing Corporation (see www.dmctools.com). Their AFM8 hand tool
complies with M22520/2-01, and their K13-1 positioner is M22520/2-08
