User's Manual

TT21 Transponder Installation Manual 19 January 2009
00560-00 Issue AA
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7. Post Installation Checks
Post installation checks should be carried out in accordance with your certification requirements.
These checks should include:
 Mode S interrogations to verify correct address programming.
 Verification of the reported altitude using a static tester.
 Where installed, verification of correct squat switch ground/airborne indications. In an
aircraft with a squat switch, setting the Mode switch to ALT when the aircraft is on the
ground should leave the transponder in GND mode; when the aircraft becomes airborne, the
mode should switch automatically to ALT.
 Interrogations to verify the receiver sensitivity. A Mode S transponder should have a
minimum triggering level (MTL) of between -77 dBm and -71 dBm. Failure to meet this
requirement usually indicates antenna or coaxial cable problems.
 Interrogations to verify the transmitted power. A Class 2 installation should have no less than
71 Watts at the antenna (and no more than 500 Watts). Failure to meet this requirement is
also generally due to antenna or wiring issues.
 Where installed, verification of the GPS position source and ADS-B outputs. Whenever a
valid position is received by the transponder and the transponder is in any mode other than
Standby, ADS-B Extended Squitters should be observed on the transponder test set.
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