User's Manual Part 2

T
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CAS / Part No. 9000000
SYSTEM DESCRIPTION AND INSTALLATION MANUAL
34-43-20
15 Feb 2003
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6--30
NOTE: The procedures that follow a re recommended for intermittent antenna system
failures or if the continuity tests have not identified a failed component in the
antenna system or if the flight crew detects an unacceptable visual discrepancy
between an intruder aircraft and its displayed location.
(8) If the displayed location of an intruder aircraft is believed to be in error, appropriate
ramp test equipment can be used to simulate intruder aircraft to check the suspected
discrepancy while on the ground.
(9) Remove the suspected TCAS directional antenna and terminate the antenna side of
the cable with a 50 ohm termination (Omni --Spectra Part Number 3102--6100--00 or
equivalent TNC jack with VSWR ≤1.15 : 1 ).
(10) Perform a thorough inspection for moisture or contamination of all coax cable
assemblies.
(11) Remove the T
2
CAS LRU and do a VSWR check on the coax cable from the T
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CAS
computer tray side. Use approved VSWR test equipment and operating procedures.
The measured VSWR should be less than 2.0 : 1.
(12) If the VSWR test fails, isolate failed antenna coax section. Remove/repair
appropriate cable and/or connector.
(13) An additional procedure for troubleshooting TCAS antenna system failure s is to
determine the RF insertion loss in the TCAS antenna coaxial cables. RF insertion
loss is equivalent to RF IxR (voltage) drop through the coax and is measured in dB
rather than volts. Each coax cable is required to have is 2.5 dB ( ±0.5 dB) of insertion
loss and the loss in all the coax cables must be within 0.5 dB of each other. Many
VSWR meters have a fixed RF source and can be used to measure RF insertion loss.
In this test, the VSWR meter is used to measure the loss up one cable and down the
other. The total loss should not exceed 6 dB.
NOTE: The VSWR/insertion loss meter should be set up for L--band frequencies
(approximately 1.0 GHz).
To perform an RF insertion loss test, do the following:
(a) Connect two of the TCAS antenna coax cables to each other at the antenna end
with a DC shorted coupler.
(b) Before any measurements a re taken on the antenna system, the meter and any
connectors/cables that are used to connect the meter to the TCAS antenna
system must be zeroed out. This is typically done with a calibration adjustment
on the VSWR meter.
(c) After the VSWR meter (and associated connectors/cables) have been calibrated
for 0 dB, connect the VSWR meter to the TCAS antenna coaxes under test (at
the LRU end). Measure and record the RF loss.
(d) Test different combinations of the TCAS antenna coax cables by connecting the
coupler (at the antenna end) to different coax cables. By process of elimination, it
can be determined if one of the TCAS antenna coax cables has excessive RF
insertion loss.