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Bird AT-400 Antenna Tester
40
ROM, EEPROM, RAM, A/D, TEMPR, PLL Test Fails
Ensure the results are valid by repeating the self test or
turning the unit off then back on. If the problem persists
return the unit for service.
Stuck Keys Test Fails
If any characters other than 0 are displayed next to stuck
keys during power up test, perform the keypad test on
page 36 of this section. Remember, if a key is depressed
during power up to display the power up test results it is
normal for other characters to be displayed. If the key
remains stuck return the unit for service.
“Noise” is Displayed During Testing
The Antenna Tester measures background noise to
determine if nearby signals could cause an erroneous match
measurement. Power down all nearby transmitting
antennas. All interfering signals must be removed before
resuming measurement.
Antenna Tester indicates a Perfect Match
When measuring the match of an antenna in a high RF
environment, the Antenna Tester indicates a perfect match
(i.e. VSWR = 1.00, Return Loss = -32 dB, or Match Efficiency
= 100%). This is caused by the coupling of interfering signals
into the Antenna-Under-Test. If sufficiently strong, the
interfering signals can over-power the measurement signal
inside the Antenna Tester. Normally, this results in
degraded measurement accuracy. Bird Antenna Testers
minimize this effect by measuring the interfering signal
during the time between match measurements. The inter-
ferer magnitude is subtracted from the magnitude of the
measurement signal. For relatively small interferers (i.e.
interfering signal smaller than the measurement signal),
this technique yields approximately 10 dB better rejection. If
the interfering signal becomes larger than the measurement
signal, the correction output approaches zero, corresponding