Bird Technologies AT-800-Manual - Manual (Page 68)

Bird AT-800 Antenna Tester
50
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 45. Remember, if a key is depressed dur-
ing 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 transmit-
ters. All interferers 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 cou-
pling 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 measure-
ment accuracy. Bird Antenna Testers minimize this
effect by measuring the interfering signal during the
time between match measurements. The interferer
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 bet-
ter rejection. If the interfering signal becomes larger
than the measurement signal, the correction output
approaches zero, corresponding to a perfect match.
Measurement results are not accurate under these cir-
cumstances. The remedy is to disable the interfering
source, if possible, or postpone the measurement to a
time when the interfering source is not operating.