EDACS REPEATERS
2-18
Tx Limiting
Transmitter modulation limiting.
The Tx Limiting test measures the level of carrier deviation from the repeater transmitter for
differing levels of AF input, thereby establishing the effectiveness of the deviation limiting circuits
of the transmitter.
The test fails if the deviation level is above the prescribed limit.
The Service Monitor adjusts the level of the AF generator until the repeater generates the nominal
modulation level.
The Service Monitor then increases the AF level by the overload factor and checks that the result
from the repeater is below the limit.
Failure messages are:
*FAIL* NO MODULATION No modulation has been received from the
repeater.
*FAIL* ABORTED BY USER User halted program before test was complete.
*FAIL* UNSTABLE DEMOD Demodulated signal was not within 5% after 3
readings or 1% after 10 readings
*FAIL* LOW MIC I/P SENS AF level required to set the transmitter to reference
modulation level was to high to overload by the
factor given.
Tx Compression
Transmitter modulation compression.
The Tx Compression test measures the RF carrier deviation from the repeater at two levels to test
the operation of the compression circuits.
The test fails if the compression ratio is outside the tolerance limit.
The Service Monitor adjusts the AF level until the repeater generates the nominal modulation
level, then increases the AF level by 10 dB and measures the modulation level. The AF level is
then decreased by 20 dB and the modulation level measured.
The compression ratio is the ratio of the two measured modulation levels.
Failure messages are:
*FAIL* ABORTED BY USER User halted program before test was complete.
*FAIL* LOW MIC I/P SENS AF level required to set the transmitter to +10 dB
modulation level was to high to overload by the
factor given
*FAIL* NO MODULATION No modulation has been received from the
repeater
*FAIL* UNSTABLE DEMOD Demodulated signal was not within 5% after 3
readings or 1% after 10 readings
Rx SINAD
The Rx SINAD test measures the SINAD level of the signal received and demodulated by the
repeater.
The test fails if the SINAD level is below the prescribed limit.
The Service Monitor RF carrier is modulated at a frequency of 1 kHz at the nominal modulation
level. The demodulated audio from the repeater is fed to the AF INPUT of the Service Monitor,
which measures the Rx SINAD.
Failure messages are:
*FAIL* OUT OF RANGE SINAD level is below the prescribed limit.
*FAIL* ABORTED BY USER User halted program before test was complete.
*FAIL* LOW DEMOD LEVEL Receiver audio level <5 mV
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