CT Systems Wavetek 2500 - Page 44

3.4.5 Receiver Sensitivity with CTCSS Decoder and Decoder Bandwidth
Test
This test determines the amount of RF signal that is required to
unsquelch a receiver that uses a CTCSS decoder. The Bandwidth part
of the test determines the amount the encoder oscillator can drift
from desired CTCSS frequency and still unsquelch the receiver. Too
much decoder bandwidth can be a problem if wide enough to allow other
transmitters with tone frequencies near the desired to operate the
receiver.
This second test is sometimes called Tone Squelch Sensitivity.
Refer to Figure 3-7 for the following test procedure.
l) Connect the RF input (antenna port) of the receiver under test to
the "RF IN/OUT" jack on the Model 2500.
2) Select GEN mode and set the RF Output level to 0.1 uV.
3) Select AUDIO SYNTH .
4) Set the Audio Synthesizer to the subtone
the numerical keys followed by the ENTER
frequency in Hz using
key.
5) Put the receiver under test into Decode Mode and adjust its
squelch for threshold.
6) Adjust the Audio Synthesizer level control to 600 Hz deviation,
or to manufacturer's recommended deviation.
7) Turn off audio synthesizer by toggling the AUDIO SYNTH key.
8) Activate l kHz and adjust level to 3 kHz deviation.
9) Toggle AUDIO SYNTH back on.
10) Increase RF LEVEL vernier control until the - receiver just be-
comes unsquelched (l kHz tone is heard+ noise). Read the Re-
ceiver sensitivity from the RF level dial.
ll) Vary the AUDIO SYNTH frequency to either side of selected
frequencies in l Hz increments using the numerical keys followed
by the ENTER key. The difference between the frequencies at
which the receiver unsquelched at the last RF level setting is
the decoder bandwidth.
2500-MANUAL
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32
SECTION-3