12-6 MTR3000 Performance Check or Testing: Verifying Receiver Circuitry
12.3.3 Verifying Receiver Circuitry Procedure
1. Connect test equipment by performing Steps 1 to 3 shown in Figure 12-2.
2. Using the CPS, disable PL and unsquelch the Receiver such that noise is heard through the
external speaker. If no audio is heard, suspect the following:
• Faulty Receiver Module
• Faulty Station Control Module
• Aeroflex 3900 Series Communications System Analyzer is outputting a carrier signal without
modulation
3. Set Aeroflex 3900 Series Communications System Analyzer to generate a 1.0 μV (-107 dBm)
FM signal at the Receiver frequency, modulated by a 1 kHz tone at 3 kHz deviation for 25 /30
kHz channel spacing, or 1.5 kHz deviation for 12.5 kHz channel spacing. The 1 kHz tone
should be audible through the external speaker. If no audio is heard, suspect the following:
• Faulty Receiver Module
• Faulty antenna-to-Receiver preselector RF cable (for the base station/repeater with external
metal preselector)
• Faulty Aeroflex 3900 Series Communications System Analyzer-to-station RF cable
• Faulty Antenna Relay
• Faulty Preselector
4. If audio is heard, connect the external speaker RJ-45 jack to the Oscilloscope input BNC
connector, as shown in step 4 of Figure 12-2.
5. Using the CPS, increase the audio volume to maximum. Measure the audio level using the
Aeroflex 3900 Series Communications System Analyzer.
• Audio level should measure approximately 0.75 to 1.5 Vpp. If not, suspect faulty SCM.
6. Change Aeroflex 3900 Series Communications System Analyzer injection signal level to the
noted levels in Table 1-4.
7. Measure the Receiver 12 dB SINAD sensitivity. Set the signal strength of the communications
analyzer to the rated sensitivity according to Table 1-4.
• If the SINAD level is less than 12 dB, suspect faulty Receiver Module or SCM.
8. This completes the Verifying Receiver Circuitry test procedure. If all displays and
measurements are correct, the Receiver circuitry may be considered to be operating properly.
Remove test equipment, restore the base station/repeater to normal service, and (if
applicable) return to the troubleshooting flow chart to resume troubleshooting sequence.
Note
The fault on the preselector can be verified by bypassing the filter to test whether the
Receiver meets its specifications. If it does not, refer to Section 9.5.1.1 on page 9-12 and
retest the Receiver to ensure it meets specifications.
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