TROUBLESHOOTING AND REPAIR
RF LEVEL/AM
11. Use the EDIT knob to program the UUT to +17 dBm. Note the power meter
reading.
12. Use the EDIT knob to program the UUT for +2 dBm. Verify that the power meter
reading is 15 dB ±0.2 dB below the previous reading.
13. Program the UUT for SPCL 50. This disables amplitude fixed range.
14. Disconnect the power sensor from the UUT, and replace the detector offset
adjustment access screw.
Mod Control PCA AM Depth Adjustment, R10 6D-14.
TEST EQUIPMENT:
•
DVM
• Modulation Analyzer
• Low-Frequency Synthesized Signal Generator (LFSSG)
REMARKS:
The UUT must be operated at room temperature for at least one hour with the module
plate covers in place before continuing with this adjustment procedure.
CAUTION
The AM depth adjustment directly affects the output level and should not be
made indiscriminately.
The AM depth adjustment is normally required only when components in the AM
signal processing circuits have been replaced. If this adjustment is made, it is then
necessary to repeat 6D-13 (Detector Offset Adjustment, R28) and perform the RF
Level Adjustment, R20.
PROCEDURE:
Adjust the AM depth adjustment, R10, for 90% AM depth as measured with the
Modulation Analyzer when the UUT is programmed to 90% AM.
1. Remove the AM depth adjustment access screw from the bottom module plate
cover.
2. Connect the output of the LFSSG to the UUT MOD IN connector and to the
DVM using a BNC Tee.
3. Program the UUT to SPCL 01, 350 MHz, +4 dBm, and EXT AM AT 90% AM
DEPTH.
4. Program the LFSSG for 1 KHz and a voltage of 0.7071 RMS as measured by the
DVM.
5. Connect the UUT RF OUTPUT connector to the modulation analyzer input.
6. Program the modulation analyzer to measure AM + Peak, in a 0.05- to 15-kHz
bandwidth.
6D-13
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