TROUBLESHOOTING AND REPAIR
RF LEVEL/AM
Output PCA Het Mixer Level Adjustment, R72 6D-18.
TEST EQUIPMENT:
• Power meter
• Power sensor (High-Level)
• Spectrum analyzer
REMARKS:
The UUT must be operated at room temperature for at least one hour with the module
covers in place before continuing with this adjustment procedure.
This adjustment is normally required only when mixer U4 or het band LO circuitry is
replaced. When adjusted, an interaction with R10 exists, therefore R10 adjustment is
included in this procedure.
CAUTION
This adjustment directly affects the output level and should not be made
indiscriminately.
PROCEDURE:
With the UUT programmed to +16 dBm and 14.9 MHz, the worst in band spur is
adjusted to be well within specification. A lower level of this spur degrades the
broadband noise in the het band. The het level is then appropriately readjusted.
1. Remove bottom cover and appropriate access screws on bottom module plate for
R10 and
R72.
2. Program UUT to SPCL 01, 15 MHz, and +16 dBm. Connect the power meter to
the output of the UUT. Edit the level to +16 dBm. Set the power meter to dB(ref).
3. Edit the frequency to 14.9 MHz and adjust R10 for 0 dB(REL)
4. Connect the spectrum analyzer to the UUT and observe the spur at 5.5 MHz. This
spur should be observed with high spectrum analyzer attenuation (typically 30 dB)
to avoid internal analyzer spurs. The resolution bandwidth and span should be
narrow (typically a span of 1 kHz and resolution bandwidth of 10 Hz) to allow the
spur to be seen clearly.
5. Adjust the spur to a level of -89 dBm ±2 dB with R72. This has changed the
adjustment in step 3 above so steps 3 through 5 must be sequenced again until level
is 0 dB(REL)±.l dB.
6. Reinstall the access screws.
6D-16
To Next Page
Loading...
