User Manual

Maintenance RF-Orchestra!™ Transmitter Installation and Operation
6-16 6880493G02-C July 2000
Check Power at Internal and External Wattmeters
Read the power output via RFO FIPS: a79x, a80,ora 192 SPCQ 64.The internal and external
wattmeters are calibrated in the factory and provide for an easy way to accurately measure the
power. See Chapter 5, “Operation”, for a procedure to check out the wattmeters.
• High External Reflected Power
Reflected power should be below 2 watts. Check for bad connections or water in the
antenna and connectors. A Frequency Domain Reflectometer may be used to find the
location of the mismatch. Return loss should be less than 14 dB at the operating
frequency.
• Low Power Output at the Antenna, High Internal Reflected Power
For 75 Watts at the internal meter it is typical to output about 55 watts at the external
meter. Check the insertion loss of the cavity filter, which can be tuned. Typical insertion
loss should be 0.8 to 1.2 dB. An improperly tuned cavity filter will result in high reflected
power and a poor spectral output.
• Power Not Set Correctly or Defective Power Detector
Check the power at the couplers with a commercial power meter to verify that the
built-in detectors are accurate. If not within 5%, calibrate wattmeters and align power
output.
• RF Signal Path
Check the feedback path to the exciter. If the feedback to the exciter is disconnected or
there is a reflection, the PA may be unstable producing a high power wideband signal.
The carrier (normally suppressed) will be too high. Check to make sure the exciter is
properly inserted. Defective couplers can also cause this problem. Typically, if this
problem exists, the transmitter will shutdown due to FM Clipping.