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5-5
WARNING: DISCONNECT POWER PRIOR TO SERVICING
C. Second Harmonic Suppressor Adjustment.
D. Neutralization.
5-28.
AM NOISE.
The FM-5T/FM-5TS transmitters are equipped with an
AM NOISE
test re
ceptacle. The test receptacle is located on the transmitter controller and provides a cali
brated AM waveform sample for direct measurement of synchronous and asynchronous
AM noise parameters. Refer to the following text for procedures to minimize AM noise pa
rameters in the transmitter.
5-29.
Synchronous AM Noise.
Synchronous AM noise is incidental amplitude modulation of the
carrier by the presence of FM modulation. The synchronous AM noise level is related to:
1) the transmitter overall bandwidth and 2) transmitter tuning. An application paper
titled TECHNIQUES FOR MEASURING SYNCHRONOUS AM NOISE IN FM TRANS
MITTERS" is available from Broadcast Electronics, Inc. The paper presents detailed infor
mation on AM noise measurements and procedures for tuning the transmitter to minimize
the synchronous AM noise level. If adjustment of the transmitter is desired, perform the
procedures in the application paper and tune the transmitter for a minimum synchronous
AM noise level.
5-30.
Asynchronous AM Noise.
Asynchronous AM noise is residual amplitude modulation of
the transmitter output due primarily to power supply ripple. The transmitter hum null
circuit injects a small 60 Hz voltage into the bias power supply to cancel ac components in
the supply and reduce asynchronous AM noise. Adjustment of the circuit will not normally
be required in the field. However, if it is certain that hum null circuit adjustment is re
quired, proceed as follows.
5-31.
Required Equipment.
The following equipment is required to
adjust the hum null circuit.
A. Distortion analyzer (Tektronics Model AA501 or equivalent).
B. One locally fabricated test cable consisting of the following:
A. 10 feet (3.05 m) of Belden RG58A/U coaxial cable (BE P/N 622-0050).
B. Two BNC connectors (Pomona UG68/U-BE P/N 417-0205).
WARNING
WARNING
NEVER OPEN THE EQUIPMENT UNLESS ALL TRANS
MITTER PRIMARY POWER IS DISCONNECTED. USE
THE GROUNDING STICK PROVIDED TO ENSURE ALL
COMPONENTS AND ALL SURROUNDING COMPO
NENTS ARE DISCHARGED BEFORE ATTEMPTING ANY
MAINTENANCE.
5-32.
Procedure.
To adjust the hum null circuit, proceed as
follows:
5-33.
Refer to Figure 5-2 and connect the distortion analyzer to the controller
AM NOISE
test
receptacle using the coaxial test cable (Item B). Configure the distortion analyzer for dBm
level indications.
5-34.
Operate the transmitter at a normal output power level.
5-35.
Refer to Figure 5-2 and adjust hum null control R10 for a minimum asynchronous AM
noise indication on the distortion analyzer.
5-36.
Disconnect and remove all test equipment.
5-37.
PLATE CURRENT METER CALIBRATION.
The plate current meter assembly is equipped
with a calibration control. Due to the special equipment required to adjust the calibration
control, the control is not considered field adjustable. If it is certain that adjustment of the
plate current meter calibration control is required, contact the Broadcast Electronics Cus
tomer Service Department for maintenance information on the plate current meter assem
bly.
Summary of Contents for FM-5T
Page 1: ...FM 5T FM 5TS 5 KILOWATT FM BROADCAST TRANSMITTERS July 1999 IM No 597 0033 014 ...
Page 14: ...1 3 FIGURE 1 1 FM 5T FM 5TS TRANSMITTER 597 0033 1 COPYRIGHT 1990 BROADCAST ELECTRONICS INC ...
Page 29: ...2 13 COPYRIGHT 1997 BROADCAST ELECTRONICS INC 597 0033 415 FIGURE 2 4 TRANSFORMER TAPS ...
Page 32: ...2 16 597 0033 406 FIGURE 2 6 FM 5T PRIMARY AC WIRING COPYRIGHT 1997 BROADCAST ELECTRONICS INC ...
Page 46: ...3 9 TABLE 3 2 INDICATOR CHECKLIST 597 0098 412 ...
Page 61: ...4 19 FIGURE 4 5 PA CAVITY 597 0032 32 COPYRIGHT 1997 BROADCAST ELECTRONICS INC ...
Page 83: ...5 22 WARNING DISCONNECT POWER PRIOR TO SERVICING BLANK PAGE ...
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