User's Manual

3300-Watt VHF Low Band Transmitter Chapter 2, System Description,
Maintenance & Remote Control Connections
335B, Rev. 0 2-8
Table 2-7. VHF Amplifier Tray Fault Indicators
INDICATOR DESCRIPTION
DS1
Overdrive
Indicates that the level of drive is too high. The protection
circuit will limit the drive level to the set threshold. The fault
is generated on the overdrive protection board.
DS2
Enable
Indicates that the Enable supplied by the exciter tray is
present
DS3
Module Status
Indicates that the forward power sample level is lower than
the set reference level
DS4
VSWR Cutback
Indicates that the reflected level of the tray has increased
above 20%; this will automatically cut back the output power
of the tray. The fault is generated on the AGC control board.
DS5
Overtemperature
Indicates that the temperature of (A4-A5, A4-A6 or A5-A2)
one of the thermal switches is above 175° F. When this fault
occurs, the Enable to the switching power supply is
immediately removed.
Table 2-8. VHF Amplifier Tray Control Adjustments
ADJUSTMENT DESCRIPTION
R2 – A7
Phase
Adjusts the phase of the RF output by approximately 70°.
R3 – A6
Gain
Adjusts the gain of the RF output when the amplifier control
board is in the AGC mode.
Table 2-9. VHF Amplifier Tray Sample
SAMPLE DESCRIPTION
J5
RF Front Panel Sample
Forward power sample of the tray from the AGC control
board.
2.3 Maintenance
The 335B is designed with components
that require little or no periodic
maintenance except for the routine
cleaning of the fans and the openings in
front panels of the trays.
The amount of time between cleanings
depends on the conditions within the
transmitter room. While the electronics
have been designed to function even if
covered with dust, a heavy buildup of
dust, dirt, or insects will affect the
cooling of the components. This could
lead to a thermal shutdown or premature
failure of the affected trays.
When the front panels of the trays
become dust covered, the top covers
should be removed and any accumulated
foreign material should be removed. A
vacuum cleaner, utilizing a small wand-
type attachment, is an excellent way to
suction out the dirt. Alcohol and other
cleaning agents should not be used
unless you are certain that the solvents
will not damage components or the silk-
screened markings on the trays and
boards. Water-based cleaners can be
used, but do not saturate the
components. The fans and heatsinks
should be cleaned of all dust or dirt to
permit the free flow of air for cooling
purposes.
It is recommended that the operating
parameters of the transmitter be
recorded from the meters on the trays at
least once a month. It is suggested that