Specifications

b. Press the VSWR TEST pushbutton on the Control front
panel. The VSWR TEST LED on the panel should turn
RED for 5 seconds and then return to GREEN.
c. If it does not change or remains RED, the VSWR test
circuit is not operating correctly and the transmitter
should not be operated until the problem is resolved.
6.4.9
Output Monitor Antenna VSWR
6.4.9.1 Multiple VSWR Conditions
If the transmitter is operating at reduced power or has shut itself
off, and the OUTPUT MONITOR ANTENNA VSWR/ANA-
LOG INPUT POWER FOLDBACK Control front panel LEDs
are illuminated RED, then more than five VSWR events have
occurred within twenty seconds. If enough successive VSWR
conditions have occurred, the transmitter will foldback in power
and eventually shut off.
6.4.9.2 Single VSWR
a. If only the OUTPUT MONITOR ANTENNA VSWR
Control panel LED is illuminated RED and the transmitter
is still at the normal power, less than five VSWR events
have occurred within twenty seconds.
b. The ANT NULL position on the front panel will normally
be 0 on the meter if the transmitter is properly tuned into
the antenna. Any antenna VSWR will show up as an
upscale meter deflection.
6.4.9.3 Clear The Fault
a. The first step is to clear the fault by pressing the RESET
switch on the Control front panel.
1. If the fault clears, the transmitter should return to the
normal power level and the OUTPUT MONITOR
NETWORK LED should return to GREEN. If this
occurs, then a VSWR fault is no longer present but
should be monitored in the future.
6.4.9.4 Fault Will Not Clear
a. If the fault remains RED, the source of the VSWR fault
must be repaired before full power operation cancontinue.
Some possible causes of antenna VSWR are:
a. ARCING
1. Static discharge or discharge due to lightning across
ball gaps, guy wire insulators, or possibly across com-
ponents already operating close to their voltageratings.
2. Static charge buildup can occur on towers that do not
have provision made for static discharge, such as static
drain chokes.
3. Static charge buildup can occur during under condi-
tions of rain, snow, or even blowing dust or sand.
4. Dirt build up or moisture (including condensation) on
insulating surfaces and inside a transmission line can
cause the voltage breakdown rating to be reduced. This
can occur if pressurized gas filled lines lose pressure
or if the dehydrator in the line pressurization unit fails.
5. In new systems, insufficient voltage rating of compo-
nents, such as capacitors, insulators, or spark gaps may
be set too close.
b. TRANSIENT signal pickup may occur during thunder-
storms, even from distant lightning strikes in some cases.
Lightning strokes may induce currents in towers, causing
currents on the transmission lines that can reach the phase
detectors and give a VSWR overload indication.
c. INTERFERENCE: Other nearby stations’signals can also
induce voltages and currents in antenna systems that are
large enough to be detected by the phase detector and
cause VSWR overloads. The solution in such cases may
be a trap or filter in the antenna impedance matching
network or phaser.
d. LOAD IMPEDANCE CHANGES - The Reflected Power
reading and Antenna Null position on the front panel
multimeter is the best indication of the antenna operating
impedance once initially tuned into the antenna. If the
Reflected Power and Antenna null indications change this
indicates an impedance change of the transmitter load.
The load impedance should be checked with proper im-
pedance measuring equipment, and the improper load
should be corrected if possible.
It is possible for the network VSWR detector to be at fault.
6.4.9.5 Testing the Antenna VSWR Detector:
a. Turn on the transmitter and apply an RF Mute by selecting
the RF MUTE position with S1 on the Controller.
b. This keeps the power in the output network to 0W and
therefore no actual VSWR should be generated.
c. Press the VSWR TEST pushbutton on the Control panel.
The VSWR TEST LED on the panel should turn RED for
4 seconds and then return to GREEN.
d. If it remains RED, the VSWR test circuit is not operating
correctly and the transmitter should not be operated until
the problem is resolved.
6.4.10
VSWR Test
The VSWR TEST LED is an indicator that the transmitter is
performing a VSWR TEST, a VSWR fault or ARC has just
occurred, or that the VSWR detector has failed. When the
transmitter is first turned on or when a different power level is
selected, thisLED should illuminate RED for 4 seconds and then
return to GREEN. If during normal operation, the LED is
illuminated RED and does not return to green within 4 seconds,
the VSWR circuits may have failed and should be tested to
determine if they are operating properly.
Note
Pressing the front panel reset has no effect on this indicator.
This LED can only be reset by a successful completion of the
VSWR test. If the LED remains RED after 4 seconds, trou-
bleshoot the VSWR TEST circuit.
a. If the VSWR TEST pushbutton is pressed while S21 is
depressed and held down on the Output Monitor, the
VSWR TEST LED should remain RED. If this occurs, the
VSWR TEST circuit (which is Inhibited by S21) will not
have detected a VSWR and should remain illuminated
RED indicating that the circuit failed the test. This is a
888-2339-002 6-7
WARNING: Disconnect primary power prior to servicing.