RESPONDING TO ALARMS VX150 TO VX2 TROUBLESHOOTING MANUAL
PAGE 3.1.32 VERSION 2.0 2023-04-20
SWR Foldback The Reflected Power meter measured value is
greater than the foldback threshold. By
default, the models have the following
thresholds:
VX150=6W, VX300=12W, VX600=24W,
VX1=40W, VX1.5=60W, VX2=80W.
The default thresholds are based on the
absolute reflected power equivalent to a 1.5:1
SWR at nameplate power. This threshold can
be adjusted between 1.1 and 1.5:1 SWR in the
transmitter settings page of the Front Panel
User Interface.
This alarm will cause a Foldback to occur,
reducing the amount of forward power out to
maintain reflected power at the foldback
threshold.
The reflected power meter measured value is
less than the foldback threshold, and the
transmitter is no longer limiting forward
power.
This alarm is most likely caused by an
issue in the output transmission line or
antenna system. Antenna Icing
particularly can often cause foldback to
occur as SWR slowly rises due to ice
building on the antenna.
Check for faults in transmission line or
the antenna system, measure load SWR
at the transmitter output.
Be cautious when adjusting the SWR
foldback threshold, as directivity error is
pronounced when measuring reflected
power at low SWR and may cause pre-
mature foldback.
SWR Shutback The instantaneous reflected power has quickly
exceeded the shutback threshold. This will
cause an immediate inhibit of the RF output
to protect the RF PA(s).
The Shutback threshold is based on the
reflected power equivalent to a 2:1 SWR at
the transmitter models nameplate power. (Ex.
VX2=222W).
This alarm will automatically clear
immediately after the transmitter is inhibited.
After clearing, the transmitter will attempt to
resume operation at the active preset output
power. Subsequent Shutbacks may trigger
cutback.
This alarm is most likely caused by an
issue in the output transmission line or
antenna system. Shutback specifically
responds to fast increases in reflected
power caused by open/short circuits,
lightning strikes, or arcs.
Check for faults in transmission line or
the antenna system, looking out
particularly for any evidence of arcing.
Alarm Name Trigger Conditions Clear Conditions Troubleshooting
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