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User's Manual | ACOM 04AT | Remote Automatic Antenna Tuner and Switch
7.4. Troubleshooting - Monitoring the Antenna-feeder Path Status
Using the ATU MEASURE function, you can evaluate the status of the antenna-feeder path and the coaxial
cable from the amplifier to the tuner.
a)
We recommend that you access the ATU MEASURE menu, and check the SWR of the antenna
output there, while you are sure of the good working condition of the antennas and feeders.
Run this measurement for both the operating frequencies and at least one non-operating
frequency, where SWR should be poor (if the tuner cannot be tuned to this frequency, use
BYPASS mode during measurements). Copy and store the data for your antennas and then use
it as a reference in diagnostics;
b)
When running diagnostics, use the ATU MEASURE menu to check SWR at the antenna output
at a frequency for which you know that the antenna SWR should be poor (if the tuner cannot
be tuned to this frequency, use BYPASS mode). If you measure a good instead of poor SWR at
the antenna output, this indicates high losses in the feeder from the antenna output to the
antenna or in the antenna itself. If SWR in the ATU MEASURE menu is really poor (as it was
earlier), go to the tuner's BYPASS mode and measure the SWR at the input of the coaxial cable
in the radio station: if it is also poor and if the SWR to the amplifier becomes good after a
tuning, then the cable to the radio station is with low losses;
If SWR at the antenna output (in the ATU MEASURE menu) is poor, but bypassing the tuner it
becomes better at the input to the radio station, then probably the losses at the cable from
the radio station to the tuner are high. E.g., there may be moisture in the braid, the dielectric
may be soaked with water (if it isn't solid), or the braid may be corroded. Such coaxial cable
should be replaced with a new one, because it will introduce high losses and impedance
instability in both transmission and reception, and could also induce interference at reception;
c)
If after tuning the tuner shows that it has achieved a good SWR, but you find poor SWR at the
amplifier end (e.g., by the SWR indicator of the transceiver or amplifier), this shows that the
feeder from the radio station to the tuner may be unsuitable or faulty (the cable impedance
may differ from 50 Ohm, or there is a poor contact or leakage at some connector);
d)
If you receive a TIMEOUT EXPIRED message while trying to tune the unit (even when the tuning
power is increased to 50 W) and, at the same time, SWR at the bottom end of the feeder (in
the radio station) is good during tuning, this means that:
-
The losses at the feeder may be so high that out of the 50 W fed, under 12 W reach the
remote unit, which is not enough to tune the tuner;
-
There may be a blown fuse F2 at the tuner (see Section
e)
If you receive a TIMEOUT EXPIRED or UNSTABLE RF POWER message while trying to tune the
unit (even when the tuning power is increased to 50 W) and, at the same time, SWR at the
bottom end of the feeder (in the radio station) is much higher than 2:1 during tuning, this
means that:
-
The cable impedance from the radio station to the remote unit may be other than
50 Ohm or may be faulty or disconnected;
-
The transceiver power may be modulated or unstable (it should be unmodulated
carrier); check for loose or contaminated connectors;
-
There may be a blown fuse F1 at the tuner (see Section
May 2021
7.2 Fuse Replacement
7.2 Fuse Replacement
S e c t i o n MAINTENANCE | Page 59 of 72
);
);
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