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VSWR exceeds 1.8 to 1. This will stress the output
stage and could destroy the RF transistors; this type of
misuse and failure is not covered under warranty.
Measure the VSWR at the center of the operating band.
Tune the antenna (according to the manufacturer’s
tuning instructions) so that the VSWR is as close to
1.1 to 1 at the center of the operating band.
Next, measure the VSWR at the lowest and highest
frequency of the transceiver. If the antenna has a wide
enough frequency range and band-pass, the VSWR
readings should be below 1.5 to 1 across the entire
operating band. If at the lower or upper end of the trans-
ceiver operating frequency, the VSWR measures more
than 1.5 to 1, it is recommended that the antenna be
re-tuned before operating on those frequencies.
If you are experiencing unusual VSWR readings check
for the following possible problems:
1) Make sure that the antenna is installed properly and
grounded.
2) Check all coaxial cable and connectors for defects
and poor routing.
3) If testing a vehicle installation, make sure that all
vehicle doors are closed when testing.
4) Do not test near or around large metal objects or
buildings.
7.
Ignition Noise
In certain vehicle installations, electrical noise or inter-
ference may be present in the receive audio of the trans-
ceiver. Typically the vehicle’s ignition system or more
specifically the alternator generates this noise. The
Magnum 257 is equipped with a noise blanker circuit
that is designed to improve, and in many instances
eliminate, this electrical noise.
In extreme cases, the noise blanker may not eliminate
all the electrical noise. In such cases, an after-market
alternator noise or ignition noise filter can be purchased
and installed according to the manufacturer’s instruc-
tions. If purchasing an alternator noise filter for the
Magnum 257 make sure the filter is rated for at least
10 amps continuous current draw.
