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6. VSWR
Before use, it is important to determine the antenna
system’s VSWR (voltage standing wave ratio). You will
need a high quality SWR bridge (meter) to accurately
tune your antenna system. First, make sure the SWR
bridge is in good working order and is calibrated. To
ensure your radio is performing properly the VSWR
should never exceed 1.5 to 1. Never transmit on any
antenna system where the 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 antenna
manufacturer’s tuning instructions) so that the VSWR
is as close to 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 S-9 is equipped with a noise blanker circuit
that is designed to reduce, and in many instances elimi-
nate, this electrical noise.
In extreme cases, the noise blanker may not eliminate
all the electrical noise. In such cases, an alternator/
ignition noise filter can be used. The PLF-10C FilterCord
by Magnum International is designed for use with the
Magnum S-9 and is an effective way to eliminate alter-
nator and ignition noise problems.
