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INSTALLATION
1.
Contents
Unpack and inspect your Magnum 257 for missing or
damaged components. Your 257 includes the follow-
ing items:
Quantity
Description
1
Magnum 257 Transceiver
1
Microphone with Up/Down Controls
1
Mounting Bracket with Hardware
1
Microphone Hanger with Hardware Set
1
Operating Manual with Schematic
2.
Microphone Hanger
The microphone hanger may be attached to the side
of the transceiver, or any other convenient location. Use
the provided screws to attach the microphone hanger
either vertically or horizontally to the side of the trans-
ceiver.
3.
Mounting
When attaching the 257 mounting bracket to the ve-
hicle, choose a location that will provide easy access
to all front panel controls and air circulation to the rear
panel. When selecting a mounting location, make sure
that there is ample space behind the control deck for
the cables. Do not pinch, or bend sharply, the power or
antenna cables. Do not install the 257 in any compart-
ment that restricts airflow and do not install in a loca-
tion that interferes with the safe operation of the ve-
hicle.
Attach the mounting bracket to the vehicle first then
mount the 257 to the bracket. If the rear panel is not
accessible you may want to attach the power and an-
tenna cable prior to mounting.
4.
Electrical Connections
The Magnum 257 is designed to work on any 13.8 volt
DC, negative ground, source. The condition of a
vehicle’s electrical system can affect operation. A low
battery, worn generator/alternator, or poor voltage regu-
lator will seriously impair the performance of the trans-
ceiver. Any of the above conditions could result in a
high level of receiver noise generation or a substantial
loss of the transmitter’s RF output. Make sure that all
of these components of your vehicle’s electrical sys-
tem are in good condition prior to installing the trans-
ceiver.
CAUTION!
VOLTAGE EXCEEDING 15 VDC WILL DAMAGE
THE RADIO. MEASURE VOLTAGE AT BATTERY
TERMINALS, WITH VEHICLE RUNNING, PRIOR
TO INSTALLATION!
Before making any electrical connections make sure
the AF gain (volume) control on the control deck is in
the “OFF” position.
Connect the positive (+) red wire of the DC power cord
to a positive 13.8 volt source at the vehicle fuse block.
If connecting to the fuse block, it is recommended that
a switched power source is used so that the power to
the transceiver is disconnected when the vehicle is off.
This will eliminate the possibility of the transceiver drain-
ing the vehicle’s battery.
Connect the negative (-) black wire to a metal part of
the vehicle’s frame, or chassis ground. Make sure that
this is a good ground connection.
The 257 power cord may also be connected directly to
the battery. Connecting directly to the battery has sev-
eral benefits, the first of which is to maximize RF out-
put. Secondly, the battery is a very large capacitor and
will help eliminate certain types of ambient and vehicle
noise. If connecting directly to the vehicle’s battery, ad-
ditional power cable may be required. On runs of 8
feet or less use 14-gauge stranded wire. Use 12-gauge
wire on longer runs.
5.
Antenna Connection
The transceiver will operate using any standard 50-
ohm ground-plane, vertical, mobile whip, long wire or
similar antenna. The antenna should be rated at 50
watts PEP minimum. A standard SO-239 type antenna
connector is located on the rear panel of the 257. Con-
nection is made using a PL-259 and high grade co-
axial cable (RG213, RG58A/U or Mini RG-8 is recom-
mended).
A ground-plane antenna provides greater coverage and
is recommended for fixed station-to-mobile operation.
For point-to-point fixed station operation, a directional
beam antenna operates at greater distances even un-
der adverse conditions. A non-directional antenna
should be used in a mobile installation; a vertical whip
is best suited for this purpose. The base loaded whip
antenna normally provides effective communications.
For greater range and more reliable operation, a full
quarter wave whip may be used. Either of these an-
tennas uses the metal vehicle body as a ground plane.
Once the antenna is mounted on the vehicle, route the
coaxial cable so that it is not next to any power cables
or vehicle cables. Connect the PL-259 to the antenna
connector on the rear panel of the 257. Make sure that
the cables does not interfere with the safe operation of
the vehicle.
6.
VSWR
Before use, it is important to determine the antenna
system’s VSWR (voltage standing wave ratio). First,
make sure the SWR bridge (meter) is in good working
order and is calibrated. To ensure your radio is per-
forming properly the VSWR should never exceed 1.5
to 1. Never transmit on any antenna system where the
