MFJ MFJ-945E User Manual
MFJ-945E Mobile Tuner
MFJ-945E MOBILE TUNER
General Information:
The MFJ-945E Mobile Tuner is a compact tuner designed for m obile operation in cars, trucks,
RV's, and boats. Covering
mobile whip antenna. It will also match almost any antenna for hom e station operation such as
dipoles, inverted-vees, verticals, beam s , random wires, and other s fed by coax lines or single wire.
The MFJ-945E employs a cross-needle m eter so forward power, reflected power, and SWR may
be read simultaneous ly. T he meter lamp can be powered by a 12Vdc, 300mA s our ce, s uc h as the
MFJ-1312B for hom e-station operation. The meter lamp
lamp. Use a 2.1mm coax ial plug with the center conductor of the plug connected to the positive
and the sleeve connected to ground. Optional mobile mounting bracket (MFJ-20) is available.
Cross-Needle SWR/Wattmeter:
The MFJ-945E utilizes a cross-needle meter to read FORWARD power, REFLECTED power and
SWR simultaneously in either HI (300 Watts) or LO (30 Watts) power ranges. Set the power
range switch to HI or LO. Next read the FORWARD power on the Forward Scale. REFLECTED
power is shown at the same time on the Reflected Scale. SWR is read by observing where the two
needles cross. No SWR sensitivity adjustment needed to read SWR. The HI range is
FORWARD and 60 Watts REFLECTED. The LO range is 30 Watts FORWARD and 6 Watts
REFLECTED. The MFJ-945E is factory calibrated on the LO scale at 10Watts FORWARD and
Watts REFLECTED, and on the HI scale at
2
1.8
to
30 MHz
, it will match virtually any transmitter to almost any
ON/OFF
Watts FORWARD and 20Watts REFLECTED.
100
switch will activate the meter
Watts
300
Installation:
Place the tuner in a convenient location at the operating position. Avoid placing the tuner
1.
near microphones, speech processors, TNC's or other RF sensitive devices.
Install the MFJ-945E between your transmitter and antenna. Connect a coax line from your
2.
transmitter to the SO-239 connec tor labeled
Connect your antenna to the SO-239 connector labeled
tuner. A random wire antenna may be connected to the center connec tion of the
connector. The random length wire should be long, high, and as clear of surrounding
objects as possible! For optimum operation, the wire antenna should be a
or longer at the operating frequency. Do
the tuner is well grounded to the transmitter! A post labeled
ground connection(s).
NOTE:
If random wire operation is desired, position the tuner so that the rear panel terminals
can not be contacted by persons or conductors! W hen transmitting with random wire,
the rear panel connectors can operate with high RF voltages. These voltages may
cause serious burns and may also damage anything contacting or within 1/2" of the
terminals!
TRANSMITTER
ground the random wire antenna. Ensure that
not
on the rear panel of the tuner.
ANTENNA
on the rear panel of the
ANTENNA
1/4-wavelength
GROUND
is provided for
1
MFJ-945E Mobile Tuner
MFJ-945E Front Panel
Using the MFJ-945E:
The
INDUCTOR
minimum inductance at position L. Less inductanc e is needed at higher f requencies than at low
frequencies for the same impedance. The
represent maximum capacitance at position 10. For optimum operation of the MFJ-945E, the
transmitter must be tuned to a 50 Ohm output impedance at the operating frequency.
tune the transmitter at a low output power!
setting after loading it to a 50 Ohm load! After properly tuning the transmitter, tune the MFJ-945E
for a minimum SWR as described below:
NOTE
:
1.
When using the MFJ-945E for receiving only, tune as described in Steps 1 and 2.
Set the
opened at this setting.
Rotate the
2.
receiving mode.
WARNING:
While transmitting a steady state carrier (CW), alternately adjust the
3.
TRANSMITTER
controls can best be adjusted by turning the
time, then rotating the
minimum SWR is obtained.
If an SW R of
4.
Step 3. If arcing should occur between the capacitor plates, increase or decrease the
INDUCTOR
repeat Step 3 for each
switch on the MFJ-945E represents maximum inductance at position A and a
TRANSMITTER
INDUCTOR
and
ANTENNA
and
ANTENNA
TRANSMITTER
Do
readjust the transmitter loading control
not
controls to position 5. The tuning capacitors are half
control until maxim um noise is obtained with your tranceiver in the
controls both
Never transmit while changing the INDUCTOR setting!
ANTENNA
controls for minimum SW R. Since both of these c ontrols interact, the two
TRANSMITTER
ANTENNA
is not obtained, increase or decrease the
1:1
control for m inimum SWR. Repeat this procedure until
control one position, then repeat Step 3.
INDUCTOR
control position.
NOTE:
control a sm all increment at a
INDUCTOR
If you can't obtain a
control and repeat
1:1
Always
and
SWR,
2
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