MFJ MFJ-924 User manual

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MFJ-924440 MHz UHF ANTENNA TUNER
Thank you for purchasing the MFJ-924 440 MHz UHF Antenna
Tuner. It will handle up to 300 watts PEP of output power. It
is designed to match a wide range of impedances for coax fed
antennas. SWR/WATT meter is built-in.
INSTALLATION
1. Connect your coax line fed antenna to the coax connector on
the MFJ-924 marked ANTENNA.
2. Connect a short coax line from the coax connector on the
MFJ-924 marked TRANSMITTER to the antenna connector of
your transceiver.
3. Connect a ground wire from the GROUND wing nut of the
MFJ-924 to the transceiver ground or earth ground of
your station.
OPERATION
SWR/WATT Meter
1. SWR Measurement:
a. Set the push button switch to SET posit/ n (TN).
b. Transmit a continuous carrier and set the SWR/POWER
control for a full scale meter deflection.
c Set the push button switch to SWR position (OUT) and
2. Power Measurement:
a. Set the push bottom switch to SET position (IN).
b. For 30 watts range -- rotate the SWR/POWER control to
the 30 the and read the power level on the 30
watt scale.
c. For 300 watts range range -- rotate the SWR/POWER
control to the 300 mark and read the power level on
the 300 scale.
Note:The SWR/POWER control on the MFJ-924 is factory
calibrated for the 30 watts range. Do not reset the
knob on this control. However, due to component
tolerance when precision reading is desired, the 300
watt range can be re-calibrated as follows:
a. Set the push button switch to SET position (IN).
b. Rotate the SWR/POWER control to the 30 mark and read
the power level on the 30 watt scale.

c. Rotate the SWR/POWER control counter-clockwise until
the power level reading on the 300 watts scale is the
same as it is on the 30 watts scale as note on Step b.
above.
d. Mark the control setting for the re-calibrated 300 watt
range.
Antenna Tuner Operation
The ANTENNA and TRANSMITTER controls on the MFJ-924 present a
minimum capacitance at "0" and a maximum capacitance at "10".
After properly installing the MFJ-924, use the tuner to tune
for minimum SWR as describe below.
1. Set both the TRANSMITTER and ANTENNA controls to "0".
2. Apply enough transmitter power to have an adequate
indication on your SWR meter. Do not apply full power while
tuning for minimum SWR.
3. While transmitting, alternately adjust the TRANSMITTER
control and the ANTENNA control for minimum SWR. Since the
TRANSMITTER and the ANTENNA controls interact, the two
controls can best be adjusted by turning the TRANSMITTER
control at a small increment at a time and then rotating
the ANTENNA control for the minimum SWR. Repeat this
process until a minimum SWR is obtained.
4. After minimum SWR is obtained, full output power up to
300 watts PEP may be applied to the MFJ-924.