MFJ MFJ-249 - Adjusting Tuners

MFJ-249 SWR Analyzer Instruction Manual
For example, assume an operating frequency of 28 MHz. You want to know what the feedline
loss is at 28 MHz. At that frequency the "SWR" meters need's is in the red uncalibrated
portion of the meter. Increase the measured frequency until the needle falls on a calibration
mark. At 60MHZ the meter reads 3:1 SWR. Using the chart you know that the loss is 3 dB.
Since 28MHz is about half of 6OMHz, you can multiply 3dB by .7 which gives a loss of about
2dB at 283MHz.
ADJUSTING TUNERS
The MFJ-249 can be used to adjust tuners. Connect the MFJ-249 "ANTENNA" connector to
the tuner's 50 ohm input and the desired antenna to the normal tuner output. This connection
can be made with a manual RF switch to facilitate rapid changeover.
Warning: Always connect the common (rotary contact) of the switch to the tuner. The
switch must connect either the MFJ-249 or the stat'on equipment to the tuner.
The Station Equipment Must Never Be Connected Ta The MF J-249.
1 Connect the MFJ-249 to the tuner input.
2 Turn on the MFJ-249 and adjust it to the desired frequency.
3 Adjust the tuner until the SWR becomes unity (1:1).
4 Turn off the MFJ-249 and re-connect the transmitter.
ADJUSTING AMPLIFIER MATCHING NETWOR<S
The MFJ-249 can be used to test and adjust RF amplifiers or other matching networks without
applying operating voltages.
The tubes and other components should be left in position amd connected so that stray
capacitance is unchanged. A non-inductive resistor that equals the approximate driving
impedance of the tube 1s installed between the cathode of the tube and the chassis, or a resistor
should be connected between the anode and the chassis that equals the calculated plate
impedance of the tube . The appropriate network can now be aqjv ited.
The antenna relay (if internal) can be engaged with a small power supply so that the coax input
and output connectors are tied to the networks.
Caution: The driving impedance of most amplifiers changes as the drive level is varied. Do
not attempt to adjust the input network with the tube in an operating condition
with the low level of RF from the MFJ-249.
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