MFJ-904/904H Deluxe Travel Tuner
Instruction Manual
2
position 10 (fully open). Be sure to use the highest possible capacitance for
each band. This will provide the smoothest tuning, highest efficiency, and
greatest power handling capability.
The INDUCTANCE switch has maximum inductance in position "A", and
minimum inductance in position "L". Less inductance is needed as the
frequency is increased. If too little inductance is used, the tuner may not match
the load properly. If too much inductance is used, the tuner will be "touchy",
power handling will be compromised (capacitors could arc, etc.) and the
bandwidth will not be as wide.
Special Note: Always use the minimum amount of inductance as possible.
Minimum inductance gives the best efficiency, maximum power
handling, and widest bandwidth.
The MFJ-904/904H covers 80 through 10 meters.
Do not operate on 160
meters.
SWR/Wattmeter:
The built-in SWR/Wattmeter measures forward and reflected power and
indicates SWR. The It has 2 power scales which are selected with the front
panel push button switch. The low power scale reads from 0-30 watts forward
and 0-6 watts reflected. The high power scale reads from 0-300 watts forward
and 0-60 watts reflected. SWR is indicated from 1:1 to
∞
.
The MFJ-904/904H has an illuminated meter. To provide power for the meter
lamp, a 12 Vdc supply such as the MFJ-1312D should be used. Use a standard
2.1 mm coaxial plug with the center conductor positive and the sleeve ground.
To measure forward and reflected power press the selector switch to the correct
power setting. Transmit a steady carrier and read the power from the meter.
Each unmarked picket on the scale is an even division between the adjacent
marked values. SWR is read from the SWR curve closest to where the meter
needles cross.
Tuning Procedure:
1. Position the TRANSMITTER control to 5 on the corresponding scale.
2. Position the ANTENNA control to 0 on the corresponding scale.
3. Place the BYPASS/TUNE switch in the TUNE position.
4. Apply just enough power to obtain noticeable deflection on the reflected
power meter or SWR meter.