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MFJ-991 / MFJ-994 IntelliTuner Automatic Antenna Tuners
Instruction Manual
Meter Range
Note: All meter power readings and ranges are ×2 in the model MFJ-994.
You can select a meter scale range or use auto range. In the 30 watts (low) range, the forward full scale is
30 watts and the reflected full scale is 6 watts (divide the meter reading by 10). In the 300 watts (high)
range, the forward full scale is 300 watts and the reflected full scale is 60 watts. Auto range automatically
sets the meter scales according to the input RF power to the tuner. Forward power greater than 30 watts
or reflected power greater than six watts automatically sets the meter to the high power range. Forward
power less than 25 watts and reflected power less than four watts automatically set the meter to the low
power range. Default is 300 watts range.
Press [TUNE] and [C-DN] simultaneously to toggle Auto Range on and off. Press [TUNE] and [L-DN]
simultaneously to toggle between 300 and 30 watts meter range and disable Auto Range.
Operation
Manual Tuning
In certain cases the operator may wish to "touch up" the tuner's settings. For example, if the target SWR
is set at the default of 1.5, the tuner will stop when a match of 1.5 is found. In all cases, manual tuning
gives the user control of the tuner if desired. Manual tuning is accomplished by using the [C-UP], [C-
DN], [L-UP], and [L-DN] buttons. Since it is not known if more or less capacitance (or inductance) is
needed, manual tuning must be by trial-and-error. Press [C-UP] one time, and the reflected power will
indicate if [C-UP] was the right "direction." If it was, press [C-UP] again and observe reflected power. If
not, press [C-DN] twice (once to return to the original setting of C, and once for one click past it).
Manual tuning of inductance is similarly accomplished, using [L-UP] and [L-DN]. Since the capacitance
and inductance are interdependent, some back-and-forth between the two may be needed, just as in a
conventional tuner with knobs. Once you are familiar with this process, you will learn how to match
certain antennas and frequencies.
Pressing [C-UP] and [C-DN] buttons simultaneously moves the capacitance back and forth from one side
of the inductance to the other. Factory default is with the capacitance on the transmitter side. To move
the capacitance to the opposite (antenna) side, press [C-UP] and [C-DN] simultaneously. The reflected
needle will bounce to 5 watts. Press [C-UP] and [C-DN] simultaneously again to return the capacitance
to the transmitter side (and the forward needle will bounce to 30 watts to indicate the change). A general
rule of thumb is that loads with impedance higher than 50 ohms call for the capacitance on the antenna
side; loads lower than 50 ohms call for the capacitance on the transmitter side.
Pressing [C-DN] and [L-DN] simultaneously places the tuner in bypass mode; i.e. zero inductance and
zero capacitance. RF from the transmitter goes directly to the antenna with no matching. The reflected
needle bouncing to 20-watt mark indicates changing to bypass mode.
© 2004 MFJ Enterprises, Inc.
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