MFJ-998RT Legal Limit IntelliTuner
TM
Automatic Remote Antenna Tuner Instruction Manual
© 2011 MFJ Enterprises, Inc
MFJ-998RT Version 1A
15
Radio Interface Menu
This function is not used in the Remote Tuner. Leave this setting OFF.
Auto/Semi-Automatic Mode
Semi-automatic operation is not available on the remote tuner. Leave in AUTOMATIC mode.
Pressing [TUNE] and [ANT] simultaneously toggles between automatic or semi-automatic tuning mode. In
automatic mode, the tuning routine is automatically started when at least five watts of power is applied
and the SWR is a preset amount above the preset target SWR. The Auto/Semi indicator on the main
display indicates the selected mode.
LC Limit Menu
The upper limits of inductance (L) and capacitance (C) are factory-limited according to frequency and
maximum power rating; i.e., higher frequencies need less inductance and less capacitance when the
Lnetwork is properly tuned. Pressing [C-UP] and/or [L-UP] allows capacitance and inductance to be
increased only to these limits. When a selected capacitance or inductance is higher than its allowed limit,
and the frequency is changed, that selection is automatically reduced to the value of its limit. These limits
are used to prevent matching of extreme load impedance outside the tuner’s specification, which may
result in excess voltage and/or current across the tuner’s components. This setting is not stored in
nonvolatile memory and reverts back to the default when the tuner power is cycled. Refer to Figures 6
and 7 for the on-screen LC Limit indicator. If this feature is turned OFF, it will be re-set to ON whenever
power is cycled. Default is ON.
WARNING:
LC Limit is a safety precaution; the tuner is in danger of being damaged if this function is turned off.
Setup Operation
Manual Tuning
Note: Manual tuning must only be attempted under low power (less than 20 watts) conditions.
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. Changing frequencies may
raise the SWR but still be within the SWR retune window. Manual tuning gives the user control of the
tuner if desired, and the L-Network menu provides a picture of the matching network configuration.
Manual tuning is accomplished by using the [C-UP], [C-DN], [L-UP], and [LDN] 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. The L-Network menu displays the capacitance on the left to indicate that
the capacitance is on the antenna side (corresponding with the rear panel configuration of connectors);
the capacitance value moves to the right side of the display when the capacitance is on the transmitter
side of the inductance. A general rule of thumb is that loads with impedance higher than 50 ohms call for
the capacitance on the antenna side; loads with impedance lower than 50 ohms call for the capacitance
on the transmitter side.
Pressing [C-DN] and [L-DN] simultaneously or pressing [TUNE] quickly places the tuner in bypass mode;
i.e. zero inductance and zero capacitance. RF from the transmitter goes directly to the antenna with no
