MFJ-993 IntelliTuner Automatic Antenna Tuner
Instruction Manual
©
2003-2004 MFJ Enterprises, Inc.
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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 non-
volatile memory and reverts back to the default when the tuner power is turned off. Refer to Figure 10 for
the on-screen LC Limit indicator. Default is ON.
WARNING:
LC Limit is a safety precaution; the tuner is in danger of being damaged if this
function is turned off.
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, 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 [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. 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 matching. The reflected needle bouncing to 20-watt mark indicates changing to bypass mode.
Meter Codes and Audible Beeps
In addition to displaying power and SWR, the meter also indicates tuner status. The meter needles
bounce, or rise to one point and stay, to provide information. In this mode the meters do
not
indicate
power levels. For example, when you press [C-DN] and [L-DN] simultaneously to place the tuner in
bypass mode, the reflected needle bounces to the 20 watts mark until you release the buttons. The
following tables show the meter needle stationary and bounce codes.
Summary of Contents for MFJ-993
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