MFJ MFJ-5124K Instruction Manual download pdf (Page 24)

MFJ-993B IntelliTuner Automatic Antenna Tuner Instruction Manual

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 L-

network 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 non-

volatile memory and reverts back to the default when the tuner power is turned off. Refer to Figures 11

and 12 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.

Also, the decimal point in the SWR reading is replaced with a comma.

Pressing [TUNE], [C-DN] and [L-DN] simultaneously overwrites the tuner memory with the current

tuner setting; settings with SWR greater than 3.0 will not be stored. Both forward and reflected needles

go to full scale and one beep indicate memory overwrite.

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MFJ MFJ-5124K Instruction Manual Page 24