MFJ MFJ-976 - Operation of the MFJ-976 Tuner

MFJ-976 Legal Limit Fully Balanced Antenna Tuner Instruction Manual
5
+
POWER
12VDC
GROUND
TRANSMITTER
RANDOM WIRE
BALANCED LINE
ANTENNA
Connect the jumpers across
the terminals to the right for
unbalanced operation. The
broken lines indicate the
jumper connections
Operation
The roller inductor has maximum inductance at about 000 and minimum inductance at 125 on the
reference counter. The capacitors have maximum capacitance at 0 and minimum capacitance at 10. In
simple language, as the frequency is increased, the normal control positions rotate clockwise just like on
other equipment.
Note: Always use the most capacitance (settings closest to 0) for the most power handling and the least
loss. Use the smallest possible inductance (the lowest number possible) also.
Note: The MFJ Air Core™ Roller Inductor is designed with an exclusive Self-Resonance Killer™ that
keeps potentially damaging self-resonances away from your operating frequency. This feature is
switched in and out of the circuit with a built-in switch in the roller. Therefore, as you turn the
roller up and down, you may feel a bump. This is normal and you should not be alarmed.
Increase the number the controls are set at (on a given frequency) to INCREASE the matching range.
Remember, this LOWERS the efficiency and power handling capability of the tuner.
1. Tune the exciter into a dummy load (most solid state transmitters are "pre-tuned" to 50 ohms and do
not require adjusting with the dummy load).
2. Position the ANTENNA and TRANSMITTER controls at the following settings:
The ANTENNA and TRANSMITTER capacitors have maximum capacitance at setting 0 and minimum
capacitance at setting 10.
Maximum tuner efficiency is achieved with the most capacitance (settings closest to 0) and the least possible
inductance (higher letters of the alphabet). This efficiency translates into best power handling, broadest
bandwidth, and least power loss. The goal is always to operate the tuner at the lowest Q for the LC
(inductance/capacitance) circuit.
When necessary to increase the tuner’s matching range, set the ANTENNA or TRANSMITTER control to a
higher number, or dial in a higher number on the INDUCTOR counter, but remember that this lowers the
efficiency and power handling capability of the tuner.