MFJ-986Differential-TTuner Instruction Manual
3
MFJ-986 Differential-T
™
Tuner
Introduction
The MFJ-986 roller inductor tuner is a 3000 watt PEP input, 1500 watt PEP output antenna tuner. These
power ratings are for load impedances of 35-500 ohms. The MFJ-986 is designed to match 50 ohm
output amplifiers, transmitters or transceivers to virtually any antenna. Peak and average forward
power, reflected power, and SWR are displayed on the MFJ-986's illuminated cross-needle meter.
The MFJ-986 Differential-T 3kW Tuner uses a differential capacitor to make tuning easy. It
continuously tunes all frequencies from 1.8 through 30 MHz, including MARS and all the WARC
bands. It will match dipoles, inverted-vee's, verticals, mobile whips, beams, random wires, and many
other antennas. The roller inductor lets you tune down your SWR to the absolute minimum. The MFJ-
986 also features a peak reading cross-needle, SWR/Wattmeter, and a new current balun that will work
with balanced open wire, twinlead, or twin-axial feedlines.
An internal six position antenna-selector switch selects two coaxial line outputs, a single wire line-
balanced line output, or an external dummy load connection. The coaxial line outputs can be selected in
tuned (with tuner's matching network in line) or direct (no matching circuit) configurations.
Understanding Power Ratings
There are no standardized power rating systems for tuners. The names used (i.e. 3 kW Tuner) carry over
from the time when amplifiers were rated by peak power input, and not the true RF power output. For
example, the one thousand watt Johnson Matchbox was rated to handle a 1000 watt plate modulated AM
transmitter (four kilowatts PEP transmitter input and 3000 watts PEP RF output). The Heathkit SB-220
was called a two kilowatt amplifier, and the rated CW output was approximately 600 watts. Matching
tuners were called 2 kilowatt tuners, and these tuners safely handled 600 watts of CW power and 1200
watts PEP SSB.
The FCC has changed the power rating system of amplifiers, and tuners no longer follow amplifier
power ratings. Most typical 1500 watt tuners remain able to safely handle 400-600 watts CW, and 600-
900 watts PEP SSB.
Load conditions and control settings also greatly affect the power handling capability of the tuner. T-
networks typically handle more power on higher frequency bands into higher load impedances. The
worst operating condition for T-network tuners are low impedance capacitive reactance loads. T-
network tuners always handle the least power when operated on 160 meters into low impedance
capacitive reactive loads.
Follow the guidelines in this manual to avoid exceeding the ratings of this tuner.
