MFJ-989D VersaTuner V
Instruction Manual
15
4.) Disconnect all antennas from your building during lightning storms.
5.) Always tune antennas with low power (25 Watts or less for initial adjustments).
6.) Confirm tuner is adjusted for minimum SWR before applying high power.
7.) Never exceed the 1500-Watt legal power limit through your tuner!
In Case Of Difficulty
1.) Tuner Fails To Reduce SWR:
Double-check all connections and repeat the tuning procedure again.
2.) Tuner Arcs:
If arcing occurs at rated power levels, double-check all connections and repeat the
tuning procedure. Confirm you are using the
least inductance
(highest number) and the
most
capacitance
(lowest number) possible to match the load. If tuner still arcs (especially on 160 Meters),
reduce power and check your antenna system for extreme load conditions.
3.) RFI Problems:
Keep radiating wires such as those feeding classic Windoms, long-wires, Ts, or
inverted-Ls away from other wiring. To further reduce RFI, run the wire parallel and reasonably close to
the station's ground line. Also, use heavily insulated wire wherever possible to prevent arcing!
4.) RF-Grounding:
A good RF ground is essential, especially when using a single-wire feed, because
the tuner needs a counterpoise to help it force current into the radiating line. Lacking a good ground, RF
has a habit of finding its way into power lines (RFI), audio circuits (RF feedback),
and you
(RF burns).
Don't rely on water pipes, short copper rods, or "dc" grounds for a antenna counterpoise. RF grounds
work better when spread out over a large area with multiple connections to the equipment ground point.
A RF-radial system or multi-wire counterpoise is ideal because it provides a large low resistance mat to
reinforce the antenna. If installing a good RF ground isn't possible, it's best to avoid using unbalanced
monopole designs that depend on ground reinforcement. Regardless of antenna type, always use
whatever resource is available (ground rods, pipes, etc) as a
safety ground
for both you and your
equipment.
5.) Skin Effect:
RF and lightning travel on the
surface
of conductors. Braided or woven conductors have
relatively high surface resistance to lightning and RF, so ground leads should always have a smooth
metallic high-conductivity outer layer with as much surface area as possible.
Important Warning: For operator safety, always install a good earth ground and connect it directly to
the case of the MFJ-989D. A terminal post marked GND is provided on the back panel for a secure
connection.
Antenna System Hints
1.) Location:
End-fed long-wires should measure at least one quarter-wavelength at their operating
frequency. Horizontal dipoles should span at least a half-wavelength and be installed as high and in the
clear as possible. Good RF ground systems become especially important when using longwires or other
Marconi-style antennas.
2.) The High-Impedance Problem:
Most matching problems involve high-Z loads appearing at the tuner
end of the feedline. If you feed a low-impedance antenna with an
odd quarter-wavelength
of line, the
load will invert to a high impedance at the far end. And, if you feed a high-impedance antenna with an
