MFJ-989D VersaTuner V
Instruction Manual
14
MFJ-989D!
Then, reduce
exciter
power to bring output
well below 1500-Watts
before connecting to
your tuner. After it is connected, you can readjust the exciter while monitoring amplifier's power on the
tuner's wattmeter. When running SSB, be sure to use the
SWR / Wattmeter's
PK
(peak power) setting for
a true readings on voice peaks!
Never tune up a BIG amplifier using low drive as a strategy to limit its output power (except as an early
step in the manufacturer's tune-up procedure to reduce component stress). To maintain linearity and
proper loading, these amplifiers should always be tuned to full power following the manual's complete
tuning procedure. Then, and only then, is it acceptable to reduce drive to drop output power. And, even
this strategy may not be foolproof! Most transceivers use ALC voltage to control drive level, and some
radios suffer from severe ALC overshoot. ALC overshoot occurs when the radio's ALC circuit responds
to sudden amplitude changes too slowly, allowing high-power transients to slip past. If strong enough,
these momentary spikes may cause a flashover in the tuner! The best policy is always to match the
power rating of your tuner to the power rating of your amplifier.
Tuner Operating Notes
1.) Tuning Range:
The MFJ-989D uses component values carefully chosen to provide the widest
possible tuning range. However, there are limits! If an extreme load condition requires more or less
capacitance than the network components can provide, SWR may not be reduced to 1:1. Normally, this
isn't a problem, but if the residual SWR is higher than the radio's SWR detection circuitry can handle
(typically 2:1), you may need to change the length of the antenna radiator or its feedline in order to bring
the load impedance back within the tuner's range. Extreme load conditions may also lead to arcing or
component heating in the tuner, so they should always be corrected!
2.) Tuner Settings:
The "C-high L-low" rule of thumb always applies. Look for the lowest knob settings
for the
Transmitter
and
Antenna
controls -- along with the highest
Inductor
counter setting -- when
minimizing SWR.
3.) Inductance-Counter Reset:
If stressed, the
Inductor
counter could slip out of calibration. To correct
the problem, first turn
Inductor
fully counter-clockwise until the inductor roller hits the stop. Then,
using a stiff piece of buss wire, a small screw driver, or a pencil, push the reset button which is accessed
through a hole located to the right of the counter window. This action resets the counter to 000.
4.) Logging:
It pays to log all three tuner settings along with the frequency and antenna in use for each
operating setup you make. Use the blank logging chart provided at the rear of the manual and make a
copy. Not only does logging reduce future set up time to a minimum, it also notifies you immediately if
something has changed out at the antenna site! Commercial stations keep tuner logs, and with good
reason!
Warnings
Here's a recap of some important warnings to keep in mind when operating your tuner:
1.) Install so RF-energized terminals and wires are not exposed.
2.) Never operate the tuner with the cover removed!
3.) Never change the Antenna Selector setting while transmitting.
