MFJ-991 / MFJ-994 IntelliTuner Automatic Antenna Tuners
Instruction Manual
©
2004 MFJ Enterprises, Inc.
20
Frequency Counter Calibration
To calibrate the frequency counter, you will need a transmitter, a 50-ohm dummy load, two 50-ohm SO-
239 coax cables, a Phillips screwdriver, and a tuning tool or small flat blade screwdriver.
WARNING: Do not touch anything inside the tuner during operation! Serious, painful RF
burns can result.
WARNING: Never operate the MFJ-991/4 with its cover removed; dangerous voltages and
currents can be present during operation. Never exceed tuner specifications.
1. Turn off the power to the tuner and the transmitter.
2. Remove the cover from the tuner (12 screws) with a Phillips screwdriver.
3. Connect the 50-ohm dummy load to the ANTENNA connector; connect the transmitter to the
TRANSMITTER connector on the tuner.
4. Turn on the power to the transmitter. Set and lock the transmitter frequency to
exactly
29.000 MHz.
5. Press and hold
both
the [C-UP] and [L-UP] buttons while turning the tuner power on. Both meter
needles will go to full scale.
6. Key the transmitter to output about 10 watts. Adjust trimmer capacitor C118 (located between the
two big integrated circuits) until the tuner’s meter needles settle at the 0 watt marks. Notice the meter
movement is exaggerated for easier calibration. Nominal tolerance of the frequency counter is ±1
kHz.
7. Turn off the power to the tuner and the transmitter.
8. Secure the cover back onto the tuner.
In Case of Difficulty
If the tuner acts erratic, reset the tuner to factory defaults by pressing both the [TUNE] and [L-DN]
buttons while turning the power on. If the tuner fails to tune, please
double check
all connections and
follow the tuning procedures again. Be sure you are using
enough inductance
(through manual
adjustment) and
minimum capacitance
.
If the tuner arcs
at the rated power levels, please
double check
all connections and follow the tuning
procedures again. Ensure you are not exceeding the tuner’s rated power handling capability. If you have
adjusted the tuner manually, be sure you are using the
least amount of inductance
and the
greatest
capacitance
possible that still allows matching the load on the operating frequency.
Note: If the tuner arcs when operating on the 160-meter band, it may be necessary to reduce
transmitter output power.
If you are still unsuccessful, but the tuner does adjust and operate when used with a dummy load or
another antenna, please read “Grounding Hints” and “Antenna System Hints” on page 13.
Summary of Contents for IntelliTuner -991
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