MFJ-994B IntelliTuner Automatic Antenna Tuner
Instruction Manual
©
2004-2010 MFJ Enterprises, Inc.
23
Wattmeter Calibration
To calibrate the wattmeter, you will need a Phillips screwdriver and a tuning tool or small flat blade
screwdriver.
WARNING: Never operate the MFJ-994B with its cover removed; dangerous voltages and
currents can be present during operation. Never exceed tuner specifications.
Note: The trimmers involved in this calibration are located on the circuit board behind the front
panel; do not confuse these with the SWR bridge trimmers.
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. Press and hold
both
the [C-UP] and [C-DN] buttons while turning the power on. Both meter needles
will bounce. Release the buttons.
4. The forward needle will go up. Use a small flat blade screwdriver and adjust the FWD trimpot R75,
located behind the display, to set the forward power needle to the 100-watt mark.
5. Press [TUNE] to calibrate the reflected power needle. The forward needle will drop to zero and the
reflected needle will go up.
6. Adjust the REF trimpot R76, located behind the display, to set the reflected power needle to the 20-
watt mark.
7. Press [TUNE] to resume normal operation.
8. Turn off the tuner power and secure the cover back onto the tuner.
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-994B 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-DN] and [L-DN] 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.