MFJ-998 Legal Limit IntelliTuner Automatic Antenna Tuner
Instruction Manual
©
2007-2010 MFJ Enterprises, Inc.
30
SWR Bridge Calibration
To calibrate the SWR Bridge, you will need a transmitter capable of 100 watts output, a precise calibrated
wattmeter, a 50-ohm dummy load, three 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-998 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 1 connector; connect the wattmeter between the
transmitter and the TRANSMITTER connector on the tuner.
4. Turn on the power to the transmitter. Using a frequency in the middle of the HF band, such as 7.253
MHz, for calibration is recommended.
5. Press and hold
both
the [C-UP] and [L-UP] buttons while turning the tuner power on.
6. A message
CAL CAP AND FWD
will display. Key the transmitter to output 100 watts and adjust
trimmer capacitor VC1 (located on the small circuit board mounted in front of the TRANSMITTER
connector) for minimum reflected power. Notice the reflected meter movement is exaggerated for
easier calibration.
7. Key the transmitter to 100 watts output and adjust the FWD trimpot VR1 (located next to the big
integrated circuit) until the display shows forward power of
FWD=100
watts. The forward meter also
should indicate 100 watts.
8. Press the [TUNE] button. A message
REVERSE, CAL REF
displays and the reflected meter goes
to full scale.
9. Turn off the transmitter and reverse the ANTENNA 1 and TRANSMITTER connections; that is,
connect the 50-ohm dummy load to the TRANSMITTER connector and connect the
transmitter/wattmeter to the ANTENNA 1 connector.
10. Turn on the transmitter’s power.
11. Key the transmitter to 100 watts output and adjust the REF trimpot VR2 (located next to the big
integrated circuit) until the display shows reflected power of
REF=100
watts. The forward meter
(yes, the forward meter) also should indicate 100 watts; the reflected meter is at full scale.
12. Press the [TUNE] button to end calibration.
13. Turn off the power to the tuner and the transmitter.
14. Remove the transmitter/wattmeter and the 50-ohm dummy load from the tuner.
15. Secure the cover back onto the tuner.
16. Connect your transmitter to the TRANSMITTER connector and connect your antenna to the
appropriate antenna connector on the tuner.