MFJ-925 Super-Compact IntelliTuner Automatic Antenna Tuner
Instruction Manual
©
2006 MFJ Enterprises, Inc.
19
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-925 with its cover removed; dangerous voltages and
currents can be present during operation. Never exceed tuner specifications.
1. Turn off the power to the transmitter and the tuner.
2. Remove the cover from the tuner (10 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 frequency to
exactly
29.000 MHz.
5. Press and hold
only
the [ALT] button while turning the power on. Both LEDs will blink until the
button is released.
6. Within four seconds of releasing [ALT], press the [TUNE] button six times.
7. After releasing [TUNE] for four seconds, the green LED lights up and the Frequency Counter
Calibration is initiated.
8. Key the transmitter to output about 10 watts and adjust trimmer capacitor VC3 (located next to
the big integrated circuit on the front side of the front panel circuit board) until both LEDs are
lighted up. The green LED lights when the calibration is below 29 MHz, the red LED lights
when the calibration is above 29 MHz and both LEDs light up when the calibration equals to 29
MHz.
9. Unkey the transmitter. Turn off the power to the transmitter and the tuner.
10. Secure the cover back onto the tuner.
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, a tuning tool
or small flat blade screwdriver, and a cross-needle wattmeter (available only at MFJ factory). Therefore,
this calibration can only be done at MFJ factory.
WARNING: Do not touch anything inside the tuner during operation! Serious, painful RF
burns can result.
WARNING: Never operate the MFJ-925 with its cover removed; dangerous voltages and
currents can be present during operation. Never exceed tuner specifications.
1. Turn off the power to the transmitter and the tuner.
2. Remove the cover from the tuner (10 screws) with a Phillips screwdriver.
3. Connect the cross-needle wattmeter to header HD1, located behind the front panel circuit board.
4. Connect the 50-ohm dummy load to the ANTENNA connector; connect the wattmeter between
the transmitter and the TRANSMITTER connector on the tuner.
5. 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.
Summary of Contents for MFJ-925
Page 2: ......
