Alinco DX-801 Instruction Manual download pdf (Page 26)

MFJ-925 Super-Compact IntelliTuner Automatic Antenna Tuner Instruction Manual

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.

6. Press and hold only the [ALT] button while turning the power on. Both LEDs will blink until the

button is released.

7. Within four seconds of releasing [ALT], press the [TUNE] button seven

times.

8. After releasing [TUNE] for four seconds, the cross-needle wattmeter shows 100 watts forward

and 20 watts reflected and the SWR Bridge Calibration is initiated.

9. Make sure the cross-needle wattmeter reads 100 watts forward and 20 watts reflected. If not,

calibrate the cross-needle wattmeter.

10. Press the [TUNE] button and both meter needles drop to 0 watt marks.

11. Key the transmitter to output 100 watts and adjust trimmer capacitor VC1 (located in front of the

TRANSMITTER connector) for minimum reflected power. Notice the reflected meter movement

is exaggerated for easier calibration.

12. Key the transmitter to output 100 watts and adjust the FWD trimpot VR1 (located next to the

RADIO INTERFACE connector) until the forward meter shows 100 watts.

13. Press the [TUNE] button and the reflected meter goes to full scale.

14. Turn off the transmitter and reverse the ANTENNA and TRANSMITTER connections; that is,

connect the 50-ohm dummy load to the TRANSMITTER connector and connect the

transmitter/wattmeter to the ANTENNA connector.

15. Turn on the transmitter’s power.

16. Key the transmitter to output 100 watts and adjust the REF trimpot VR2 (located next to the

RADIO INTERFACE connector) until the forward meter (yes, the forward meter) shows 100

watts; the reflected meter is at full scale.

17. Press the [TUNE] button to end calibration.

18. Turn off the power to the transmitter and the tuner.

19. Remove the cross-needle wattmeter from header HD1.

20. Remove the transmitter/wattmeter and the 50-ohm dummy load from the tuner.

21. Secure the cover back onto the tuner.

22. Connect your transmitter to the TRANSMITTER connector and connect your antenna to the

ANTENNA connector on the tuner.

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Alinco DX-801 Instruction Manual Page 26

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