MFJ Enterprises Inc.
Tuners, Wattmeters calibration procedure
mfj-xxx has been calibrated at the factory. IF it should ever need to be recalibrated, then follow this procedure:
Transmitter capable of supplying enough power to obtain 1/2 to full scale reading at 14 or 21 MHz.
50 Ohm dummy load that is capable of handling full power that the transmitter can put out and has better than a 1.15:1 swr.
A power meter of known accuracy. The calibration will only be as good as the reference meter.
50 Ohm cables capable of handling the power. RG-58/U is recommended.
DO NOT USE RG-59 or RG-11.
-- refer to PC layout for trimpot location.
PC BOARD should identify the trimpots as:
HIGH FORWARD, LOW FORWARD, HIGH REFLECT, LOW REFLECT.
Remove the top cover of the MFJ-XXX.
Connect the equipment as shown in the diagram below. Use 50 Ohm dummy load for the antenna. Set the transmitter to 14 MHz band.
Transmit about 100 Watts as indicated on the reference meter. Adjust
to set 100 Watts on the forward power scale. Next set the pushbuttons to
the 2000 Watt power scale. Transmit 1000 Watts as indicated on the reference meter. Adjust
to set 1000 Watts on the forward scale.
To set the reflected power, interchange the transmitter and coax cable so that the
transmitter is connected to the antenna connector and the dummy load is connected to
the transmitter connector. Set the range switch to the 200 Watt range. Transmit 10
Watts as indicated on the reference meter and adjust
to indicate 10
Watts on the reflected scale of the MFJ-XXX. Next set the range switch to the 2000 Watt
scale. Transmit 100 Watts according to the reference meter and adjust
to indicate 100 Watts on the reflected scale.
SWR requires no calibration.
(TRANSMITTER)---(REFERENCE METER)---(TEST METER/TUNER)---(DUMMY LOAD)