MFJ-818 Mobile SWR/Wattmeter
Instruction Manual
3
Calibration
The MFJ-818 has been calibrated at the factory. If it should ever need to be recalibrated,
then follow this procedure:
Equipment Needed
1. Transmitter capable of supplying enough power to obtain ½ to full-scale reading
at 14 or 21 MHz.
2. 50-ohm dummy load that is capable of handling full transmitter output power and
has better than a 1.15:1 SWR.
3. Power meter of know accuracy. The calibration will only be as good as the
standard reference meter.
4. 50-ohm cables capable of handling the power. RG-58/u is recommended. DO
NOT USE RG-59 or RG-11.
Meter Calibration
1. Refer to
Figure 2
for the Test Setup and refer to the Trim Pot Location in
Figure
3
for trim pot location.
2. Connect the Test Setup equipment as shown in
Figure 2
. Use a 50-ohm dummy
load for the antenna. Set the Transmitter to the 14 MHz in the 20-meter band.
3. With the
POWER RANGE
button pushed
in
for the 300 Watt scale, transmit 100
Watts as indicated on the reference meter. Adjust the HI FWD trim pot to set the
forward power scale to 100 Watts.
4. With the
POWER RANGE
button pushed
out
for the 30 Watt scale, Transmit 10
Watts as indicated on the reference meter. Adjust the LO FWD trim pot to set the
forward power scale to 100 Watts.
5. To set the reflected power, interchange the TRANSMITTER and ANTENNA
coax cables so that the transmitter is connected to the ANTENNA connector and
the dummy load is connected to the TRANSMITTER connector.
6. With the
POWER RANGE
button pushed
in
for the 60 Watt reflected scale,
Transmit 20 Watts as indicated on the reference meter. Adjust the HI REF trim
pot to set the reflected power scale to 200 Watts.
