MFJ-842 Mobile VHF/UHF SWR/Wattmeter
Instruction Manual
3
Operation
1. The meter’s full-scale forward and reflected power range is controlled by the
POWER RANGE
button. When the button is pushed
in
, the forward power
scale is on
150 Watts
and the reflected power scale is on
50 Watts
. When the
button is pushed
out
, the forward power scale is on
15 Watts
and the reflected
power scale is on
5 Watts
. If your transmitter/amplifier runs more than 15 Watts
of output power, push the button
in
for 150 Watts.
If your transmitter runs less
than 15 Watts of output power, push the button
out
for 15 Watts.
2. Forward power is displayed on the left-hand FORWARD meter scale. This scale
is calibrated from 0 to 150 Watts and is read directly in the
150W (in)
position.
Each picket (scale mark) represents 5 Watts below 30 Watts, 10 Watts between 30
and 150 Watts. In the
15W (out)
position, the forward power scale must be
divided by 10. Each picket represents 0.5 Watt below 3 Watts, 1 Watts from 3 to
15 Watts.
3. Reflected power is displayed on the right-hand REFLECTED meter scale.
Reflected power is 50 Watts full scale when the
150W (in)
power scale is
selected, and 5 Watts full scale when the
15W
(out)
power scale is selected.
4. The most accurate power readings occur in the upper half of the meter scales.
When trying to measure power with a less than perfect match, the reflected power
should be subtracted from the forward power reading in order to find the true
power. NOTE: In the case of 220 MHz band measurement, both forward and
reflected power must be converted with the following formula:
DIRECT READOUT X 0.7 = ACTUAL POWER
5. The SWR is read directly from nine red SWR curves that range from 1:1 to
∞
.
SWR is measured by observing the point where the forward and reflected power
needles cross. The SWR is indicated by the red curve closest to the needle
crossing point.