MFJ-817C Deluxe VHF/UHF True Peak Reading SWR/Wattmeter
Instruction Manual
2
Operation
1. With the DC power supply or 9 VDC battery installed, push the
ON/OFF
button
in
to turn the unit ON. If 12 VDC is used, the lamp will also be turned ON.
2. The meter’s full-scale forward and reflected power range is controlled by the
300/30 Watt
button. When the button is pushed
in
, the forward power scale is on
300 Watts and the reflected power scale is on 60 Watts. When the button is
pushed
out
, the forward power scale is on 30 Watts and the reflected power scale
is on 6 Watts. If your transmitter/amplifier runs more than 30 Watts of output
power, push the button
in
for 300 Watts.
If your transmitter runs less than 30
Watts of output power, push the button
out
for 30 Watts.
3. Average power is measured when the
PEAK/AVG
button is pushed
out.
Peak
envelope power (PEP) is measured when the
PEAK/AVG
button is pushed
in
.
Peak and average power values are equal with steady unmodulated carriers, FSK,
or FM. The meter reading on these modes will be the same whether the
PEAK/AVG
button is pushed
in
or
out.
On SSB, the PEP meter reading should
be twice the average power with two-tone test modulation. On SSB, the ratio of
PEP to average power varies with different voice characteristics. With most
voices, the PEP reading is three to five times higher than the average voice power
reading. The most accurate PEP readings are obtained only with sustained carrier,
voice or two-tone test modulation. During normal voice modulation, the
wattmeter will typically indicate only 70% of the true Peak Envelope Power.
4. Forward power is displayed on the left-hand FORWARD meter scale. This scale
is calibrated from 0 to 300 Watts and is read directly in the
300W (in)
position.
Each picket (scale mark) represents 5 Watts below 10 Watts, 10 Watts between 10
and 100 Watts, and 25 Watts between 100 and 300 Watts. In the
30W (out)
position, the forward power scale must be divided by 10. Each picket represents
0.5 Watts below 1 watt, 1 watt from 1 to 10 Watts, and 2.5 Watts from 10 to 30
Watts.
5. The reflected power is read on the right-hand REFLECTED meter scale.
Reflected power is 60 Watts full scale when the
300W (in)
power scale is
selected, and 6 Watts full scale when the
30W
(out)
power scale is selected.
6. 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.
7. 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.