MFJ MFJ-817C Instruction Manual Download Page 2

MFJ-817C Deluxe VHF/UHF True Peak Reading SWR/Wattmeter 

Instruction Manual

 

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.   

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