MFJ MFJ-818 User Manual

MFJ-818 Mobile SWR/Wattmeter Instruction Manual

MFJ-818 Mobile SWR/Wattmeter

Introduction

The MFJ-818 Mobile SWR/Wattmeter measures forward and reflected power and SWR
simultaneously and is designed to operate on 1.8-30 MHz. The MFJ-818 has two power
scales, which are selected with the top panel push button switch. The high power scale
measures 0-300 Watts forward power and 0-60 Watts reflected power. The low power
scale measures 0-30 Watts forward power and 0-6 Watts reflected power. The MFJ-818
utilizes a large illuminated three-inch Cross-Needle meter to read the SWR from 1:1 to
∞. A slide switch turns the back light on or off. This compact SWR/Wattmeter is rugged
enough to take the abuse of brutal mobile and portable operation.

Figure 1: MFJ Mobile SWR/Wattmeter

Installation

1. Connect your transmitter to the connector labeled TRANSMITTER and your
antenna to the connector labeled ANTENNA. It is important that you use good
quality coax and properly installed connectors.

2. An internal lamp backlights the meter scale. The lamp circuit requires 12 VDC
supply such as the MFJ-1312B. Use a 2.1 mm coaxial plug with the center
conductor positive and the sleeve ground. A slide switch turns the internal lamp
on or off.

3. To measure the power output capability of a transmitter/amplifier you should
connect a quality 50-ohm dummy load to the ANTENNA connector of the MFJ-

818.

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MFJ-818 Mobile SWR/Wattmeter Instruction Manual

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 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.

2. 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.

3. Reflected power is displayed 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.

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.

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.

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