MFJ MFJ-815C User Manual

MFJ-815C Deluxe HF True Peak Reading SWR/Wattmeter Instruction Manual

NOTE:

IMPORTANT:

l before attempting to operate this equipment. This

unit does not provide a dc or low frequency earth ground. A separate wire

should be connected from the station ground bus to an electric ground. Do

MFJ-815C Deluxe HF True Peak Reading SWR/Wattmeter

Introduction

The MFJ-815C is a true peak reading SWR/Wattmeter designed to operate on 1.8-30
MHz. This meter uses our TrueActive peak reading circuit to read true peak/average
forward and reflected power and SWR simultaneously. It has 3000/300 Watts forward
and 600/60 Watts reflected power scales. The MFJ-815C utilizes a large illuminated
three-inch Cross-Needle meter to read the SWR from 1:1 to ∞.

Please read entire manua

not place any non-coaxial feed wires near metallic or RF sensitive devices.

Installation

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

2. The MFJ-815C has a TrueActive peak reading circuit that requires a DC power
supply such as the MFJ-1312B in order to function. A 9 VDC may also be
installed inside the meter with a battery clip that is included. The rear panel
accepts a 2.1 mm coaxial plug with the center conductor positive (+) and the
sleeve negative (-). The negative lead is grounded inside the meter. There is no
need to disconnect the battery when using external power.

3. An internal lamp backlights the meter scale. The lamp circuit requires 12 VDC
and will not illuminate with the 9 VDC battery alone.

4. 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 MFJ­815C.

The wattmeter must have a power source in order to function. A nine-volt
battery may be installed in the compartment on the rear panel, or an external

12 VDC source, such as the optional MFJ-1312D power supply, may be used.

Operation

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MFJ-815C Deluxe HF True Peak Reading SWR/Wattmeter Instruction Manual

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
3000/300 Watt button. When the button is pushed in, the forward power scale is
on 3000 Watts and the reflected power scale is on 600 Watts. When the button is
pushed out, the forward power scale is on 300 Watts and the reflected power
scale is on 60 Watts. If your transmitter/amplifier runs more than 300 Watts of
output power, push the button in for 3000 Watts. If your transmitter runs less than
300 Watts of output power, push the button out for 300 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 (out) 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 3000W (in)
position, the forward power scale must be multiplied by 10. Each picket
represents 50 Watts below 100 Watts, 100 Watts from 100 to 1000 Watts, and 250
Watts from 1000 to 3000 Watts.

5. The reflected power is read on the right-hand REFLECTED meter scale.
Reflected power is 60 Watts full scale when the 300W (out) power scale is
selected, and 600 Watts full scale when the 3000W (in) 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.

Calibration

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