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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MFJ-815C Deluxe HF True Peak Reading SWR/Wattmeter Instruction Manual
The MFJ-815C has been calibrated at the factory. If it should ever need to be
recalibrated, then follow this procedure:
Equipment Needed
1. Transmitter capable of supplying enough power to obtain ½ to full-scale reading
at 14 or 21 MHz.
2. 50-ohm dummy load that is capable of handling full transmitter output power and
has better than a 1.15:1 SWR.
3. Power meter of know accuracy. The calibration will only be as good as the
standard reference meter.
4. 50-ohm cables capable of handling the power. RG-58/u is recommended. DO
NOT USE RG-59 or RG-11.
Meter Calibration
1. Refer to Figure 1 for the Test Setup and refer to the PCB layout in Figure 2 for
trim pot location.
2. Remove the top of the MFJ-815C.
3. Connect the Test Setup equipment as shown in Figure 1. Use a 50-ohm dummy
load for the antenna. Set the Transmitter to the 14 MHz in the 20-meter band.
4. With the 3000/300 Watts button pushed out for the 300 Watt scale, Transmit 100
Watts as indicated on the reference meter. Adjust the LO FWD trim pot to set the
forward power scale to 100 Watts.
5. With the 3000/300 Watts button pushed in for the 3000 Watt scale, Transmit
1000 Watts as indicated on the reference meter. Adjust the HI FWD trim pot to
set the forward power scale to 1000 Watts.
6. To set the reflected power, interchange the TRANSMITTER and ANTENNA
coax cables so that the transmitter is connected to the ANTENNA connector and
the dummy load is connected to the TRANSMITTER connector.
7. With the 3000/300 Watts button pushed out for the 60 Watt reflected scale,
Transmit 10 Watts as indicated on the reference meter. Adjust the LO REF trim
pot to set the reflected power scale to 10 Watts.
Meter Calibration (cont.)
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MFJ-815C Deluxe HF True Peak Reading SWR/Wattmeter Instruction Manual
8. With the 3000/300 Watts button pushed in for the 600 Watt reflected scale,
Transmit 100 Watts as indicated on the reference meter. Adjust the HI REF trim
pot to set the reflected power scale to 100 Watts.
9. SWR requires no calibration.
Transmitter/
Transceiver
Standard
Reference
Wattmeter
MFJ-815C
SWR/
Wattmeter
50-Ohm
Dummy Load
Figure 1: Test Setup
LO REF
LO FWD
HI REF
HI FWD
Figure 2: PCB Layout and Trim Pot Location
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MFJ-815C Deluxe HF True Peak Reading SWR/Wattmeter Instruction Manual
Technical Assistance
If you have any problem with this unit first check the appropriate section of this manual.
If the manual does not reference your problem or reading the manual does not solve your
problem, you may call MFJ Technical Service at 662-323-0549 or the MFJ Factory at
662-323-5869. You will be best helped if you have your unit, manual and all information
on your station handy so you can answer any questions the technicians may ask.
You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial Park Road,
Starkville, MS 39759; by Facsimile (FAX) to 662-323-6551; or by email to
techinfo@mfjenterprises.com. Send a complete description of your problem, an
explanation of exactly how you are using your unit, and a complete description of your
station.
Schematic
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