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Measure forward power and reflective power RF levels (MFJ-874 meter)

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Applies to: Transmitter with external antenna

The steps below provide the Instructions to measure the forward (output) power and reflective power levels Transmitter with an external antenna.

Warning

Do not perform this procedure on a 1 Watt Transmitter with an internal antenna or a Repeater Transmitter.

What's required

This testing procedure requires a MFJ-874 Grandmaster SWR & Power Meter. Primex part number WATTMTR-1. Includes meter, two connectors and 24 in. coaxial cable.

mjf-all.png

Step 1: Measure forward (output) power

  1. Power down the Transmitter. Failure to power down will result in damage to the Transmitter.

    1 Watt Transmitter: Power down by unplugging its power supply. From its front panel, verify its LED indicators are not illuminated.

    5 & 30 Watt Transmitter: Power down by setting the power toggle switch, located on the back panel, to the off (down) position.

  2. Set the MJF meter settings.

    VHF/UHF/HF button: OUT position.

    FUNCTION dial: set to FWD position.

    RANGE dial: set to model testing as specified below.

    • 1 Watt Transmitter: 5W

    • 5 Watt Transmitter: 20W

    • 30 Watt Transmitter: 200W

  3. From the MFJ meter, screw the two supplied connectors into the back right side of the meter. Transmitter operates on 72 MHz, between 1.8-200 MHz.

    mjf-connector-1.png
    mjf-connector-2.png

  4. Connect supplied 24 inch coaxial cable to the MFJ meter port labeled TRANSMITTER and the other end into the Transmitter.

    mjf-coax.png

  5. From the Transmitter, disconnect the LMR 400 cable that leads to the external antenna. Then connect the LMR 400 cable to the MFJ meter port labeled ANTENNA. 1 Watt Transmitter connection (not pictured) has the same threading.

    mjf-lmr.png

    Note

    Be sure the cable connections are tightened snug; not over tightened to avoid inaccurate readings or damaged to the Transmitter.

  6. Power on the Transmitter. Once the Transmitter receives its time signal (GPS or NTP), it automatically begins broadcasting.

  7. Once the Transmitter is broadcasting, record the Forward Power measurement.

    Expected measurement by model below.

    • 1 Watt Transmitter: approximately 1 watt; typical value for this model.

    • 5 Watt Transmitter: between 8 to 14 watts; typically 8 watts for this model.

    • 30 Watt Transmitter: between 40 to 60 watts; typically 50 watts for this model.

    The image below illustrates the lines to look at when measuring FORWARD POWER (FWD) based on RANGE.

    mjf-foward-power.png

    Correct Transmitter selections for the RANGE selection (top to bottom).

    • 30 Watt Transmitter: 200W (line 1)

    • 5 Watt Transmitter: 20W (line 2)

    • 1 Watt Transmitter: 5W (line 3)

    Forward Power measurement of a 5 Watt Transmitter.

    mjf-foward-power-5-watt.png

  8. If the Forward Power is below the expected measurement, refer toTroubleshooting Transmitter with External Antenna - Low Forward Power or High Reflective Power Levels

Step 2: Measure reflective power

  1. Set the MJF meter settings.

    FUNCTION dial: set to REV

    RANGE dial: for all models set to 5W

  2. Record the measurement using the lowest line on the MFJ meter.

    mjf-reflective-power.png

    Expected Reflective Power measurement by model specified below.

    • 1 Watt Transmitter: less than 0.1 watts

    • 5 Watt Transmitter: less than 0.3 watts

    • 30 Watt Transmitter: less than 1.75 watts

  3. If the Reflective Power is above the expected measurement, refer to Troubleshooting Transmitter with External Antenna - Low Forward Power or High Reflective Power Levels

Step 3: Return Transmitter back to normal operation

  1. Power down Transmitter.

  2. Disconnect two coaxial cables from the back of the MFJ meter and Transmitter.

  3. Reconnect LMR 400 coaxial cable to the back of the Transmitter.

  4. Power on Transmitter.

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