MFJ MFJ-853 User Manual
INTRODUCTION
Congratulations on purchasing the MFJ-853 RF-Current Meter. The MFJ-853
is designed for measuring RF current distribution on antenna elements and
radials, ground wires, and coax shields. Here are some important features we
think you'll like:
Range: Measures RF current from as little as 300 mA to 3 Amps in three
ranges.
Low Interaction: Sense coil has minimal effect on circuits under test.
Large Cable Capacity: Accepts cables up to approximately 1/2" in diameter.
Power: No power source needed.
Non-metallic case: Minimizes field disturbance for accurate reading.
Handheld Size: Light weight, only 2.25" x 1" x 3.75"
CONTROLS
1. Sense Coil: Clamps onto conductor under test, accepts diameters to around
1/2" .
2. Meter: Calibrated scale indicates readings in mA or Amps.
3. Range: Selects from three measurement ranges.
OPERATING INSTRUCTIONS
Using the Sense Coil: The sense coil snaps over wires and cables, as shown
below. To unlatch, squeeze the nylon carrier between thumb and forefinger-applying opposing pressure. The coil's top section should move forward
slightly. With pressure applied, lift up to open. Position the wire or cable inside
the core opening. Close th e lid over the cable, pressing dow n until latch clicks
shut.
Unlatch
1 2
Lift
3
Press
Click!
1
Meter: The meter is scaled from 0 to 100. On the 100-mA range, readout is
direct (100 = 100 mA). On the 1-A range, move the decimal point 2 places to
the left (100 = 1.00 A). To convert meter readings made on the 30 mA, 300
mA, and 3-A ranges, multiply accordingly. For example, a reading of 85 on the
300-mA range equals 300 x .85, or 255 mA. The chart below will help you
estimate readings quickly:
Range
Meter 300 mA 1 A 3 A
10 30 0.1 0.3
20 60 0.2 0.6
30 90 0.3 0.9
40 120 0.4 1.2
50 150 0.5 1.5
60 180 0.6 1.8
70 210 0.7 2.1
80 240 0.8 2.4
90 270 0.9 2.7
100 300 1.0 3.0
The <30 mA range is uncalibrated and meter readings represent a relative
indication only. It is normal, at high sensitivity, to see some residual meter
reading (up to 15%).
Range: The Range switch selects between three calibrated scales (from 300
mA to 3 Amps). To prevent meter pegging, begin checks on a high range and
work down. To estimate unknown current levels, use the formula below (I =
Unknown Current in Amps, P = Applied Power in Watts, and R = Load
Resistance in Ohms).
P
I
=
R
RF Hazard--Important Warnings:
1. RF-current measurements must be conducted with extreme caution. Physical
contact with conductors carrying even moderate RF-energy levels can result
in severe RF burns, or injury.
2. Avoid measuring RF current on conductors where high RF voltages may be
present (>500 Volts). Damage to your meter may result.
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