RF Field Strength Meter

Model: RFF083

Technically a "power density" meter, the RF Field Strength Meter detects the electric field of radio and microwaves (RF) from .5 MHz to 3 GHz, and expresses the field strength as power density (.001 to 2000 microwatts/cm2).

This is an extremely sensitive meter which can accurately measure RF background even in rural areas far from any transmitters. The meter reads true power density directly on the display. Unlike other low-cost field strength meters, this meters frequency response does not depend on the characteristics of an external antenna; the internal detection system yields a flat response over a very wide range of frequencies.

Accuracy in the FM, TV and cell tower frequency range (30 MHz V 2.4 GHz) is +/-25%. Sensitivity is low by 50% (-3 dB) at the frequency limits .5 MHz and 3 GHz. (Sensitivity is 25% at 5 GHz. That is, you must multiply the reading by 4 when measuring microwaves at that high a frequency. At 10 GHz, sensitivity is about 10%.)

A High-Pass selector switch allows you to measure either the full bandwidth ("Wide" = 0.5 MHz V 3 GHz) or to apply a high-pass filter ("Narrow" = 6 dB/ octive rolloff with a knee at 100 MHz) that effectively allows only 100 MHz to 3 GHz through. In practice, this high-pass selector function can be used to estimate one additional parameter: the average frequency of the RF (if it is in the range 10 MHz V 500 MHz).

The RF Field Strength Meter is directional and it detects only the component of the electric field which has the same polarization as the long axis of the meter. That is, if only a vertically-polarized RF wave is present, but you turn the meter in the horizontal direction, it will essentially read zero. If you subsequently rotate the meter to vertical, it will then read the full power density of the RF wave. Most RF radiation has only vertical electric field, so the full strength can be read by holding the meter vertically. (At the end of this page is more information on how to read radio waves with other polarizations).

The meter has a 4 ½ digit display which reads in three ranges: .001 to 19.999, .01 to 199.99, and .1 to 1999.9 microwatts/cm2. For comparison, a low power 100 milliwatt dipole transmitter (typical 49 MHz cordless phone) produces about .010 microwatts/cm2 at a distance of 50 feet. This is 10x the minimum sensitivity of the meter. A FAST/SLOW update switch is normally set in the FAST position so you can quickly measure changes in the RF level. However, if the field strength is fluctuating rapidly, this switch can be set to the SLOW position, which averages the reading over several seconds.

The "zero" level will shift slightly with temperature. This shift is no more than +/- .010 microwatts/cm2 over the meters operating temperature range of 30X F to 110X F (-1 to 43X C). Two controls on the right side of the meter correct for this: a button, when pressed, turns off the pre-amplifier, so it is the equivalent of zero field. Then an offset control is rotated until the meter reads zero in the most sensitive "19.999" setting. After one minute or more of warm-up, this should be adjusted. Once adjusted, this need not be readjusted unless the temperature changes by more than 5X F. (Then a shift of about .001microwatt  /cm2 will occur).

The RF Field Strength Meter comes with a standard 9-volt battery. A low-battery indicator shows on the display when approximately 10 minutes of battery life remain. Electric current consumption from the battery is about 15 ma, with low battery indication at about 7.6 volts.

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