DRAFT Recommended Practice for Measurements and ...

1/29/98 73 C95.3-1991 Revision — 2 nd Draft
10/98 Draft
operation of RF generators with antennas pointed in the direction of personnel.
Before a survey begins, antennas should be adjusted far from the most potentially
hazardous position with the surveyors approaching from out of the beam path
toward the beam. Furthermore, if measurements are to be conducted while the
antenna is scanning, one should first determine whether or not the response time
of the instrument is fast enough to respond to the scanning beam. In addition,
one must be aware of the burnout characteristics of thermocouple type probe
elements which can reach their burnout limit in a pulsed field without reaching the
RMS limit of the probe.
(3) A theoretical examination of the radiation patterns should be made before
beginning actual system operation or conducting the survey.
(4) Antennas should not be pointed toward metal structures, and metal objects
should not be inadvertently located close to antennas. These not only create
scattering and multipath situations, but are also a potential source of RF burns.
However, if the normal area of transmission includes such metal objects,
measurements should be conducted in those areas with the objects in place.
The presence of secondary structures such as towers, guy wires, fences,
reflecting surfaces, etc., can enhance the fields and produce RF hot spots.
Allowance for such effects should be made when undertaking a survey. During
the survey, the surveyor should be in continual communication with the operator
of the RF source so that the source may be controlled in accordance with survey
requirements.
When performing leakage surveys, the following precautions should be taken:
(1) The possibility of leakage exists at the site of the RF generator, along any
transmission line or waveguide conveying power from the generator (particularly
at waveguide joints), and at all access doors and panels of enclosures housing
the generator. Normally, leakage energy drops off as the inverse square of the
distance. Therefore, in conducting a survey, one should begin by approaching the
generator, antenna, or any unintended radiating/leaking structures from a ‘’safe’’
distance. The survey instrument should be set to a ‘’high’’ range to alert the
surveyor of the possibility of over-exposure (for example, greater than 10
mW/cm 2 ).
(2) The possibility of RF burns exists, so contact should be avoided with any metallic
structure on or near a point where high field strengths could exist.
(3) When opening access doors or panels to insert or remove a test load (for
example, in a microwave oven or RF-exposure test chamber), the equipment
should be shut down first and the interlock systems left operative.
(4) In checking for possible inoperative interlocks at an RF enclosure access port,
one should ascertain leakage levels while the source is on and the port is closed.
Then the surveyor may slowly open the port to observe any increase in leakage
and possible interlock failure.
Copyright © 1998 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft,
subject to change.