ARRL

ARRL General Bulletin ARLB049 (1997)

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ARLB049 RF exposure update

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ARRL Bulletin 49  ARLB049
From ARRL Headquarters
Newington CT  August 26, 1997
To all radio amateurs

SB QST ARL ARLB049
ARLB049 RF exposure update

The FCC has revised the power level thresholds to trigger a routine
Amateur Radio station RF exposure evaluation, and the changes will
be welcome news for most hams. When the FCC first decreed a year ago
that ham radio stations would have to comply with RF exposure
guidelines, it set a 50-W threshold level. The updated guidelines,
announced August 25, increase that threshold level on all HF bands
except 10 meters, where it remains at 50 W. The FCC made no changes
in the RF exposure limits it announced last year.

The new RF safety guidelines are scheduled to become effective
January 1, 1998, for Amateur Radio stations.

The FCC went along in part with a request by the ARRL to establish a
sliding scale for threshold levels, depending upon frequency. The
revised thresholds are 500 W for 160 through 40 meters, 425 W on 30
meters (where the maximum permissible power is 200 W), 225 W on 20
meters, 125 W on 17 meters, 100 W on 15 meters, 75 W on 12 meters
and 50 W on 10 meters. The threshold for all VHF bands is 50 W. On
UHF, the threshold level is 70 W on 70 cm, 150 W on 33 cm, 200 W on
23 cm, and 250 W on 13 cm and above. Stations operating at or below
these respective power levels are categorically excluded from having
to perform a routine RF radiation evaluation. However, all stations,
regardless of power level, still must comply with the RF exposure
limits.

Along with its August 25 Second Memorandum Opinion and Order
announcing the changes, the FCC released the ''core'' text of its
long-awaited Office of Engineering and Technology (OET) Bulletin 65,
Evaluating Compliance with FCC Guidelines for Human Exposure to
Radiofrequency Electromagnetic Fields. The bulletin contains generic
equations that can be used to analyze fields due to almost all
antennas, although the FCC warns that ''the resulting estimates for
power density may be overly conservative in some cases.'' Hams leery
of formulas might opt to wait for the easier-to-use Supplement B to
OET Bulletin 65, which will include information designed
specifically for evaluating Amateur Radio installations. The
supplement promises to detail how hams can determine more simply if
their individual stations comply with the new regulations. The FCC
says the supplement will contain ''information on projected minimum
exclusion distances from typical amateur antenna installations.''

The FCC said it would issue Supplement B ''as soon as a review of
the current draft is complete.''  When it's ready, Supplement B will
be available to download from the FCC's Web site,
http://www.fcc.gov/oet/rfsafety. The FCC directed inquiries as to
the availability of the supplement and other RF-related questions to
its RF Safety Program, 202-418-2464; e-mail rfsafety@fcc.gov.

Last year, the FCC established time-averaged maximum permissible
exposure (MPE) limits for RF fields in two tiers--for controlled
environments (ie, a ham's immediate household, including visitors)
and uncontrolled environments (ie, neighbors, the general public).
If a routine evaluation of a ham station indicates that human
exposure to RF fields could be in excess of the FCC's MPE limits,
the licensee must act to correct the problem and ensure compliance.
This could include changing operating patterns, relocating antennas,
restricting access, changing frequency, output power or emission
type or any combination of these and other remedies.

The FCC says that ham radio facilities ''represent a special case
for determining exposure, since there are many possible antenna
types that could be designed and used for amateur stations.''

The revised regulations categorically exclude most mobile
installations, including those in the Amateur Radio Service, from
having to comply with the RF-exposure or station evaluation
guidelines. Since the FCC issued its guidelines, additional
questions on RF safety have been added to the Amateur Radio
examination question pool.

OET Bulletin 65 and the FCC Second Memorandum Opinion and Order are
available at http://www.fcc.gov/oet/dockets/et93-62/. More details
on the FCC's latest announcement on RF safety will appear in the
October issue of QST.
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