RF Exposure - from the horse's mouth

[KWIDELITZ at delphi.com]

From:   IN%"WOVERBECK at ccvax.fullerton.edu"  6-AUG-1996 22:35:48.20
To:     IN%"kwidelitz at delphi.com"
CC:     
Subj:   A message to forward to the Contest Reflector

                  THE SKY IS NOT FALLING

I understand that some concerns have been expressed about the 
FCC's Report and Order in the RF safety proceeding, which was
released August 1.  I haven't been on the Contest Reflector, 
but I'm told some of the messages posted there lately have
bordered on panic.

As a supporter of the FCC's new rules (and the owner of a 
contest station with four towers), I want to say something:  
the sky is not falling.

I was present when the FCC and EPA conducted their survey
of RF fields at amateur radio stations in 1990.  Let me say
emphatically that the fields at a typical amateur radio station
are nowhere near the levels proscribed in the new rules.  At my
own station, even when I fully telescoped my LM-470 to 25 feet,
the fields inside the house and around the neighborhood were far
below the newly adopted standard.  With the LM-470 fully extended,
the readings on the FCC's high-priced instrumentation were 
miniscule!  The same results were obtained at the homes of
several other hams who run the legal limit and large antennas.

The only installations that approached the FCC's new limits 
were stations that combined moderate or high power and 
antennas within a few feet of the operator, family members 
or neighbors.  Examples or problem installations:

*100 watts into a 146 MHz whip on the roof of a car, with 
people leaning against the car (or in some cases, sitting in 
"hot spots" in the near field inside the car).

*500 watts into a 5-element 50 MHz yagi on a 20' mast mounted
on a van (which produced fields exceeding the standard at 
ground level about 20 feet in front of the antenna, although 
the fields inside the van were safely below the standard).

*VHF-UHF  antennas mounted in the attic of a condominium, 
driven by 100 to 1000-watt transmitters (fields exceeded the
standard in some places below the antenna, probably including 
some areas in neighboring condos).

*The FCC/EPA team didn't measure the fields at any of the 
biggest VHF-UHF mounbounce stations (no owner of such a 
station volunteered to take part in the survey).  However,
a 144 MHz e.m.e. station running 1500 watts into a 24 dBd
antenna array (i.e., roughly 300,000 watts e.r.p.) could 
well generate an RF field in a nearby house that would
exceed the standard.  That is why most e.m.e. operators are 
careful to avoid pointing their antennas at the horizon if 
there are people nearby in the line of fire.

I'm sure none of us would defend installations that expose
unknowing people to RF fields exceeding the standards 
recommended by leading technical organizations such as IEEE, 
with or without an FCC rule.

The van used in the 500-watt six-meter tests described
above was mine.  It's a VHF-UHF contest vehicle capable of
high power all the way up to 1296 MHz.  I have used it at 
full power many times since the FCC/EPA team measured the 
fields, but only in remote areas where there aren't any people 
wandering around in front of the antennas.  Under the new FCC 
rules, it is still be legal to use a van-mounted station 
like this one as long as the owner takes common sense 
precautions.  For example, it's not the station of choice 
to demonstrate amateur radio at the county fair!

I recently wrote a short summary of what Docket 93-62 
actually says.  I'm attaching that to this message.

I want to thank Ken Widelitz, AB6FO, for posting this
on the Contest Reflector for me.  My e-mail address is
woverbeck at fullerton.edu, and I would welcome responses.
I have a slide show on the RF safety issue, including 
Docket 93-62.  I'll be happy to speak on this issue anywhere
that my schedule permits (I have prior plans for the second
weekend in September and four weekends in late October and
November).

73,

Wayne Overbeck, N6NB


************

                A SUMMARY OF DOCKET 93-62

Here are some highlights of the amateur radio portion of ET
Docket No. 93-62, approved by the FCC on Aug. 1, 1996:

1)  Amateur radio stations will no longer be categorically 
exempt from complying with the FCC's RF safety standards.
However, individual amateurs will not be required to perform
the complex environmental assessments that are required of
many other FCC licensees.

2)  The standards for RF safety that amateurs (and other FCC 
licensees) will be required to meet are a combination of the 
1992 ANSI/IEEE standards and somewhat stricter standards 
developed by the National Council for Radiation Protection 
and Measurement.  The standards establish limits for human 
exposure to RF fields; the permissible field strength (or 
"power density") varies by frequency.  The lowest power 
density is allowed in the 30-300 MHz range.  At those fre-
quencies, the exposure limit is 1.0 milliwatt per square 
centimeter in "controlled environments" (averaged over any
six-minute period) and 0.2 milliwatts per square centimeter 
in "uncontrolled environments" (averaged over any 30-minute
period).  Amateurs' own households will fall under the 
standards for controlled environments, while RF fields in 
other areas such as neighbors' homes must not exceed the 
stricter limits that apply in uncontrolled environments.

3)  Amateurs whose output power exceeds 50 watts will be 
required to evaluate their station configuration (including 
power output, antenna gain, frequency, proximity of the antenna
to inhabited areas, and duration of transmissions) to assure
compliance with the new rules.

4)  The FCC will publish charts and tables to help amateurs
determine that their installations and operating parameters
comply with the rules.  There will be examples showing
safe distances from various kinds of antennas with various 
combinations of frequency, power output and transmission
duration.

5)  Five questions concerning RF safety are to be added to each  
of three amateur radio examination elements (elements 2, 3A and 
and 3B).  Application forms for new licenses and renewals will 
require amateurs to certify that they have read and understand 
the new RF safety requirements.

6)  As a practical matter, the new rules will NOT require most
amateurs to modify their stations.  The FCC conducted a 
survey of RF fields near amateur radio stations in 1990 and
concluded that only a few station configurations may result in
exposures that would exceed the new standards.  Potential 
problem areas may include high power mobile installations, 
antennas located indoors or close to neighbors' units in 
apartments and condominiums, and high power VHF-UHF stations 
using very high gain antennas near populated areas (e.g., 
a moonbounce array pointed toward a nearby house).

                                -Wayne Overbeck, N6NB
                                 8/3/96