SAFETY: RF AWARENESS GUIDELINES

Although Amateur Radio is basically a safe activity, in recent years there has been considerable discussion and concern about
the possible hazards of electromagnetic radiation (EMR), including both RF energy and power frequency (50-60 Hz)
electromagnetic fields. Extensive research on this topic is underway in many countries. This section was prepared by members
of the ARRL RF Safety Committee and coordinated by Dr Robert E. Gold, WB�KIZ. It summarizes what is now known and
offers safety precautions based on the research to date.

All life on Earth has adapted to survive in an environment of weak, natural low-frequency electromagnetic fields (in addition to
the Earth's static geomagnetic field). Natural low-frequency EM fields come from two main sources: the sun, and thunderstorm
activity. But in the last 100 years, man-made fields at much higher intensities and with a very different spectral distribution have
altered this natural EM background in ways that are not yet fully understood. Much more research is needed to assess the
biological effects of EMR.

Both RF and 60-Hz fields are classified as nonionizing radiation because the frequency is too low for there to be enough
photon energy to ionize atoms. Still, at sufficiently high power densities, EMR poses certain health hazards. It has been known
since the early days of radio that RF energy can cause injuries by heating body tissue. In extreme cases, RF-induced heating
can cause blindness, sterility and other serious health problems. These heat-related health hazards are called thermal effects.
In addition, there is evidence that magnetic fields may produce biologic effects at energy levels too low to cause body heating.
The proposition that these athermal effects may produce harmful health consequences has produced a great deal of research.

In addition to the ongoing research, much else has been done to address this issue. For example, the American National
Standards Institute, among others, has recommended voluntary guidelines to limit human exposure to RF energy. And the
ARRL has established the RF Safety Committee, a committee of concerned medical doctors and scientists, serving voluntarily
to monitor scientific research in the fields and to recommend safe practices for radio amateurs. ARRL FULL REPORT

These guidelines were developed by the ARRL RF Safety Committee, based on the FCC/EPA measurements of Table 9.2 and other data.

Although antennas on towers (well away from people) pose no exposure problem, make certain that the RF radiation is confined to the antennas' radiating elements themselves. Provide a single, good station ground (earth), and eliminate radiation from transmission lines. Use good coaxial cable, not open-wire lines or end-fed antennas that come directly into the transmitter area.

No person should ever be near any transmitting antenna while it is in use. This is especially true for mobile or ground-mounted vertical antennas. Avoid transmitting with more than 25 W in a VHF mobile installation unless it is possible to first measure the RF fields inside the vehicle.
At the 1-kW level, both HF and VHF directional antennas should be at least 35 ft above inhabited areas. Avoid using indoor and attic-mounted antennas if at all possible.

Don't operate high-power amplifiers with the covers removed, especially at VHF/UHF.

In the UHF/SHF region, never look into the open end of an activated length of waveguide or point it toward anyone. Never point a high-gain,
narrow-bandwidth antenna (a paraboloid, for instance) toward people. Use caution in aiming an EME (moonbounce) array toward the horizon;
EME arrays may deliver an effective radiated power of 250,000 W or more.

With hand-held transceivers, keep the antenna away from your head and use the lowest power possible to maintain communications. Use a separate microphone and hold the rig as far away from you as possible.

Don't work on antennas that have RF power applied.

Don't stand or sit close to a power supply or linear amplifier when the ac power is turned on. Stay at least 24 inches away from power transformers, electrical fans and other sources of high-level 60-Hz magnetic fields.

Table 9.2--Typical RF Field Strengths Near Amateur Radio Antennas.

           A sampling of values as measured by the Federal Communications Commission and Environmental Protection Agency, 1990

Antenna Type    Freq   Power    E Field             Location

                        (MHz)     (W)       (V/m)

Dipole in attic     14.15   100        7-100             In home

Discone in attic   146.5   250        10-27             In home

Half sloper         21.5     1000           50             1 m from base

Dipole at 7-13 ft   7.14     120      8-150              1-2 m from earth


Vertical            3.8          800         180              0.5 m from base

5-element Yagi   21.2    1000       10-20             In shack
at 60 ft
                                                      14             12 m from base

3-element Yagi   28.5      425        8-12             12 m from base
at 25 ft

Inverted V at       7.23    1400        5-27             Below antenna
22-46 ft

Vertical on roof   14.11    140         6-9              In house

                                                35-100              At antenna tuner


Whip on auto    146.5       100     22-75              2 m from antenna
roof

                                                 15-30              In vehicle

                                                      90              Rear seat

5-element Yagi    50.1       500     37-50             10 m from antenna
at   20 ft

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