How is Radio Frequency Measured?
by Amy O’Hair
How do you measure RF?
Let’s start with the units used to measure RF fields in the environment.(Or you can skip ahead to rest of story.)When measuring radio frequency strength in terms of public exposure,
you are looking for “power density”: that is how much radiating energy
is hitting a surface (like your body’s surface). If you’ve read about
RF, you may have seen figures like this: µW/cm². That means “micro-watts
per square centimeter.” (‘Micro’ is represented by a Greek letter ‘mu’ µ
and means ‘one millioneth’.)
That is to say, µW/cm² equals the number of millionths of a watt that
are hitting a surface the size of a pinky fingernail. Some people use a
different measurement: µW/m², microwatts per square meter, which is how
many millionths of a watt are hitting a surface the size of a car rear
window. (Your body surface is about 2 square meters total.)
Either unit can be used to represent a power density measurement. To compare the two units: 1 µW/cm² = 10,000 µW/m².
That’s because you can fit ten thousand fingernails on a car rear
window—10,000 square centimeters inside 1 square meter. Some people who
are interested in small amounts of RF that can affect people use the
second, smaller unit. It’s like if you were to describe how much water
you drink a day, you’d say “32 ounces of water,” not “0.08 barrels of
water” or “0.00125 cubic yards of water.” For sensitive measurements,
use the fine-grained unit. Since biological effects have been observed
down to low numbers of µW/m², that smaller unit is useful for talking
about optimal human health conditions. Here’s a chart that lines up all the dozens of different units that electrical engineers use (yes, there are more). Here’s a calculator.
Power density is not the same as the power of the transmitter, but a
stronger transmitter will create a larger power density. RF power
density drops in intensity off the farther away you are from the
transmitter, which is why, for example, people with smart meters near
their beds are often the ones to complain of insomnia or waking with
Congratulations, if you read and understood this
section, you now know more about RF power density than 99.9% of the
government officials who rubberstamp the wireless industry’s endless
applications for more cell antennas. That’s enough on units for now–on with the story….
Low power is the norm for many wireless transmitters
A microwatt doesn’t seem like much, does it? But many
radio-frequency transmissions, it turns out, don’t require a lot of
power, depending on how far they must go before reaching a receiver.This is part of the reason wireless
communication is often a cheap way to transmit data; local transmitters
can use small amounts of energy. And of course, there is no costly
cable to lay. In many places now you can see wireless antennas on pole
tops with no wired-in electricity, just a small solar panel for power. WiFi transmitters can reach hundreds of feet with just a third of a
watt. Your cell phone can operate with a half- or even a quarter-watt.
The older high-power cell phones used to go dead fast because they
sucked a lot out of their batteries.
The FCC says the transmitter in a smart meter is supposed to be limited to 1 watt
, but we’ve learned in the last year that the antenna pumps that up toan effective power of 2.5 watts.In addition, smart meters contain a capacitor or a battery that produces, at the moment of transmission, a burst of power. Think
of flash units on cameras, which build up power in a capacitor, then
release it all suddenly at the moment of the flash, making an intensely
bright light, but only for a fraction of a second.We’d like to
know how much power all that adds up to in the smart meter at the
moment of the RF pulse, but smart meter manufacturers won’t release the
specifications on their products or components.
That is not to say that wireless networks overall don’t use an
enormous amount of power–they do. Cell antenna arrays can have huge
power draws. But the RF transmitters which you come into close contact
with every day are in general low power.
Low power RF doesn’t mean low biological effect
RF transmitters with small amounts of power have definite effects on bodies.As
biological organisms, we produce millions of tiny electrical signals
internally—regulating our heart, our nerves, our cellular metabolism. In
medicine, there are procedures that use RF with small amounts of power,
to produce distinct changes in the body. This new treatment kills the malaria parasite with cellphone-strength RF (less than 1 watt),while the researchers blithely state that it shouldn’t be used for the head or torso area.This treatment for liver cancer uses low-power RF targeted to kill the tumor cells.
How could the FCC—whether or not they have doctors on staff (they
don’t)—approve the RF used in medical devices, and then not wonder about
what is happening in the bodies of the untold numbers of people being
exposed to fields that are several thousand times stronger? They don’t wonder; it’s not their job.
The FCC limits are a terrible joke
So, what are those sky-high limits on RF that the FCC has set?At the cell-phone and smart-meter range of frequencies, the FCC says
that a field with an average power density of about 600 µW/cm²
(6,000,000 µW/m²) is okay for humans for 30 minutes. Above that, your
tissues begin to heat up, something everyone agrees isn’t good.
That’s average power density.I’m not sure I can emphasize this point enough: inside
that 30 minutes, there could be a great number of peaks at much higher
levels—just as long as the average reading comes out below that
Continued on "Time Averaging RF Erases Peak Spikes"