What is the worst source of RF exposure for most people? In May 2011 a division of the World Health Organization (WHO) classified cell phones as a "possible carcinogen." Using a cell phone next to your ear exposes parts of your brain to an RF electromagnetic field strength of around 10 to 25 W/m2. You can reduce this exposure a lot by using headphones or earbud.
What is an RF Electromagnetic Field? Electric and magnetic fields oscillating in waves at a rapid frequency. It has a frequency in waves per second (in Hz, kHz, MHz, or GHz), and a field strength usually measured in Volts per meter (V/m) and average power usually measured in Watts per square meter (W/m2 or W/sq.m.) or similar unit.
What is frequency in Hz, KHz, MHz, or GHz? Frequency in Hz is how many waves per second. kHz is a thousand waves per second, MHz is a million waves per second, and GHz is a billion waves per second. So 1000 Hz = 1 KHz, 1000 KHz = 1 MHz, 1000 MHz = 1 GHz.
Higher frequency is not necessarily worse than lower frequency. Higher frequency is not the same as higher RF field strength or power.
RF means "Radio Frequency" which are frequencies of a few KHz up to and including MHz and GHz frequencies, such as electromagnetic fields as from cell phones and cell towers, radio towers, and TV towers. RF also includes microwave frequencies.
An RF meter does not measure static or low-frequency fields from magnets, the earth's magnetic field, power lines, or home wiring.
What is W/m2 or W/m.sq. ? "Watts per meter square", used to measure the power and the average power of the electromagnetic field and RF exposure. Sometimes it is converted to "milliWatts per meter square" (mW/m2, where 1000 mW/m2 = 1 W/m2). Other units of RF field strength are: uM/m2, nW/m2, mW/cm.sq. etc, using typical scientific notation.
What is dBm? It is the power received by the RF meter, and can by converted to mW/m2 using a table printed on the front of the meter. The more negative the dBm the less power was received: -30 dBm means 10 times less power than -20 dBm.
Can the RF meter measure RF power from cellular phone towers, TV and radio broadcast towers? Yes, except not AM radio towers since AM frequencies are below the frequency range of this meter.
What are government safety standards for RF exposure? Different countries have different standards and it also depends on the frequency and length of time of the exposure. In the USA the limit for RF average power exposure of the public is:
2 W/m2 at frequencies of 100 MHz to 400 MHz
2 to 10 W/m2 over frequencies of 400 MHz to 2000 MHz
10 W/m2 at frequencies of 2000 MHz to 5000 MHz.
Some countries have lower limits: in Canada it is 3 W/m2 at 1800 MHz (Safety Code 6, 1997).
In Italy, Switzerland, Poland, and China it is 0.1 W/m2 at 1800 MHz.
Note, our RF meter is much more accurate than most RF meters for reading average power levels, as explained at bottom of this page.
You can view the full US government standard at http://standards.ieee.org/about/get/index.html#getC95 , Table 9 of IEEE C95.1-2005 gives the RF exposure limit for the general public. Different regulations apply to cell phone use next to your head, but all the US standards are based on average RF power level to heat human tissue.
There is a cell phone tower near my house, what is our RF exposure, and should we be concerned? RF exposure at ground level from a cell tower is roughly 0.01 W/m2 at 100 yards and 0.005 W/m2 at ½ kilometer (1/3 mile) but this can vary a lot. Whether you should be concerned also depends on how much RF exposure you are willing to live with. According to the "Study of the health of people living in the vicinity of mobile phone base stations" by Santini, people should not live closer than 300 meters (about 1/5 of a mile) from cell phone base stations. Other studies also report ill-health effects by people living close to phone towers: www.powerwatch.org.uk/rf/overview.asp
RF exposure will depend on the distance from the tower, your height above ground compared to the tower antenna height (being closer to the antenna height is worse), the number of carriers and operators using that tower, the average power transmitted, frequencies, antenna patterns, type of walls and roof material in your building, metal objects in your vicinity, etc. You can get some general info about most towers in the USA, such as the tower location and frequency, from www.antennasearch.com . You can also measure the approximate RF exposure using the RF meter and compare it with other locations.
There is an antenna on the roof of my apartment building or nearby building, what is my RF exposure? First, find out what type of antenna and what its used for: some antennas are for receiving only (like TV antennas on houses, satellite TV, and some satellite internet antennas), those would not transmit anything so they would not cause any RF exposure nor show anything on the RF meter. See if the building address is found at www.antennasearch.com which gives some information about many transmitting antennas in the USA. Ask the owner of the building or the antenna what type of antenna it is. If it is a cell phone antenna then see the above FAQ about antenna towers near your house. Antenna beams usually direct more power horizontally than downwards, so you could have more exposure on an upper floor of a nearby building, than on a lower floor in the same building as the rooftop antenna.
Could there be a cell phone antenna on the wall of my building? Sometimes a cell phone company has been allowed by the landlord to place an antenna on the outside wall of an apartment or office building, which exposes the occupants in the nearest room to unusually high RF fields. These antennas may be as small as a shoe-box and painted the color of the exterior of the building to blend in. These antennas can be located using the RF meter, since the fields get stronger as you approach the antenna.
There is a TV tower near my house, what is our RF exposure? Exposure from a TV tower was measured to be around 0.01 W/m2 at a distance of 1/2 mile (800 meters). You can also measure it using the RF meter.
If I want to reduce RF exposure from a nearby tower or antenna, what can I do? Aluminum siding will block most RF radiation. RF waves travel mainly in straight lines from the source and are blocked by metal, so you actually only need the aluminum siding on the sides of the house facing the tower. In attic areas you can staple chicken-wire to block rays from the top of the tower from entering the house from above. Aluminum mosquito screens will block RF and can be used over windows.Conductive fabrics can be used over walls or ceilings or for window drapes (conductive fabrics are usually copper color or gray color and are very flexible and can be sewn like most fabrics). Aluminum venetian blinds (vertical) in front of windows will block most RF. Aluminum foil also blocks RF. These all work due to the high frequency of RF; the RF can still go around it but it is much reduced in strength. (But these methods would not block 60 Hz magnetic fields from power lines, measured with a gaussmeter).
Can the RF meter measure WiFi and Bluetooth? Yes. Distance reduces RF exposure, so you could place the WiFi router away from children's bedrooms, and turn off WiFi devices like laptops at night if they are close to the bed. Different WiFi devices emit differing amounts of RF power. WiFi routers that need to cover a wider area like schools often radiate at higher power, and could be placed farther away from where children sit. Bluetooth radiates lower power than WiFi.
Can the RF meter measure TV or radio sets in my home? No, since TV and radio sets are receive-only and do not transmit any RF power, so there should not be any RF coming out of a home TV or radio antenna. Two-way radios however can transmit and could be measured by this meter.
Can the RF meter measure Specific Absorption Rate (SAR) of a mobile phone? No. SAR is a more complex measurement which involves measuring how much RF power is absorbed by a user’s head. But the RF meter can measure the RF field strength at different distances from the phone, for example if using an earbud, and with the phone off.
Can the RF meter measure Ham Radio antenna transmissions? Not most ham radio transmissions, since they are usually below the 100 MHz frequency which is the lowest frequency measured by this meter.
Is there an easy way to reduce RF exposure? You can use an earbud for most mobile phone conversations. You can check your house using this RF meter, and if only the green lights are lighting up on it, and you don't live near any TV or radio transmitter towers, then you probably have very low RF exposure.
This RF meter provides a much more accurate average RF power reading than most RF meters, why? Most RF meters use a simple formula to compute RF power from instantaneous voltage which vastly overestimates the average power from most modern digital RF signals, which are transmitted in digital bursts. Our RF meter displays a far more accurate true time-averaged power reading of the last 1024 samples, which is a much more accurate method than other RF meters in this price range. This meter is also easier to use, very wide bandwidth (covers a wide range of frequencies), and very sensitive (can pick up weak signals).
© 2013 Magnetic Sciences
