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 head exposes parts of your brain to an RF electromagnetic field strength of around 10 to 25 W/m2. You can reduce exposure a lot by using a headset or earbud. For more info about cell phone radiation see http://news.cnet.com/8301-30686_3-20068419-266/cell-phone-radiation-a-self-defense-guide-faq/
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 also a field strength or power measured in Watts per square meter (W/m2) 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.
What does "RF" mean? It is short for "Radio Frequency" which is a frequency of a few KHz or more, so it includes MHz and GHz frequencies, such as electromagnetic fields as from cell phones and cell towers, radio towers, and TV towers. RF includes microwave frequencies.
What is W/m2 or W/m.sq. ? It is "Watts per meter square" which is the field strength or power of the electromagnetic field and the RF exposure. Another unit is mW/m2 which is "milliWatts per meter square" (1 W/m2 = 1000 mW/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 exposure of the public (averaged over 30 minutes) is 2 W/m2 at frequencies of 100 MHz to 400 MHz, rising from 2 to 10 W/m2 over frequencies of 400 MHz to 2000 MHz, and is 10 W/m2 at frequencies of 2000 MHz to 5000 MHz. 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 phones. These standards are based on the RF exposure required to heat up human tissue.
Some countries lhave lower limits: in Canada it is 3 W/m2 at a frequency of 1800 MHz (Safety Code 6, 1997). In Italy, Switzerland, Poland, and China it is 0.1 W/m2 at a frequency of 1800 MHz. Some studies found adverse health effects below the government guidelines:
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 from a tower will depend on your height above ground compared to the antenna height (being closer to the antenna height is worse), the distance to the antennas, 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 info about most towers in the USA, such as the 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 frequency it is transmitting. Some antennas are used for receiving only, those would not transmit anything (for example antennas for TV reception, satellite TV, and some satellite internet antennas), so those would not cause any RF exposure nor show anything on the RF meter. You can see if the building address is found at www.antennasearch.com which gives frequencies of many transmitting antennas in the USA. Also find out from the owner of the building what type of antenna it is. If it is a transmitting antenna then see the FAQ above 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 in the same building as the 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 (see the Frequency Correction Table on RF meter web page). 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.
How do I use the RF meter? The screen and a row of colored lights both show the RF power received by the meter in units of mW/m2 (1000 mW/m2 = 1 W/m2), and in dBm. However, the meter does not know the frequency of the RF power it is measuring, so for accuracy you need to find out the frequency, and then add the dBm shown on the Frequency Correction Table shown on the web page http://www.magneticsciences.com/RF-Meter.html. The frequencies of many towers in the USA can be found at www.antennasearch.com. More detailed instructions are included with the meter. This meter is much more sensitive than other meters in it's price range, so it can pick up RF signals as low as 0.002 mW/m2
Is there something easy to do if I don't know the frequencies? You can use an earbud for most mobile phone conversations. You can check your house with the 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.
How accurate is this RF meter? The manufacturer says it is accurate to within +/-3.5 dB at the calibration frequency of 1.9 GHz. At other frequencies the dBm adjustment (from the Frequency Correction Table on the web page) is very approximate. This meter is very sensitive (it can pick up weak signals), wideband (picks up lots of frequencies), and low-cost, but not very accurate in order to provide an affordable 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.
© 2011 Magnetic Sciences
