Electromagnetic Field Survey

Submitted by Ben on Fri, 03/27/2009 - 16:42

image of a cell phone tower from gmu.eduMany of my friends in Fairfield, Iowa, are in an uproar right now about a new cell-phone tower that, unlike the existing two towers on the outskirts of town, is near homes and a few blocks from an elementary school.  Here's some of the existing press about the controversy:

I first heard about the controversy when I passed through Fairfield a few weeks ago.  My friends who picked me up at the train station made a good case for their opposition to the tower.  Don't get me wrong, I think there are good reasons to oppose cell phone towers in one's neighborhood: they're ugly, and they're not good neighbors.

Of course, the site in question is right next to the railroad tracks, which carry some 18 trains a day, and in my experience are uglier and much, much worse neighbors than any tower.  Anyone who lives within half a mile of the tracks is already demonstrating a high capacity for tolerating ugliness and bad neighborliness.  There are also several electrical substations in town, which are also ugly and bad neighbors, but they've been there for decades so no one pays them any mind.

Where I disagree with the protestors is about the possible health effects.  The only mechanism anyone can suggest for health effects is the radio-frequency radiation (RF) put off by the antenna, a kind of electromagnetic field (EMF).  New-age philosophy aside, EMFs are scientifically measurable with instruments, so my question for my friends was, if you're so concerned about exposure, shouldn't you get a meter and actually measure the EMFs in your home, in the existing school building, and at the foot of a cell tower?  Maybe there are other sources of EMFs already in your environment that are far more concerning, such that the cell tower's contribution to your exposure is not significant. 

I know Fairfield well enough to know that this was a rhetorical question, but after asking it a handful of times, I started to wonder, why don't I get a gauss meter and measure some EMFs, so I can show the data to other people?  I just got curious.

CellSensor image courtesy of drgauss.comTurns out, they're quite affordable.  Here's the one I got: http://drgauss.com/ -- I found it for $35 including shipping.  Note that the sales pitch makes it sound like EMFs are quite harmful.  The instruction manual that comes with the device has some similarly alarming claims, but also has a disclaimer saying that the company does not endorse any of those claims!  In other words, they're good enough for the sales team, but not for the guys who write the documentation!

On a side note, the company's other Web site, http://safelevel.com, discredits the stick-on "radiation shields" that many Fairfielders attach to their cell phones, saying, "Other devices that stick to the phone and claim to reduce fields are can actually interfere with reception and cause the phone to emit higher fields than necessary (the phone adjusts its output according to reception quality)." (emphasis added)  But I digress.

So can I measure RF from cell phones, or not?

Anyhow, right after the disclaimer is an introduction that says, "You have purchased a meter that will allow you to detect and measure two very different types of fields."  (emphasis added)  "The first one is the radiation emitted from mobile phones.  It is commonly known as Radio Frequency (RF) radiation.  The second ... is that generated by electrical current.  These fields are known as Power Frequency Electromagnetic Fields ... and are also known as Extremely Low Frequency (ELF) Electromagnetic Fields (EMFs)."

OK, so RF from mobile phones is "very different" from ELFs, being at a higher frequency.  But the meter doesn't distinguish!  It has two scales on its face, but it doesn't give any indication which one to read!  That's a frustration. If only I hadn't just been told that they were very different, I wouldn't mind so much.

So I read on... turns out that the RF the meter was designed to measure was the kind produced by analog phones, and that digital phones (CDMA, PCS, GSM) produce far less radiation over a much wider spectrum for a fraction of the time of their analog counterparts, such that it is nearly impossible to measure the RF output of a modern digital phone.  In fact, after telling you how to do a "bench test" of your phone, the manual admits, "...the meter's readings are not conclusive.  Proper measurements of RF radiation from mobile phones require the use of professional equipment costing thousands of dollars." (emphasis added)

So much for that.  How about other EMFs?

As I understand it, exposure to an EMF has three facets: quality, quantity, and duration. 

Quality is the frequency of the transmission.  Some cell phones (notably the newer, digital ones) operate in the microwave part of the spectrum, and that in itself alarms some people because of the connotation to cooking food, but only a very small range of frequencies will cook food, and the many other uses of microwaves operate outside that range.  Other appliances, as the meter's manual pointed out, are more likely to radiate at the frequency of the AC power they use, which is much much lower than microwaves.

Quantity is the strength of the field, which is what the meter measures, and which decreases inversely with the square of the distance.  So a cell phone antenna 80 feet off the ground would have to be broadcasting at 6400 times the power as a handset one foot away to be more damaging to one's health.  Or sticking to what we can measure, standing 10 feet away from a poorly-shielded appliance would be 1000 times less harmful (presuming for the moment that it is harmful) than standing a foot away.

Duration is a tougher nut to crack, and the one my friends fell back on in our discussions: even if the fields are weak, they say, and even if they are in a harmless part of the spectrum, surely it can't be good to be exposed to them all day long, in one's home or school.  Which is why I bought the meter in the first place: maybe we and our kids are already being exposed to fields all day long in our homes and schools, and we just don't know it!

The meter is easy to use, with a light and sound that come on when the probe measures more than the recommended 2 milliGauss threshold.  The tricky part is that it measures 3-D fields in one dimension, and the fields are amorphous and wiggly, so you have to measure several times to be sure where the 2 mG threshold lies.

Enough talk already.  What did I find?

Here are a few of the more notable fields I found in our home.

source 2 milliGauss threshold ("safe" distance)
electric stove, on high 5 feet from burner
refrigerator, running 5 feet from sides, 1 inch from front
power strip for entertainment center 4 feet
microwave oven, running 2 feet from sides and top, 1 foot from front
microwave oven, standby 1 foot from sides and top, 1 inch from front
media center PC 1 foot from back of case
miscellaneous power adapters 1-2 feet
fluorescent tube light 3 feet from ballast
compact fluorescent light 1 inch from ballast
Sleep Number Bed pump, running 2 feet from pump
laptop computer (LED backlight), running 2 inches from keyboard
LCD computer monitor (fluorescent backlight) 3 inches from center of screen
LCD TV (fluorescent backlight) 2 inches from back of case
cell phone, standby or making call 1 inch from side facing away from head
Bluetooth headset, standby

1 inch from side facing head

  • Wi-fi devices, such as our router or iPod Touch, did not register on the meter at all.  Either their fields are very weak, or they are a frequency the meter does not measure.
  • The power strip for our entertainment center throws more EMF than all the devices plugged into it.
  • The fridge contributes at least as much to our household EMFs as the stove, yet we have no control over when it comes on.
  • I'm sure I get more radiation from my cell phone than from the Bluetooth headset, because I wear the phone in my pocket, but the headset delivers the radiation straight to my head, while the phone sends it away.  Your mileage may vary.
  • If I were a parent concerned about my child's exposure to EMFs, I would be most concerned about fluorescent tube lights and power strips in schools.

I hope you find this useful!  Comments welcome!


Anonymous (not verified)

Sat, 03/28/2009 - 11:17

what about those towers? Wasn't that what drove you to do the testing in the first place?

It was, but it turns out the meter I bought is not appropriate for testing the towers, first because its probe is designed for measuring fields up close, and second because it is not designed to measure the emissions from digital phones, which are far weaker, spread over a wider spectrum, and shorter in duration than the meter can measure.  I would have needed a more expensive meter, at $449 plus shipping.

Moreover, the research I did along the way just reaffirmed my opinion that the emissions from cell towers are not significant compared to other sources.  For example,

He started by testing his wife’s cell phone then moved on to testing students’ cell phones. He only picked up a signal when the person was talking on the phone. In that case, the signal hit the max the meter could read - 1 milliwatt/cm2. He went with his class and stood below the cell tower, where the meter registered almost zero. However, microwave energy fans outwards in a plane, so Knight took another measurement on the second floor of the H Building, outside of the rooms. There he picked up a reading of 0.01 milliwatts/cm2. Inside the rooms, he didn’t pick up anything, which he thinks might be because of the steel in the building.
“If they’re concerned about a tower like this, it seems to me they should probably be concerned about their cell phones, as well,” said Knight.
http://sonomasun.thmm.com/?p=6676 , an article about a science teacher who did his own testing with a handheld meter like the one linked above


The RF levels near a cell tower will not approach Maximum Permissible Exposures at ground level where people are present. Therefore, from a legal perspective, grounds for such an action do not exist...

Protocols for the measurement of RF energy for the purpose of human exposure assessment recommend the use of an "isotropic broadband probe" whenever possible. This type of sensor responds equally to energy arriving from any direction, and over a broad frequency range, as does the human body. Unfortunately ... other signals present near a cell tower will be as strong as the cell phone signals that one is trying to measure. In fact, an FM radio broadcast station a half mile away, and out of sight, can be the strongest signal present near a cell tower...

The variable and cyclic nature of power density levels at the site must be taken into account when performing an assessment. We employ computer data logging to produce a graphic presentation of field strength variation over time. This technique will capture the very substantial field strength transitions that occur with varying levels of cellular usage on the system, and produce a much more meaningful assessment than spot readings with a simple handheld meter.
http://www.emfservices.com/cell-towers.htm , a company that tests emissions exposure for the public


Thanks for the question!

Some readers commented by email.  Here are selected excerpts, ephasis added.

Gordon Stallings wrote,

There are two types of EM fields emanating from a transmitter:  Near and Far.  The near field dies out rapidly with distance whereas the far field is the one that is used for communication, etc.  I suspect that you are detecting the near field from the power strip, etc.
Here's a link on the subject: http://en.wikipedia.org/wiki/Near_and_far_field
and here is a link giving the wavelengths: http://en.wikipedia.org/wiki/Radio_spectrum
Skin effect: http://en.wikipedia.org/wiki/Skin_effect_(electricity)

There are both magnetic and electric fields in an EM wave.  I presume that your meter is measuring the E field.  The E field induces current onto a conductor (antenna) which results in a (time-varying) voltage that is then measured.  Your strong readings near a powerstrip are consistent with this.  It probably doesn't vary with the amount of power that the strip is delivering.

Your readings near the microwave oven are probably entirely ELF from the power circuit.  I looked into getting (or building) a microwave detector.  Although a split grape does well as an indicator of strong microwave fields: http://www.stewdio.org/plasma/  Devising a meter to detect leakage fields is more difficult.  I bought a cheap device for this purpose that turned out to be a liquid-crystal temperature indicator.  Microwave energy would heat the water in the liquid crystal, resulting in a change of color.  Very crude.

Bill Park wrote,

The name "gaussmeter" suggests that it is measuring magnetic, rather than electric fields, because magnetic field strength is measured in gauss, while electric field strength is measured in volts/meter. I suspect it measures low-frequency magnetic fields and RF E/M fields.

Build your own Gaussmeter http://www.coolmagnetman.com/magmeter.htm

Try measuring the 60Hz fields emitted by an electric blanket or heating pad.  They are notorious because the resistive wires in them are usually not run as two parallel conductors, but as a single conductor that zigzags across the blanket. Thus the cylindrical magnetic field around the conductor is not almost canceled by an adjacent, oppositely-directed field from a nearby conductor carrying the same current in the opposite direction, as in any two-conductor electric cord, where the wires are only millimeters apart. And you spend all night a fraction of an inch from the wires!! Hair dryers and barber shears also give off a lot of EM energy.

You probably see a large field around a power strip because the conductors in the strip are separated by the distance between the plug blades, allowing the fields to spread out more, as in the blanket.

Digital cellphones use a spread-spectrum technique to transmit and receive. That means that the RF energy is spread over a much wider range of frequencies than the audio frequency range of the message content.  This allows them to operate even when environmental conditions make some RF frequencies unusable due to absorption by buildings, ground, trees, etc., or to emissions from other sources.  Thus, to measure the power emitted by a cellphone, it is necessary to use a very broadband power meter.  One approach is to convert the RF energy into heat, which then warms a temperature-sensitive resistor (e.g., a thermistor, germanium conductor, etc.), changing its resistance, which is then easily measured even with a simple DC ohmmeter. See "bolometer."

Cellphone antenna design is consequently a true black art, starting with the fact that they routinely make use of fractal antenna shapes to handle the wide bandwidths used.  They are often designed to emit more of the radiation away from your head, but by no means all.  The other components in the phone and even the specific materials in the case all factor into the radiation pattern.

Modern cellphones come with a specification of exactly how much energy they are likely to dump into your brain when used. I've also seen specs on how much you absorb if you carry it on your belt.  This must be required by law or they would never admit how much their phones put out -- it's several watts. Check the user manual. Phones vary by an order of magnitude in this regard. Even when turned on but not being used, the phone transmits intermittently to keep the cell phone tower network apprised of its location.

Incidentally, if you want to absorb lots of EM radiation, just have a CAT scan.  Especially of your head.

My responses:

Bill is correct, although the meter I bought has scales for both mW/cm2 (for measuring cell phone transmissions) and milliGauss, according to the manual it is is the gauss meter that is responding to ELFs from household appliances.  So if I understand correctly, it is measuring the magnetic, not the electric, field from appliances.  I'm not clear on whether that distinction is significant... since both E and M fields are originating from the same cause, aren't they equivalent in strength?

Thanks for the tip about electric blankets!  Unfortunately I can't find ours right now.  I did measure our space heater and found its 2mG threshold at only about 8 inches, similar to our handheld vacuum cleaner.

The cell phones I've bought did come with a notice about how to reduce exposure to radiation, but they didn't say how much energy they radiate, at least not anywhere I could find.  Maybe that's a California thing, Bill?

It seems appropriate that Bill advises anyone who wants to absorb lots of EM radiation to have their head examined.  Preferably by someone else -- Nicola Tesla's X-rays of his own brain probably did more harm than good!