Thinking of buying an EMF meter? The wide range of EMF meters available on Ebay can make this a difficult decision. A search will typically find digital meters, analogue meters, gauss meters, ghost meters, tri-field maters and tri-axial meters. Confused? This guide aims to provide a basic introduction to EMFs and assistance with selecting an EMF meter.
EMFs or ElectroMagnetic Fields are a way of describing how electric and magnetic forces behave and interact in the space around us. As the name suggests, an EMF has two components; an electric field and a magnetic field. An EMF meter may measure either component or both.
EMFs span a wide spectrum and are commonly described by their frequencies expressed in Hertz (Hz). For higher frequencies the numbers can become a little unwieldy so we also use kHz (1000 Hz) MHz (1 million HZ) and GHz (1000 million Hz). Some typical frequencies found in or around the home are:
0.1Hz to 30Hz 'Brainwaves'!
7.83Hz 'Schumann resonance'
16.7Hz Electric Traction systems (Europe)
50Hz The building mains supply (UK and Europe)
60Hz The building mains supply (USA)
1kHz to 1MHz Switched mode power supplies, inverters
20kHz to 50kHz Compact fluroescent lights (CFLs)
150kHz to 1600kHz AM radio broadcasts
27MHz CB radio
35MHz and 40Mhz. RC models
88MHz to 108MHz FM radio broadcasts
380MHz to 400MHz TETRA digital radio
466MHz PMR446 personal 2-way radio
470MHz to 854MHz Television broadcasts
800, 900, 1800 and 2100MHz Mobile phones
1.9GHz (1900MHz) cordless DECT phones
2.4GHZ to 2.5GHz wifi (wireless-b, -g and -n), bluetooth, RC models, mice, doorbells...
2.45GHz microwave ovens
5.15GHz to 5.85GHz wifi (wireless-a and -n) and fixed wireless data links
For convenience (although these are not the 'proper' definitions) we can refer to the frequencies around about 50Hz as extra low frequency (ELF), those above 1GHz as microwaves and those in between as radio frequency (RF). So, if we need a meter to check the fields from household wiring and appliances we need a meter for 50Hz or ELF. If it is required to measure fields from mobile phones we need a meter to measure RF and microwaves. Typically, a meter for measuring ELFs might have a frequency range from 30HZ to 2kHz and one for measuring RF from 50MHz to 3GHz or, for a more expensive meter, 1MHz to 8GHz. The recent addition of compact fluorescent lamps to the home requires a meter with a VLF range - 2kHz to 100kHz - if their fields are also to be measured.
The next thing to consider is the sensitivity of the meter. Most ELF meters measure the magnetic field in Gauss or Tesla. Since household values are normally low, these would be expressed as mG (thousandths of a Gauss) or uT (millionths of a Tesla). Recommended household ELF EMFs are below 2mG (or 0.2 uT - 1mg is equivalent to 0.1uT) and for most people a meter measuring from 1mG to at least 20mG is adequate for home or office surveys. However. anybody who has been diagnosed as electrosensitive will need a more sensitive EMF meter and/or a meter for ELF voltage fields. For testing the fields directly under overhead power lines a meter measuring up to 500mG is preferred.
RF and microwave meters generally measure the voltage field in volts per metre (V/m, or for smaller fields, mV/m) although they often use this measurement to calculate and display the power density in watts per square metre (W/m2). This a large unit for general use, so instead we might use uW/m2, uW/cm2, mW/m2 or mW/cm2. Very confusing. For home or office use we would ideally like a meter that measures down to 1uW/m2 (or 0.0001uW/cm2 since 1cm2 is one ten thousandth of 1m2).
Analogue display - with a dial and needle.
Analogue signal - smoothly varying, easy to measure an average value.
Broadband meter - measures a range of frequencies, producing a single readout for them all.
Digital display - numeric display, usually a LCD.
Digital signal - pulses at varying intervals, difficult to measure a consistent value under all conditions.
Elecrosmog- refers to the sum of EMFs as a pervading, pollutant smog.
ELF - extra low frequency
Gauss meter - measures magnetic fields in Gauss or Tesla. Sometimes called a Tesla meter!
Ghost meter - Usually a Gauss meter.
RF - radio frequency.
Trifield meter - measures 3 different fields, typically ELF magnetic, ELF voltage and RF voltage.
Triaxial - measures fields in 3d with 3 individual sensors. Costs 3 times as much!
VLF - very low frequency.
Why does my meter give different readings depending on how I hold it? Meters with a single sensor will give a different reading depending on how they are oriented to the field. Take three readings at right angles and do some maths, or for simplicity just take the largest reading as you twist the meter about; the actual field strength will be betweeen one and one and a half times this reading. Or buy an isotropic meter (which usually has a triaxial sensor) which will be independent of orientation. Note that many RF meters have an internal sensor (aerial or antenna) which should not be covered by the hand. Hold the meter by the bottom edge if possible.
Can I measure mobile phone mast signals with an ELF meter? No, you cannot.
Can I measure the field from powerlines with a RF meter? No, you cannot.
Why does my meter give different results to someone else's? Well, when there were just analogue signals, and not many of them, it was relatively easy to measure those signals. Now, in the digital age and particularly at microwave frequencies, there are very many digital signals of many different types and it is much harder to decide on a definitive method of measurement. Meters from different manufactures will probably calculate this differently. Also, the meters may have different frequency ranges and different types of sensors. Or they may be 'frequency weighted' and give different results at different frequencies. Which meter is correct will probably depend on which side of the argument you're on....
Why does the reading almost disappear when I move just a few metres? EMFs spread out in many directions from a transmitting aerial (antenna) and generally reduce somewhere between the square and the cube of the distance from the meter to the source. If you are near a source such as a wireless router, the signal will reduce rapidly with distance.
Why do I get much higher readings in certain places? 'Hot spots' are quite common and are generally caused by EMFs being reflected, refracted or re-radiated by metal objects or building materials. Also, fields combined from several sources may 'add up' in some areas and 'cancel out' in others.
Why do readings taken very close to the source seem odd? Most meters are not able to function reliably in the 'near-field' close to the source. For microwave sources such as mobile phones, readings taken less than around 0,3 metres away will generally be inaccurate.
Which meter is best for finding ghosts? I don't know. Unfortunatley I've never (knowingly) met a ghost to test them on! I have no experience of paranormal investigations. Most investigators seem to favour ELF meters, and the lower the frequency response the better. Frequencies of only a few Hertz are generated naturally in our environment and in our bodies so this may be the best area to investigate. Also, a meter measuring voltage fields at these low frequencies may be more sensitive to very small changes in emfs.
Can an EMF meter measure the frequency of EMFs. No, most EMF meters are 'broadband' - they measure the total EMFs across a broad band of frequencies. It may be possible to measure the frequency of strong EMFs with a 'frequency sniffer', however these are generally not designed for digital signals. The usual instrument for measuring both frequency and strength of EMFs is the spectrum analyzer. This instrument measures across a broad band of frequencies a little at a time, storing and/or displaying results for each individual narrow band of frequencies. Spectrum analyzers are expensive, as a search on Ebay will quickly demonstrate! Some simple, inexpensive SA's can measure a limited band of frequencies such as audio (music) or wifi.