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EMF UK - EMF Meters and Surveys for homes and businesses

Help and Advice

EMF meter buying guide

This section attempts to explain the basics of EMF meter selection. There is a short explanation of generally used terms and requirements followed by an easy to use selection chart, a glossary of terms and some FAQs.

Thinking of buying an EMF meter? The wide range of EMF meters available can make this a difficult decision. 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
315MHz, 380MHz, 433MHz, 458MHz, 868MHz and 915MHz Remote control, telemetry, AMR ('Smart meters')
380MHz to 400MHz TETRA digital radio
446MHz PMR446 personal 2-way radio
470MHz to 854MHz Television broadcasts
800, 900, 1800 and 2100MHz Mobile phones, AMR ('Smart meters')
1.9GHz (1900MHz) cordless DECT phones
2.4GHZ to 2.5GHz wifi (wireless-b, -g and -n), bluetooth, wireless cameras, video senders, RC models, AMR, mice, doorbells...
2.45GHz microwave ovens
5.15GHz to 5.85GHz wifi (wireless-a and -n), wireless cameras, video senders 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, preferably, 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. EMF meters may have a single measurement range or they may combine several ranges in one instrument.

The next thing to consider is the sensitivity of the meter. Most ELF meters measure the magnetic field in Tesla or alternatively Gauss. Since household values are normally low, these would normally be expressed as uT (millionths of a Tesla) or mG (thousandths of a Gauss). Typical background household ELF EMFs are below 0.2 uT (or  2 mG - 1 mG is equivalent to 0.1 uT) and for most people a meter measuring from 0.1 uT to at least 2 uT is adequate for home or office surveys. However, anybody who has been diagnosed as electrosensitive will need a more sensitive EMF meter with ranges for ELF electric fields. For testing the fields directly under overhead power lines a meter measuring up to at least 20 uT and 2000 V/m 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 (microwatts per square metre), or mW/m2 (milliwatts per square metre). Some older instruments and microwave oven testers use uW/cm2, or mW/cm2 - these /cm2 units are 10,000 times larger than /m2 units and it is important to be aware of this. For home or office use we would ideally like a meter that measures down to 1uW/m2 or less. 

The following table summarizes the suitability of our various meters and antennas for measuring common EMFs found in most homes:

 

Glossary:

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
Electrosmog- 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.

FAQ's:

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 slowly twist the meter about; the actual field strength will be between 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; use a RF or combined meter.

Can I measure the field from powerlines with a RF meter? No, you cannot; use an ELF or combined meter.

Can I measure both mobile phone mast signals and the field from powerlines with a 'dual mode', 'combined' or 'ELF/RF' Meter? Yes, you can.

Which is your most popular meter? The ED78S is our most popular meter - it covers almost all EMFs found in most homes.

Why does my RF meter give different results to someone else's? Formerly, when there were just analogue signals, and not many of them, it was relatively easy to measure the average or peak strength of 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. Older meters, or meters from different manufactures, may calculate this differently. Also, the meters may have different frequency ranges and/or different types of sensors. A few meters are '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 my ELF meter give different results to someone else's? 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.

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 low intensity source such as a wireless router, the signal will reduce rapidly with distance. If far away from a strong source such as a mobile phone mast, the signal will reduce more slowly. This can be useful in estimating where the source of the EMF is located.

Why do I get much higher readings in certain places? 'Hot spots' are quite common at higher frequencies 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. We do however supply the ED85EXS and MP-1 probe for near field work.

Can an EMF meter measure the frequency of EMFs? Most EMF meters are 'broadband' - they measure the total EMFs across a broad band of frequencies. However meters are available which will display the frequency of the strongest source. Formerly this was limited to continuous wave signals, however it is now also possible to measure the frequency of pulsed signals such as wifi; our MD18 is a digital frequency meter of this type.

How do I measure individual EMFs? It is possible to measure individual EMFs by filtering out the unwanted ones, ideally leaving just a narrow band of frequencies. The preferred instrument for measuring both frequency and strength of individual 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 can be very expensive, as a search on the Internet will quickly demonstrate! Nevertheless, simple, inexpensive SA's have recently become available; see our RF Explorer for example.

Can I record and download my results? Unfortunately data logging facilities add significantly to the price of an instrument. For recording and downloading ELF EMFs we have the TM-192D. For comprehensive recording, downloading and presentation of both ELF, RF and microwave EMFs we have the FA735 Field Analyser.

Why all the fuss about magnetic fields; hasn't the earth's own magnetic field has been around throughout human existence? Yes it has, however it is a static field and cannot induce voltages inside our bodies in the way that man made EMFs (which are alternating fields) can. Very large static magnetic fields can nevertheless cause problems, with some medical implants for example. EMF UK can supply the HT-201 for large static and ELF field measurement.

Which meter is best for finding ghosts? I don't know. Unfortunately 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.

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