Instruments
The value of a good quality EMR meter cannot be overstated, particularly when seeking to quantify the effectiveness of any implemented preventative strategy. For power grid wiring and connected appliances, “gauss meters” are available from online sellers beginning at under $50 USD.
On the other hand, a dedicated meter is required to measure the higher spectrum of radio frequencies (RF) emitted by mobile phones and other wireless technologies. The TriField or Cornet instruments are popular and cost-effective choices beginning at around $250. As a compromise, a number of products incorporate both functions in a single package.
Unless a particular meter is specified as tri-axial or omni-directional, its maximum sensitivity will most often be aligned upon a single axis. This can be demonstrated by rotating the meter 90 degrees on its horizontal and then vertical axis while observing corresponding variations in the numerical display. Apart from capturing the highest possible reading, this technique can also assist with visualizing the topology or polarization of the incident electromagnetic waves.
Depending upon type, meters provide readouts according to various units of measurement. To avoid confusion, consult the chart below, or an online converter such as this Field Strength Calculator.
Direction Finding
Unlike the diffuse propagation of low frequency radiation, microwaves tend to be directional or quasi beam-like. Unless an RF meter comes equipped with a directional antenna (as shown above), an improvised method must be employed to isolate the source of an incoming signal. While keeping the meter’s display visible, hold it flat against a large baking tray, or similar metal sheet. Signals will then be blocked from the direction you are facing.
With both arms outstretched, slowly rotate your body, meter and tray in unison full circle while noting the point at which the highest reading is obtained This indicates that the strongest incoming signal is at your back. If no significantly higher reading is occurs at any single point during rotation, multiple signals are most likely arriving from different directions. This necessitates a true directional meter. Otherwise, microwaves may be inadvertently concentrated by any subsequent shielding instead of being reflected away.
Spectrum Analysis
Any transmitted signal is defined not only by intensity values but also the frequency with which the most predominant ones occur. This can be the 60 cycles per second of the commercial power grid to billions of cycles per second in the case of mobile phone and other microwave networks. To measure this parameter a spectrum analyzer is required. It graphically shows intensity peaks across a nominated range of frequencies, or “bandwidth”. In a relatively expensive class of device, the product below is an unusually cost-effective choice. Here is a video of it in operation. The price has increased since then to a few hundred dollars depending on model.
Low Cost Options
This technique requiring only a cheap AM radio is best suited to informal demonstrations. Using an AM Radio to Detect EMI – YouTube
The following free or trial software creates a graphical display of active Wi-Fi networks and their relative signal strengths. Measurements require your computer’s Wi-Fi facility to be enabled. Afterward, it can once again be switched off.
Ekahau Heatmapper
inSSIDer Lite
NetSurveyor
NetSpot
Refer to the Galleries page to view a variety of instruments and methods in actual use.