Investigation Levels for UK Amateur Radio

This is a summary of the Board’s guidance on exposure to electromagnetic fields as applicable to those frequencies authorised for use by amateur radio stations in the UK, as referred to in the Radiocommunication Agency’s Amateur Radio Licence Terms, Provisions and Limitations booklet BR68. Underlying this guidance are basic restrictions on exposure, based on energy absorption rate and induced currents in the body. The investigation levels shown below are a set of field strengths and power density values below which the basic restrictions on exposure will not be exceeded. These investigation levels are not limits on exposure, but compliance with them will ensure compliance with the basic restrictions. Exceeding them does not necessarily mean that the basic restrictions have been exceeded. However, it does mean that the exposure situation should be investigated further to assess compliance with basic restrictions.

Band	Frequency	Electric Field Strength V m-1	Magnetic Field Strength A m-1	Power Density W m-2
LF	135.7–137.8 kHz	1000	64	–
160 m	1.810–2.000 MHz	316	5	–
80 m	3.500–3.800 MHz	164	1.35	–
40 m	7.000–7.100 MHz	85	0.36	–
30 m	10.100–10.150 MHz	59	0.175	–
20 m	14.000–14.350 MHz	50	0.13	6.6
17 m	18.068–18.168 MHz	50	0.13	6.6
15 m	21.000–21.450 MHz	50	0.13	6.6
12 m	24.890–24.990 MHz	50	0.13	6.6
10 m	28.000–29.700 MHz	50	0.13	6.6
6 m	50.00–52.00 MHz	50	0.13	6.6
4 m	70.00–70.50 MHz	50	0.13	6.6
2 m	144–146 MHz	50	0.13	6.6
70 cm	430–440 MHz	100	0.26	26
23 cm	1240–1325 MHz	160	0.42	67
13 cm and above	2310–2450 MHz and all higher bands	194	0.62	100

Notes

Where values are frequency dependent, the mid-band value is used. The differences due to frequency variation within a band are negligible.

More detailed information is available in the booklet Restrictions on Exposure to Static and Time-varying Electromagnetic Fields, available on request from NRPB.

There is an investigation level of 20 mA for contact current (current flowing through a person when a metallic object is touched) for the frequency range 70 kHz–100 MHz.

For all exposures below 12 MHz, both the electric and magnetic field components must be measured and compared with the relevant investigation level. At frequencies above 12 MHz, when in the far-field, either the electric or magnetic field component may be measured and compared with the investigation level.

As the basic restrictions on exposure above 10 MHz are time-averaged, exposures can also be time-averaged when comparing them with the investigation levels. For the frequency range 10 MHz–10 GHz, it would be appropriate to average the exposure over any 6 minute period. To do this field strength exposure values must be converted to power densities and the averaging applied to the resultant power density. For amateur bands above 10 GHz, the averaging time should be reduced according to the formula 68/f^1.05 minutes, where f is the frequency in GHz. For example, the averaging time for 24 GHz is 2.4 minutes, and 1.2 minutes for 47 GHz.

September 1999

Last updated 10th September 1999