V/m 2
Station
testing forms part of the licence conditions that as amateurs we are
required to conduct. I don't have oodles of test equipment, but can
conduct some simple tests using the two radios I have, my SWR &
Power meter and my dummy load. Using these items gives me a good idea
of actual power output, frequency accuracy & cross-band
interference. I am also aware that I need to be mindful of RF exposure
given that I am able to run legal limit using my valve amplifier. With
that in mind, here are estimated safe power levels I can use based on
max allowed electrical field strength figures when using my multi-band doublet.
Given that I run less than 400 watts, I know that the
RF exposure that my station generates falls well within the Health
Protection Agency and soon to be UK Ofcom guidelines. I am pleased that I have been able to
document this information!
DB gain as per NEC antenna modelling based on the dipole with its' centre at 40ft and the ends sloping down to 20ft. Max permitted UK power used to generate figures. You will note that on 10m my max power output has been lowered to not exceed 250 watts, this is to maintain a distance of 20ft away from the end leg of the doublet.
The table below relates to using a doublet in an inverted V configuration with the apex around 40ft, the doublet is in free space. Its usually only on 80m that I run close to full UK leagl power and from the results below I know my safety levels are sound and will comply with Ofcom requirements.
A useful website to calculate EMF can be found here http://hintlink.com/power_density_uk.htm - you will need to have some idea of the gain of your antenna.
HF Calculations as of 18/10/2020
VHF/UHF Calculations as of 18/10/2020 (my colinear on top of the chimney)
Calculation Results
Max Average Power at the Antenna
50 watts
Antenna Gain in dBi
5.5 dBi
Distance to the Area of Interest
20 feet
6.096 metres
Frequency of Operation
443.125 MHz
Are Ground Reflections Calculated?
Yes
Estimated RF Power Density
0.0973 mW/cm2
Maximum Permissible Exposure (MPE)
1.4821 mW/cm2 Controlled environment
0.3004 mW/cm2 Uncontrolled environment
Distance to Compliance From Centre of Antenna
5.182 feet Controlled environment
1.5795 metres
11.5254 feet Uncontrolled environment
3.5129 metres
Does the Area of Interest Appear to be in Compliance?
yes