Articles‎ > ‎

ICNIRP compliance software

UPDATE 14 May 2020 - ICNIRP have released a new version of their Guidelines. These appear to require a more complex measure of compliance for LF/HF as all exposures must be treated as if they are in the near-field of the antenna, even if in fact they are in the far-field. The result is that both electric E-field and magnetic H-field measurements must be within specified limits. This appears to mean that existing software, such as described below, will no longer be adequate. It also suggests that any measurements will be more difficult to make and may require two sets of equipment. 

Original article:

The public interest in potential of risks from exposure to RF fields has been increasing recently (largely I suspect due to fake news about 5G). At the time of writing (Mar 2020) Ofcom are consulting on whether to make compliance with RF Exposure Guidelines from the International Committee for Non-Ionizing Radiation Protection (ICNIRP) a licence condition for all Wireless Telegraphy licences. Licensees would have to keep records of measurements and calculations showing compliance. This proposal appears to include amateur licences as well as those for broadcast transmitters and mobile base stations. The ICNIRP Guidelines are not easy reading nor do they cover measurement methods, so amateurs may find it a challenge to document their compliance. The Guidelines are under review, with a draft published in 2018, and may change soon.

The US FCC set similar exposure limits back in 1999. Although these are like the ICNIRPs they appear far easier to document and comply with. The ARRL provides support and easy-to-use forms for their members. 


ICNIRPcalc

German amateurs have had to comply with a fairly rigorous system for compliance with EMF rules including ICNIRP's Guidelines for many years. In their case they have to submit plans of their property and antennas as well as field calculations to the relevant ministry. The DARC, the German equivalent of the RSGB makes several programs available to help members fulfil this obligation. DL9KCE, the author of one - QuickWatt - has made this slightly simplified version ICNIRPcalc available free via the IARU. You can download it from the IARU website here. There is no need to install it - just unzip the download and run IcnirpCalc.exe. Other German software is available including Watt32, which seems to be co-written with the same author. The website for that is in German. The program is available to buy (on CD) but there appears to be no online shop.


ICNIRPcalc screenshot

The program was obviously written in German originally but seems to run in English by default. It has a few typos and German words, particularly in the antennas list. Another thing to note is the use of commas instead of decimal points in frequencies, gains & power levels. The program comes with a very useful pdf help file.

You use the software by entering the amateur band under consideration and your transmitter power output. Then, using three tabs, you choose/input the following:

your antenna

the operating mode and the number of minutes you would transmit during a 6 minute window (NB ICNIRP also talk about a 30 min window, which may apply).

your feeder and any other losses

for some antenna types eg VHF beams an 'Angle' tab appears, in which you enter the polarisation and height. You can also open plots of the beam pattern and safety zone. 

The antenna list is categorised by manufacturer but the first one on the list is ‘Allgemein’, which is a ‘general’ category. That is where simpler antennas like Big Wheels, dipoles, loops, slopers, simple verticals and long wires (Langdraht) are listed. I suspect antennas described like ‘Draht 2x15m’ (Wire 2x15m) are doublets, in that particular case each wire being 15m long.


Antenna characteristics

The field generated by an antenna depends on its gain and polar diagram. Data on many, many antennas is held in a text file which is read by ICNIRPcalc. The information on some of these includes the gain every 10 degrees away from the centre of the main lobe, which means the program can take account the reduction in field strength below beam antennas for example. The additional data is held in a separate text file and it is possible to manually edit the file to add missing data if you have it eg from a manufacturer’s gain chart or by modelling an antenna in mmana-gal or similar. There is a feature that lets you add your own antenna via a menu but it is a simple facility that doesn’t directly allow you to input the off-axis antenna characteristics.


Operating mode selection

Your operating mode determines the average power during the TX period. FM is full power all the time, SSB rarely is. The DTX setting appears to be for digital modes. (Don't be misled by the fact your transmitter is set to USB. The audio going to the transmitter from digital software like WSJT-X and HRD is not peaky like voice - it keeps the TX power constant during transmit period.)

 

Near field/far field

The program results in display of two distances, one in a green box for which is the safety zone and one in pink marked ‘nearfield conds’. (The fields radiating from an antenna only combine into a regular radio signals in the ‘far field’ of the antenna. Electric and magnetic fields in the ‘nearfield’ are far more variable and not necessarily in phase.) The need for the second box isn't immediately obvious.

The help file is in English but the relevant section doesn’t seem to have been well translated. It says “Now you finished all the inputs an you can look at the box in the lower left corner, where you will find the required safety distance in the green field. Since the calculations are all done assuming far field conditions, in the pink field the distance to which the near field reaches is given. According to German law measuring or near field calculations have to be used beside the here calculated far field solution, if the near field conditions apply outside the ham operators property”. 

The value in the pink box doesn’t seem to vary with antenna type as you might expect it to. I think that means the pink box simply shows how far you need to consider the near field extends rather than being a usable safety zone distance or a definition of where the far field starts. It seems to flag potential issues for bands from about 10MHz down. Unfortunately there is no guidance on measuring or calculating field strengths in the nearfield. One thing I can tell you is that buying a set of measuring equipment as used by Ofcom would cost you £15,500. Secondhand. Plus VAT!

Further reading:

Initial RSGB briefing on Ofcom consultation

Current ICNIRP Guidelines (note that ICNIRP call 100kHz to 300 GHz 'HF'!)

ICNIRP re the draft guidelines

ARRL information including a book, RF Exposure and You 


73

Mike
G4RAA

 

Comments