The Last Word – EMF

These are a selection of the letters received on the topic of EMF that were used as a basis for the Q & A article in the June 2021 RadCom.

EMF

Richard Benton, G4WKW

Most radio amateurs will have received their email from Ofcom, as I did on 3rd March. At the time of writing, I have started doing a spreadsheet with all my calculations and have been considering what changes I can make to lessen the risk of causing danger to others, as well as myself. I found the article on New Licence Regulations in March RadCom to be very informative, although obviously incomplete as things were still being clarified.

I am greatly concerned about this new requirement (not, that I think it is unnecessary). Only a tiny percentage of very fortunate radio amateurs may have their station set up in a remote location on a big farm, or in the grounds of a stately home, and the vast majority of people are much more limited. Having lived in rented accommodation for some years, the last one being a loft conversion with 4 skylights and no ability to use any outside aerials, it would seem people in that situation would find it virtually impossible to be compliant with the new regulations.

I was delighted to move into a retirement bungalow at the beginning of December with a garden front and back. I have set up three main antenna: a quad-band collinear with the base up about 5m, primarily for 4 and 6m, a dual-band collinear for 2m and 70cm and a coil-loaded end-fed long wire, as an inverted-L for 80m up to 10m. The vertical section of the long wire runs up a DX Commander pole, securely fastened to the side of my bungalow with strong brackets and wall-bolts. The problem is that a public footpath runs alongside of that side of my property, the other side of a wall, so it is possible for someone to stand on the footpath within 2 metres of the vertical section of my long wire.

In view of that, my only hope of compliance is the phase in your article under Stage 3 “…taking measures to ensure that no-one is present in high-exposure areas when transmitting”. I already have a ‘BirdCa’” streaming to the internet, which covers my bird feeders and the area around the end of the horizontal section of my long wire, so can easily monitor that. I am intending to set up another camera covering the side of the bungalow and footpath running alongside that, so that I can monitor live if anyone is getting close to my DX Commander, both before and during transmission. That in itself could be problematic though. I have seen guidance in the past that states that CCTV cameras should only cover your own property, although in my experience, the police are very happy to receive CCTV footage from recordings when a serious crime has been committed in an area. Perhaps different rules apply if one is not recording, only looking at live camera feed?

Although less of a risk than higher frequencies, how many people can hope to be compliant with 80m or top band? After been totally unable to use 80m from home for far too many years, it is a delight to be able to use it at my new home. I would be extremely sad to lose that ability, after only having just regained it again! I used to use 40m sometimes using an indoor mag loop in my last location, but decided that it was too dangerous to me, as well as neighbours, so stopped using it a long time ago.

As things stand I wonder if over three quarters of current radio amateurs will be classed as non-compliant?

 

John, G0UBE

I feel I must pass comment on this article and the issue of the change to our licence. In all RSGB communications we seem to be being sold the idea that this is not a problem. All examples are antennas up in the air so height aids with compliance. Not all operators have the luxury of masts and towers or long plots as keep being used in the example. The video to explain the calculator mention 6m heigh and 10m high. This is not possible in small urban plots where the only way to get on high bands is with wire antennas fed at ground level and run up over buildings. This put the separation zone in next-door neighbours gardens and the wire over the roof includes the upper floor of the house. On page 25 we have a nice ‘Suburban Garden’ that can house a 80m dipole. That’s 140 feet long! Try Suburban Garden 43 feet long. The RSGB needs to look at how many Members will be losing their hobby (in my case 30 years as RSGB Member) because these separation zones are a problem instead of focusing on cases that will work. Without 80, 40 and 30 I have no hobby, and 20m is the biggest dipole I could accommodate. I spent 8 months of 2020 while off work trying different antenna and an inverted L fed at the ground is the best.

 

Andrew, M0AQM

The article on EMF compliance in the latest RadCom was both timely, informative and raises a few questions in my mind:

1) To date the RSGB has not considered any ground mounted multi-band trap verticals (6-BTV etc) in their calculator. As there are no published gain numbers for my vertical, I am assuming its 0 and using a Custom option to reflect that? Some clarity on this in future articles / versions of the calculator would be useful. Definitely something for the pre-assessed library.

2) The ARRL has published tables in Chapter 28 of the ARRL handbook that seem to suggest amateurs should only really be concerned with power above or at 100W at HF (160-10m) frequencies. Interesting how different national organisations are reaching different conclusions based on the same ICNIRP standard. Perhaps this anomaly could be explained in a future article?

3) In the ARRL publication “EMF and You” on p192 onwards there are a number of charts for 1/4 wave ground mounted verticals. In these the safety levels vary from 1-4 feet for a controlled environment such as an amateur’s home at 100W (160-10m) depending on band. More manageable than the 4 meters odd the RSGB calculator shows for my installation – but which is a compliant distance – or are both ?

Given these discrepancies between national organisations and the uncertainly around frequencies below 10Mhz in the UK perhaps the only realistic option is to put up a 40ft tower – I wonder if the planning officers and partners will see it that way.

Steve Carter, G8EPA

Imagine for a moment a world in which Ofcom had hitherto issued amateur radio licences with no restrictions on the transmitted power levels. And then subsequently Ofcom came along and said now we are going to impose a new licence condition that sets the maximum power that you can use on every band. If that had happened, I suggest that we would be going through exactly the thought process that we are on EMF: How can I measure the power accurately? Can I build or buy a simple meter that will measure the power? Do I need to calibrate that regularly? Can I do a theoretical calculation of the power, or do I need to actually measure it? Do I need to install a device that will automatically prevent me from exceeding the power limit? Do I need to measure the power separately on every band and every frequency that I might ever operate on? How do I record the power that I am using? If I run very low power, do I still need to prove that I am under the limit? How are Ofcom going to check that I am operating within the limit? Will the planners or my neighbours be able to use the limit as a way of restricting or stopping my enjoyment of our hobby? 

Yet we accept the power limit without excessively worrying about it. So even if we dislike the imposition of the EMF limits, or think that the rules are not proportionate (a word that Ofcom are very keen on) relative to the potential problem, for most, to comply with the EMF condition will be trivial, just as it is with power limits. For a few who are operating at the edge of the envelope it may be more difficult to prove compliance, as it is difficult to guarantee compliance with the power limits if you are running the full legal power. But if you don’t have the technical competence or the measurement capability to demonstrate compliance then maybe you should take a step back from the edge of the envelope. For those of us who are interested in the theoretical and practical implementation of compliance with the EMF limits, or for anyone who is pushing the envelope, then the challenge of compliance is probably exactly the sort of reason that we are involved in the hobby.

 

Mike, GW1SXT

Having digested the new Ofcom EMF rules to be applied, it is surely a risk assessment for fellow radio amateurs to make. But it seems unless you got a lot of space to put up a HF antenna eg a G5RV or any wire antenna at a safe distance from the general public, it won’t work. How is Top Band a workable frequency anymore for someone with a small garden and boarders to other properties. VHF/UHF frequencies are ok at shorter field strengths so maybe more easy to apply but near fields to properties also must be assessed. It seems to me go to a calculator sheet tick the boxes and you are done. 

 

K J Maxted, GM4JMU

ICNIRP imposes some very severe exposure limits to the magnetic field component of the Radiofrequency field. The exposure graphs published for our guidance demonstrate a frequency dependence that makes the acceptable exposure limit decrease linearly towards 10MHz and then plateau out at a low level exposure limit. It is this frequency dependence that rings an alarm bell for me. And, if it is not clear at first sight, this low limit makes compliance in the near field which extends to several meters from the antenna a real problem.

I am a retired medical physicist and entered the profession because of my interest in the interaction of the human body with electricity and magnetism. Many of the imaging techniques that have elicited such advances in medical science depend on ionising and non-ionising radiation so I was very interested to explore how these ICNIRP exposure limits have come about.

I was particularly concerned to read in the WHO** publication, which embodies the science used for ICNIRP, that in consideration of the magnetic field, Faraday’s law of induction was stated as the foundation on which human tissue dosimetry is based. In essence they state that the induced current (in tissues) is proportional to the rate of change of the magnetic field, hence the direct frequency dependence. They state that although the electric field component decreases within the human body, being largely limited to the surface, the magnetic field (component) is unchanged and affects tissue within the entire volume. The resulting dosimetry and exposure limitation is based on computing a sum of VOXEL (volume elements) to come up with practical exposure limits.

The problem that arises is, can we ignore Maxwell’s equations entirely because the human body is a conductor (albeit a poor one)? Does the H field component exist in the absence of the E field? It would have surprising effects of our understanding of skin depth  for instance if this were the case. Ask the question why we have to use extremely low frequencies to communicate with submerged submarines. If the magnetic component of the Poynting vector penetrated the sea in isolation we would be able to receive signals at any frequency in a submerged submarine using a loop antenna to pick up the magnetic field component.

The whole of the magnetic field dosimetry on ICNIRP depends on this premise of frequency dependence resulting from use of Faraday’s law. If we did not have this then the exposure limit would remain at the maximum limit drawn as the upper horizontal line on the left hand side of the published (Ofcom) exposure graph. I wonder if considerations that reasonably apply for 50 or 60Hz power line fields can be extrapolated this way? A century ago the HF spectrum we use was considered useless except for experimenters. Has this mentality prevailed again in the scientific community responsible for these regulations and we have been caught between the low frequency spectrum that does have some physical effect on the body and the VHF to microwave region that has undeniable heating effects? I am of the opinion that the science here is wrong and that we are being subjected to complying with an unreasonably low exposure limit in the low to medium frequency HF spectrum.

 

Peter Garnett, G4LZJ

I have read with dismay about the expected new regulations relating to EMF. I was first licensed as a G8 in the mid 70s and found my intermittent use of amateur radio very pleasant. Unfortunately, I am beginning to wonder how long it can last as a hobby. We amateurs have had to take and pass examinations, which are extremely elementary, to allow us to operate. In my time I have built simple radios and successfully used them but the norm now seems to be to purchase expensive equipment the cost often outside the reach of the average amateur. 

Regarding the probable new guide lines the technicalities will be enormous and the associated graphs and mathematics well beyond the reach of most amateurs. 

As a retired professional statutory inspection engineer, I have often had to be involved with ionising radiation and it’s safe use was quite involved. It was quite possible with the correct mathematical ability to calculate safe distances from any ionising source coupled with the surrounding geography. Owing to the complexity of the theory the solution was to use radiation monitors and dosimeters plus discussions with the radiological society and regular updating courses. 

I have a suspicion that the new EMF regulations will be as involved and EMF detectors will have to be used giving an extra cost to the station equipment. I have been to many meetings where so called experts have pontificated with their narrow focused knowledge and in many cases where the science has been correct but the social implications have been ignored. I have found that the most important question to ask in any discussion is WHY and hope that the RSGB uses this simple word when discussing the need for these regulations in amateur radio.

My main use of amateur radio is to rag chew, I have no interest in contests or circuit diagrams nor do I wish to read any technical articles.

For me amateur radio is a pleasant pastime, a hobby, and that is what it is, in its basic use there is no need for advanced technical information. I am in my late 70s and have no intention of studying additional  criteria to keep my license. If I am required to do so I will simply close my station down and get on with other things.

I hope the RSGB will prevent that happening by not only being involved in discussion but also question the need for these regulations in respect of amateur radio.

Category: The Last Word