Electro Magnetic field Exposure, OFCOM & RSGB

[trh01uk]

Originally Posted by G3PIJpeter

Let's look at a piece of wire on the HF bands and have a go at a few more numbers.

The effects of RF fields at HF are much less well established than the basic heating effect (mugs of cocoa in waveguides in 1945) but there is some statistical evidence about influences on cell membrane permeability at a biochemical level. The IEEE paper at http://emfguide.itu.int/pdfs/C95.1-2005.pdf contains (Table 9 page 25) the usual sort of guidelines for uncontrolled exposure at 3-30 MHz i.e.

Electric field strength = 823.8 / f (volts/metre)

Magnetic field strength = 16.3 / f (amps / metre)

RMS power density = 1800 / f^2 (watts / square metre)

So how do we interpret these figures for 400 watts into a low half-wave dipole or an end-fed wire? My intuitive (but likely faulty) reasoning runs as follows.

The close-up field strength depends on the current in the aerial wire and the value of this current varies inversely to the voltage as we move towards the end of the wire: electric field strength goes up as magnetic field strength goes down, roughly maintaining watts (power density) as amps x volts . . . (?) However, 400 watts into a half-wave of wire (136 feet at 3.5 MHz) is not all going to be concentrated at the spot where you are standing. The inverse square law says that intensity decreases with the square of your distance from each segment of the aerial. I suppose that you could cut the aerial wire into an infinite number of segments and use calculus to sum the intensity at wherever you are standing. That’s where the exposure guides come in.

Risk: 10 people are currently dying each day from Covid-19 while 30 people are dying each day from prostate cancer and 30 from breast cancer. 1500 people a year die in road ‘accidents’. The causes in these cases are clear. The case for a causal connection between any specific illness and HF RF is not clear and, so far as I know, any specific effect has yet to be demonstrated. There are some statistical correlations but sources conflict. 400 years ago, we’d be burning people at the stake for putting wires up in the air - let’s hope at the very least that we are spared this fate.

- Peter

Peter,

thank you for giving another worked example. Its worth noting (perhaps!) that the E-field equation you give works out at 28V/M if you are in the 10m band at 29MHz. And then referring to that table you reference, that figure of around 28V/m carries on up (as a constant) to 400MHz. The reasoning here is that we are getting to "full body resonance" where the wavelength is similar to body dimensions (particularly height I guess), and thus any effect might be amplified by resonance.

That figure is meaningful for me, because I used to be in charge of EMC testing at Racal Security (many decades ago), and we used to test all products for immunity to a modulated field with a peak FS of 20V/m. In those days, that was essentially to protect from false alarms to "realistic fields from mobile/portable radios". That would be amateur radio, taxis, police etc at the time. And the products would be in the normal business/domestic environment, which suggests that humans could be exposed to similar fields, I suppose.

While I agree with you that the risks here are absurdly low in the context of Covid, etc, the civil servants who have to enforce this stuff will most likely not understand any of it. These will just be numbers to them. They will farm out measurements to some specialist company no doubt and then act on any report received. Amateurs beware I suggest!

Richard

[CambridgeWorks]

Even if we are nowhere near the maximum level, I fear the easy option is the onus would be for the amateur to prove the actual level.
No doubt China will provide a CE marked piece of kit of dubious accuracy.
Rob

[woodchips]

Read this with interest. Not because I belong to the RSGB or transmit radio signals, but as another example of mission creep.

I have just had a paper from Confor about woodlands, diversity and forestry, I have a small wood. The paper is 36 pages long and has 149 references. Reading the paper and the references there seems to be a whole swath of the population that creates woe is me papers at universities and similar institutions. They seem to have to do something to justify their MSc's and positions so finding something that reads well on the internet is essential.

Seems radio emissions is another one.

Good luck. Fighting this sort of doom, gloom and disaster story is impossible, you will end up being regulated out of existence. Other examples if you want to read it up are the SuDS surface drainage legislation, or the Waste Carrier's Licence.

We are just a few years away from being legislated out of existence.

[ms660]

All amateur radio transmissions should be limited to 10 watts.

Lawrence.

[marty_ell]

Originally Posted by dsergeant

As for 5G, having just encountered a couple of the anti-5G crowd on a different forum it is impossible to reason with them, they can't seem to understand the truth.

Originally Posted by Radio Wrangler

We had an anti-cellphone mast protest in out village years ago. It was quite remarkable to see the number of protesters holding phone handsets to their ears.... especially the kids!
David

Back when 4G was being introduced, providers wanted to put a small repeater mast in our village (not just for 4G but back as far as 2G!). It happened to coincide with the parish meeting at which I was asked to comment, being the only technical non-incompetent in the village. Despite my polite explanations, repeated many times slowly and simply, and despite the application sketch showing a neat and inconspicuous installation, the meeting decided by 100%-1 to reject the application.

Needless to say, in all the years since there has been the constant complaint at the lack of mobile signal in the village.

Always remember - the incompetents or the 'can't be bothered to find out' brigade have always vastly outnumbered us. I simply ignore them; when the lack of something useful causes enough people inconvenience, somehow the attitude changes overnight.

Perhaps we will soon see PRO-cellular protests in our village!
Cheers, Marty

[turretslug]

I wonder were they equally unanimous in their rejection of microwave ovens and induction hobs.

[Refugee]

The worst problem I have found with phone masts is the disruption caused by upgrades.
There is one by a "T" junction not far from where I live.
Every time there is a new "G" they put up traffic lights and dig up the road.
It has caused the road to get excavitus caused by back hoe virus.
The things need to be sited where there is good vehicle and cable access.

[GMB]

One of the less obvious ways to exceed the limits is running 50W from a car using an aerial with a bit of gain, e.g. a 5/8. This could get you over 60V/m standing by the car. If you were running a cross-band repeater (as many do at events) and the net was busy then this could exceed the limits.

But in the recent OCFOM consultation, the big issue was not about exposure limits at all as these have always been a requirement - perhaps some people had forgotten that. The onerous new thing was the requirement to have on file the assessment/measurements of every configuration used. It hits amateur radio much harder than phone masts.

If the proposal becomes law (has it yet?) it means that instead of being convicted for exposing someone to dangerous radiation, you can be convicted for not having the right paperwork!

[Refugee]

Much vehicle based equipment is illegally boosted in order to get the range out to other drivers to warn of traffic jams.
As traffic jams have got longer the sale of illegal boosters as increased accordingly.
Mobile phones are too fiddly and cause too many accidents.

[Radio Wrangler]

The phone base stations nearest work are regularly updated without any protests. They are right beside the road amongst some light bushes right before the roundabout at the entry to Heriot-Watt university. The uni has a good crop of wealthy students from all over the world, and a number of them have been provided by their family with some rather potent transportation. At least once a year someone or another drives into the cabinets and smashes them off their foundations, crushing the internals. It isn't anti phone mast activity because if you look at the streetlamps around there, and the signs, they also bear the marks (and several are now missing or leaning at a foppish angle) The control cabinet for the traffic cameras got relocated underground after two incidents!

It isn't entirely the students... the driver testing centre is just up the road, so all the driving instructors cover the area intensively.

However, the poor little cabinets of electronics bear the consequences and get regularly bluto'ed.

David

[Refugee]

It sounds like the vehicle access to the Scottish masts it a little bit too good.
The one near me does not even need a physical visit to see the disruption.
https://www.google.com/maps/@53.2730...7i13312!8i6656

[GrimJosef]

Originally Posted by GMB

... If the proposal becomes law (has it yet?) it means ... you can be convicted for not having the right paperwork!

True in very many areas, and has been for a while. There's a sort-of reverse version too. I went on a training course once for some new H&S issue (can't remember which - maybe COSHH ? PPE ? DSE ?) and the trainer impressed on us how important it was to have the relevant risk assessment carried out and on file. Even if it was hard to generate a realistic document we should at least make sure we'd done something. There had already been a few HSE interventions against organisations whose staff had actually come to some sort of harm or other, or had at least complained of problems. Up to that point not one employer who had done a risk assessment, no matter how incompetently, had been proceeded against by HSE. But most of the ones who were behind with the paperwork, even if they were trying their best in the actual workplace, had been hauled over the coals.

Cheers,

GJ

[Radio Wrangler]

The risk assessment for filling in the risk assessment needs to cover stabbing oneself accidentally with the pen, for paper copies, or eyesight damage from an improperly sited screen on the desk or an improperly adjusted chair.

David

[GrimJosef]

If you're doing the risk assessment at work then indeed it does. Here's the HSE's guidance on DSE assessments https://www.hse.gov.uk/msd/dse/assessment.htm. But now we're going OT.

Cheers,

GJ

[AC/HL]

You do risk assessments unthinking every time you do anything. The hard part is writing it down, as it always sounds petty to yourself. To someone with absolutely no experience, and an open mind, it's the difference between chance and certainty.

Originally Posted by merlinmaxwell View Post
I do wonder why and how they reached those figures.

I still standby why those figures, thumb, plumb and pie I think.

[Electronpusher0]

Originally Posted by Radio Wrangler

The risk assessment for filling in the risk assessment needs to cover stabbing oneself accidentally with the pen, for paper copies, or eyesight damage from an improperly sited screen on the desk or an improperly adjusted chair.

David

Not a joke, ref The Health and Safety (Display Screen Equipment) Regulations 1992 & Directive 90/270/EEC of 29 May 1990

See risk assessment attached.......

Part of my previous life.

Peter

[M0AFJ, Tim]

Originally Posted by ms660

All amateur radio transmissions should be limited to 10 watts.

Lawrence.

If that was the case I’d hardly ever get a V/UHF signal out of Helston!

[ms660]

Must admit I never much saw the point of VHF ham radio. Across the world with 10 watts with a home brew rig then yes, high power squawk boxes, never saw the point in them, but hey ho.

Lawrence.

[Radio Wrangler]

Yes I knew about screen regulations etc.

Fortunately, the risk assessment for filing in the risk assessment of filling in the risk assessment of some task is the same as the risk assessment of filling in any risk assessment!

So although the "there must be a risk assessment for all activities" imperative kicks off a limitless recursive series, at least the texts converge and once one is written for the second iteration, it can be submitted as an infinite number of copies, and that will cover you for everything.

David