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Ofcom EMF risk assessment & UK SOTA

Hi Brian

That’s not a bad idea. I’m within the safe OFCOM separation distance here to my neighbours using the RSGB Spreadsheet on the 20m to 6m bands at 450 watts CW from the TX up to 6m and at 150 watts on 4m. On the 2m band where I have 50 watts into a 7 element Yagi I am also well within the OFCOM separation distance. I don’t have more power than that on 2m but I also calculated that if I ran 400 watts and did not include a -3 dB sidelobe loss I would likely be in breach of the OFCOM separation distance to one neighbours bedroom. Whether OFCOM accept sidelobe loss is unclear at this stage, although the RSGB include it in their spreadsheet and the author of the spreadsheet tells me when I enquired that -3 dB is the minimum attenuation that could be entered.

On bands below 20m I need to perform near field calculations I believe, so as you are doing, I plan to wait until the pre-calculated spreadsheet or some other tools provided by the RSGB are finalised.

Andy is right about my vexatious neighbours, who could have been likened to a lynching party when I faced up to them at a Town Council planning meeting last year! They weren’t impressed when my planning application for a Hexbeam was passed unanimously at an online virtual District Council planning meeting a few weeks later. I feel the only way OFCOM are likely to investigate EMF safe limits on amateur radio stations is when they have to because of complaints from neighbours trying to get aerials or masts removed from amateurs gardens and houses.

I don’t see anything to fear from this extra burden of regulation on activators, although we may be asked to display this sign a safe distance from the antenna.

73 Phil

Could you ask your neighbours to put that sign up in their bedroom Phil? That would cover you.

Perhaps mandate application of that sticker on the back of every mobile phone :grin:

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If some enterprising company were to make the warning sign into a flag pennant, I could fly one from the top of my 2m RH-770 whip - the danger being curious short-sighted onlookers might walk right up to it to read what it says.

It’s pronounced “Frankensteen”

A 3-page article on this topic in the March ed. of RadCom [first in a series of articles] adds some interesting details. Experts in RSGB and ARRL are sharing technical info and experiences as well as working with their national regulators (Ofcom and FCC).

It also says the EMF regulations are being driven by new telecoms. I suspect the ubiquitous and 24/7 nature of 4G and 5G, WIFI, Bluetooth, etc has raised concerns. By contrast, the relatively small number of amateur transmitters in the world, their highly discontinuous operation [i.e. mainly switched off 24/7], and their typical siting with respect to the public were not the likely impetus for the new regulations.

I’m confident Ofcom will be satisfied by the RSGB efforts to provide the vast majority of UK amateurs with pre-calculated examples of amateur station setups and customizable spreadsheets. Today’s UK regulator is even more hands-off than when I was first licensed in the late 1960s. I wonder if anyone gets a random notice of inspection nowadays.

OfCom have bigger fish to fry so I won’t be looking over my shoulder next time I’m activating Helvellyn. And if the Ofcom helicopter does swoop down beside my dipole, I’ll have that bit of paper at home to send them.

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Should the helicopter swoop, you can always say that the paper blew away. That’s my go-to excuse.

Hah! We’ll have to wait and see but I’ll be very surprised if it would be a requirement to carry the ‘proof’ with you in a portable situation. After all, we’re not required to carry our radio license. We have a peace-time culture in the UK not to have carry papers on us but provide them later if requested.

Would it make sense to push for an exemption below a certain power level? Since things generally need to be below 10w to get rated for human carriage (depending on antenna and duty cycle), then perhaps a case can be made for the presumption of safety.
73 de OE6FEG

It is possible to breach the limits by using a high-gain antenna even with QRP. Obviously this is more of an issue at higher frequencies. But for sure some specific example configurations can yield a table of guidance power limits, which under /P conditions we will mostly see as quite high.

Whilst a gain antenna can exceed the limits, would it not still be useful to have an exception for isotropic gain? After all, the limits for the 60m band specify “isotropic” gain, so an EMF risk exemption specifying “isotropic” gain is clearly possible. I wonder what proportion of activations actually use gain antennas? A very small proportion overall I suspect. A defacto exemption would still be useful to a very large number of portable operators; and not just in SOTA.
73 Matt

ALL of mine do. sometimes quite large gain.

None of mine do unless you believe that there is gain from a HF or VHF dipole. “No wind vane effect” either!

I wonder if we’ll see some ready made samples for common scenarios. How many of us use Inverted V on HF for example?

It seems the problem at portable QRP power levels is the near field, not the far field. Safety distances on the spread sheet come out quite small, but the Near Field Zone is larger. Do we just say we’ll use the Near Field Zone and not do further calculation? So I think it was for 14MHz 5W into a dipole we just make sure no general public within 4m when we transmit? Even though the far field safe distance was about 30cm?

I note that people can walk around with handies at 5W. They are used commercially. These things are next to the user’s head but are accepted. So I’ve assumed my SOTA setups safe as long as the elements were above head height. Though was there an exemption for less than 10W EIRP? So my MTR3B may be inherently safe, but if I take the KX3 or something bigger that can produce more power I need to do the maths?

I didn’t see the near field calculation - is there a spreadsheet or online calculator? I think this might be quite hard! And I’m not sure that the near field is centred at the feed point of a inverted v ( for example ) but might be the ends of a dipole - which in my case for SOTA are 1m or so off the ground attached to a walking pole. It could be that lonely summits are required for LF operations!
Can anyone cast a light on the near field calculations?

Ofcom published a revised proposed licence condition and guidance yesterday. From my interpreation it appears the calculator only works above 10MHz and beyond lambda/2*pi which could make life interesting.

Also the condition appears to apply to the power levels permitted by the licence, not that available from the equipment in use which presumably brings all amateurs into it’s purview regardless.

I’d be very glad if someone can show me I’m wrong…

73 de Paul G4MD

Handhelds and mobile phones operate at VHF and UHF of course where it seems you have only the heating effect to worry about.

The article in this month’s RadCom [see my post #86 above] says that you have an additional problem at frequencies around 10MHz and below: the A.C. currents and induced voltages in the human body from the RF [because they become resonant with limbs and organs at those frequencies] may be harmful even for relatively short duration and therefore require more restrictions on exposure that at much higher frequencies.

Actually, looking at the graph of E and M field strengths vs. frequency in the article, the safe thresholds for both are low in the VHF range and start rising as you go down in frequency below 30MHz.

The idea that a body that’s between say, 1.5 and 2 metres long can be resonant on a wavelength of 30m is a new concept to me.

Andrew, re-reading the article, I may have been mixing up two effects 1) the human body resonance problem in the lower VHF range [30-400MHz] and 2) the electrical nerve pathway problem [below 30MHz] which can affect the body’s internal signalling.

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OK - makes sense. Thanks. Next: how “safe” for EMR rating are end fed antennas without feedline to take the fields away from the operator?

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