Ofcom EMF risk assessment & UK SOTA (part 3)

The RSGB “EMF-2” EMF compliance guidance PDF (downloadable from the RSGB website) says one must do a compliance check (e.g. run the on-line calculator) for all “equipment configurations”, i.e. different combinations of frequency (band), [maximum] RF power, mode, antenna & location.

I created a spreadsheet and have 19 configurations for the home QTH and 23 for portable. It’s a good job I’m mainly CW and do other modes (e.g. SSB and FM) on just a few bands.

Here’s a sample to illustrate my point:-

So, before I start running the calculator for all 42 combinations, could someone confirm I’ve got it right?

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I’ve been ignoring this subject because I thought it didn’t apply for 10W and below - putting aside for the moment how the 10W is measured/assessed taking into account antenna gain.

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That’s my understanding Andy. I don’t think you need to worry about what the rig is; the key variables determining whether an assessment is required are: band, mode, power, antenna & location.

Hi Andy,

In VK the ACMA mandates maximum field strengths. Doug VK3UM (SK) produced a calculator that I and many others have used. I think the end result is likely very similar to yours. A simplified assessment procedure was issued by the ACMA.

Apart from assessing my home station, I have, for portable use, taken a few worst examples. Eg quarter wave vertical on a perfect radial system and 50% duty cycle max carrier. This gives a higher near field than an inverted vee at 7 m.

Prevention being better than protection, I stop transmitting if anyone is within 3 m of any radiator of low gain.

Having a comprehensive spread sheet calculation is extra work but if arrested for irradiating a member of the public it could be a useful defence. Carry it in a zip bag to keep it dry.

I have objections to some of our requirements that arise from an attempt to blanket cover the perceived problem with simple rules. However, and this is important, not complying to laws and regulations relating to safety will never turn out well.

Being scientifically and medically correct is small comfort if the magistrate finds you broke the law and applied a penality.

Good luck.



Andy, I’m not sure that you need to do this if you’re running a typical QRP SOTA HF station. One way I could get the calculator to go red at the bottom (with 10 watts radio output) was to select FM and enter 100% transmission time in 6 minutes. That’s pretty extreme though.

The typical example below - 10 w into an inverted V up a 7 m pole, comes well within limits.

Looking at a typical high power VHF portable set up, 50 w into a 4 element beam on 2 m SSB doesn’t trigger the calculator, however using the same set up on FM does.

My suggestion would be to run the calculator for powers over 10 w into a gain antenna for constant carrier modes, eg FM. For 10 w CW or SSB into a wire you should come well under in all cases.


That is correct but it is 10W EIRP. A dipole has 2.15dBi gain so if your rig has 10W output you could still be over the limit. However, there is a mode factor (e.g. 40% for CW) and a transmit % in 6 minutes factor (I use 50%) which reduces your power. So in practice there should be little issue with low power SOTA. Note that you don’t have to assess every combination if the EIRP is less than 10W.

The new RSGB EMF calculator has shown that my home station is almost compliant so I don’t think the new regulations are as bad as people have worried. I mostly run QRP but if I do fire up the FT450D I have found that all I have to do is reduce the power to about 75W. With some minor changes to the antenna wire I should be able to run 100W on all bands.


If i get these numbers for an antenna at home. Further assessment required means what? Does it mean I
just need to ensure people stay at least the compliance distance away from the antenna?

The height at 2m is the lowest point(one end of the antenna). Although i could alter that to make it higher if need be. its only a temporary antenna i put from the hosue to the tree anyway i usually do 90% of operating from hilltops anyway.


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Reduce your power output readings until you are compliant, or raise the antenna further out of harms way.

73 Phil


2 green boxes i take it means i’m compliant?

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Or make sure no one is within the distance specified at the bottom of the calculator.


Further assessment means you have to ensure no one is within the distance shown while you are transmitting. So if the antenna is at least 50cm inside your garden then you are fine, provided no one is in your garden (even your own family). Or if you can see that no one is too near the antenna then you can safely transmit.

That’s basically every summit I’ve activated in GM/ES


That’s not the case for me. For example, yesterday I set up my tarp behind a rock a little below the summit to get shelter from the wind and rain. My EFHW went back up towards the summit behind so I couldn’t see the end. But I run 5W so once you take into account the mode factor, 50% transmit/receive factor even if there is any gain I am well below the 10W. Obviously if I was to run higher power I would set things up so I could see the antenna.

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… or you may buy some of these signs.


Can anyone explain why I am not allowed to use RG174 on 80m? All is fine even at 30W (in case I use the 857 or an RF amp). I started at 20MHz and all was OK down to 60m (my usual start band) but when I tried 80m the feeder was deselected and RG174 was no longer available on the drop-down.

Also I don’t understand why for my home G5RV with 100W at 6m min the arrangement is flagged up as needing closer inspection when the clearance above head height is 4.2m.

The backed up files do not seem to restore.

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I suggest you report apparent bugs in the app to the appropriate person (look at the bottom of the calculator). I can see that the feeder types have change for 80m so it does look like a bug to me.

If you post screenshots of the calculator then it will be easier to understand any possible issues.

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There are a couple of bugs with the app (which I’ve reported) which make it take a bit longer to complete than it should. However, overall I thought the process was quite painless. I don’t think any of my set-ups required anyone to be further away than the RSGB’s recommended minimum distance of 2.4m. I think my most vulnerable condition is whilst operating mobile from the car (especially when stationary). One to watch for when pedestrians are passing.


Yes, I agree. The rigs that you see in the (above) sample from my table of equipment configuration spreadsheet are just an aide memoire to help me working out the combinations I actually use at home and when portable.

I disagree, fellas.

Reading the RSGB EMF compliance guidance [mentioned above] I don’t think you can simply say to Ofcom that you only ever use low power (e.g. 5W, 10W) and claim you must be compliant.

Quoting the relevant passage:

The 2.4m separation guideline obviously cannot apply to hand-held or body-worn radios. For these and many other low power situations, Ofcom allows compliance to be demonstrated a different way, by showing that the time-averaged EIRP is less than 10W (and also that the peak EIRP is less than 100W). If you can show that, then no further assessment is required – but you still have to calculate the EIRP and record that fact. This low power compliance route applies to almost all VHF/UHF 5 watt handheld radios

[I highlighted the important points in bold].

As others have said, you have to take account of factors like antenna gain. So, one has to demonstrate by calculation (e.g. using the RSGB calculator) or by physical measurements that your equipment meets the low-power criterion then document the results, and not just assume it does.

Just to be clear, I’m not worried about being compliant in most cases [I’ve already used the current and previous versions of the RSGB calculator]. It’s the sheer number of times I need to run it that will be bothersome (e.g. my max power, mode and antenna might be the same but I operate on all bands 80m - 10m, so I need a calculation for each band).

Of course, if anyone thinks I’ve misinterpreted the requirement and has a convincing explanation I’ll be happy to hear from them. Otherwise, I’ll be slaving over a hot online calculator for some hours this weekend.


I’ve found that the [latest] RSGB online calculator is very quick to do all nine bands 80m to 10m if the RF power, mode and antenna / height / feeder type & length don’t change. Having done one (say 80m) and saved the PDF with an appropriate filename, you then select the next band from the pull-down menu (e.g. 60m) and it re-calculates automatically.


Yes Andy. I fear it will take me some hours to complete my calculations. I have in effect 7 antennae, which includes a dual feed 2m cross yagi, which I am counting as two. I have 14 calculations to do over 12 amateur bands to complete my set of data, from 160m-2m. I’m not currently operating 4m so I can leave that band out.

73 Phil

PS “Life’s too short for QRP” that statement is bound to upset folk. It wasn’t me than penned it however, so don’t blame me!