Looking for some collective wisdom from the community, particularly those of you who sift through technical & legislative matters in great detail…which is probably most of the people on this forum!!!
I’m having a bit of an antenna reshuffle at my home QTH & out of diligence wanted to ensure that my proposed setup complies with RF exposure limits so that I don’t get in trouble for microwaving my neighbours in their garden!
On the RSGB web app, it shows both 1998 limits & 2020 limits. Which are we supposed to go by?
According to the 2020 limits, my proposed setup is compliant but according to the 1998 limits I need an 8m exclusion zone at ground level either side of the EFHW. I can’t see my neighbours agreeing to be banished from their garden while I play radio!
There is a line on the RSGB site that says the 2020 limits superceded the 1998 limits. I therefore assume that I should go with the 2020 limits?
That raises the question of why it still shows the 1998 limits?
That’s was completely fine back in the 60’s even encouraged but under the ICNIRP 2020 regs it should now read: Trying to fry snags at the neighbours’ barbie since 1961
8 m is 40 MHz. It’s an ISM band here and baby monitors often use it. Before Bluetooth cordless phone sets also used it. I learned a lot about my neighbours.
Always check your licence for allowable frequencies, modes and power.
It Is frequently used for experimental WSPR transmissions. Legal here if the power level meets local regs.
As stated earlier, use the latest version. For comfort, here’s a direct lift from RF EMF GUIDELINES 2020 “introduction” and also the blurb on ICNIRP’s website, under publications.
“This publication replaces and superseeds the 100 kHz to 300 GHz part of the ICNIRP (1998) radiofrequency guidelines, as well as the 100 kHz to 10 MHz part of the ICNIRP (2010) low-frequency guidelines.”
Please note their freestyle spelling of supersedes😂
40m band. Looking at possibilities between 300 & 1000 watts for NVIS when the rules change.
Before we open up the “you don’t need 1kw, it’s ruining ham radio” debate, I agree that it’s excessive for chasing SOTA stations running QRP but there are times when that extra S-point can make a difference.
In reality I’m probability going to run nearer 300-500 watts. Im just considering worst case scenario in case I ever get asked to proove compliance (however unlikely that may be).
Hi if you need an 8 m exclusion zone then saying that would have been clearer. I didn’t read that as your requirement.
I am reticent to say any more as the question is too open and I don’t want to be responsible for any misunderstanding
In my home station case I have to consider if any of my antennas have a field that exceeds the standards max level at the maximum power I can run. This includes considering the possibility of someone standing on the top of my back fence and reaching towards my wire dipole. It also includes considering the fields in the new multistory building that appeared next door.
You might see that I have no exclusion zone. Anywhere people could possibly be has to be safe.
I have used the computer program developed by Doug, VK3UM (SK) which can be found on the web. It is very comprehensive.
However, nothing beats understanding the regulations and the basics of field generation.
For SOTA, some members of the public may try to reach out and grab my antenna. You can’t fix stupid, so I would have to implement the stop transmitting action.
How does the hazard injunction go again?
Eliminate the hazard
Control or prevent access to hazardous areas.
(Apply administrative and/or engineering controls)
Use PPE.
Happened to me on DL/MF-079 in October of last year, a popular destination for tourists where, during an early morning activation, one of these officious types, a self-appointed guardian of public order, approached my antenna setup with what looked like an attempt to remove it. Of course, I stopped transmitting immediately (I had been running 15W, SSB) and asked him nicely not to touch the setup, which was my private property, which would be removed shortly, and that it would be best to move away from it, perhaps a couple of meters. There followed an exchange where he loomed threateningly and did his best to argue that I had no right to obstruct or spoil the view, where my small HF-Pro vertical was attached to a steel railing off to one side of the spacious summit platform out of the way of everybody, and the radials arranged on the floor parallel to the railings but also out of peoples’ way. Eventually, he disappeared - in a huff, natch - and I could continue. It takes all sorts…
Is that an 8 m radius cylinder centred on the dipole wire? If you erect the wire at 11 m then your neighbours will be fine and you will be IOK if you keep your hands by your side. And you will certainly have plenty of NVI signal on 40 m.
I’ll check what my preferred calculator says and get back.
BTW, all VKs are supposed to have a printout of their calculations showing proof of RF safety. Not required in the UK?
My interpretation of Ofcom’s EMF requirements is that UK licensees must provide evidence (measured or calculated) on request, but not specifically as print-outs. I have 42 PDFs from the RSGB EMF model on my PC covering the 19 home QTH and the main 23 portable (antenna/band/mode) combinations.
I probably could have generated a lot more portable cases if I considered every antenna physical configuration (inv-V, inv-L, inv-7, sloper) that I ever use and occasionally vary depending on the topology at the summit.
The premise of the Ofcom docs seems to be that any inspection would take place at the home address (as on the license doc) and not at a portable location. Somehow, I can’t see the OfCom bloke panting up a SOTA summit with me to check the portable setups.
Actually, I don’t think it had anything to do with the radio or antenna setup - I think the guy had a bee in his bonnet that somebody - anybody - should dare to put some thing, some equipment, be it rucksack, kiddie’s pram, whatever, at some place in a public area so as to possibly obstruct his or anybody else’s (i.e. his) ability to go wherever they would like. I also had one guy a few years ago who purposefully walked straight into and over my very visible linked dipole setup (his actions caused it to collapse to the ground!), which had been set up on a small part of a football-pitch sized flat summit and well away from the path and benches and summit cross, because … well, how dare I place something where he was entitled to walk? So walk he would, and walk he did. Frightful and childish behaviour.
I have Ed to thank for pointing me in the direction of the free EMF analysis program from the German BNetzA authority, which I’ll be playing with in the next few days.
This is about either the fear of the unknown leading to irrational behaviour or conflicting rights in a public place. In his (twisted) mind he might believe that his right to roam trumps yours to put something there.
I wonder if he would think it acceptable to stand exactly where a family is picnicking in a public park, perhaps even to walk on the picnic blanket. Deliberately knocking into your private property and potentially damaging it might even an offence in most countries.
On one G/LD activation (deliberately a bit away and below the summit) I was shocked to see one of two blokes attempting to open a drybag I had tied to the base of my antenna pole. They probably hadn’t noticed me sitting at one end of my inverted V. This conversation followed:
Me: Hello! Please don’t do that.
Him: Why not?
Me: Because it doesn’t belong to you.
Him: I wasn’t doing any harm.
Me: It doesn’t matter, please leave it.
Him: There’s no need to be aggressive.
Me: I wasn’t. I asked you politely.
Him: Do you have permission to do this?
Me: I don’t need permission to do this.
Him: [more rudeness]
Now the numbers here are for the ACMA requirements and I cannot say the results are more than indicative for elsewhere.
I didn’t find an 8 m exclusion zone for CW power into a 7 MHz dipole at less than 1.35 kW.
The calculations are for a 7.2 MHz dipole at different hagl and different powers. I used the VK3UM V7.12 spreadsheet.
At 100 W key down for 6 minutes, provided I am outside the range of 2.17 m from the wire I am OK. So mast heights of 5 m would do nicely.
At 1,000 W key down for 6 minutes the on axis (broadside) exclusion distance is 6.86 m so a pair of 9 m masts would be OK.
8 m masts (the highest not requiring building permit approval here) are more than adequate for 1 kW 50% duty cycle CW.
If you consider ground reflection then the situation improves as your pattern means less field strength in your yard. Over flying birds need to fend for themselves.
And for SOTA, 10 W 50% duty cycle the on axis exclusion distance is 0.48 m.
So James, if you use an officially approved process or approved calculator and it gives an 8 m exclusion zone then it is more conservative by 35% compared to VK requirements. And there really isn’t any way around it other than to raise the antenna or reduce the duty cycle.
Good luck
73
Ron
VK3AFW
Owns an air fryer.
Prefers rare steak.
what band and power is that for?
