Minchsailor
Well-known member
Well, I'm a physicist (although EMF is not my speciality), and after reading all the bumf several times I'm nowt the wiser. Suspect as others have mentioned, it is arse covering.
Changes to VHF licence
- Thread starter Dan Tribe
- Start date
Black Sheep
Well-known member
Apologies, I should have fleshed out my answer a bit... "no it isn't" on its own is a little bit trolly and I usually try not to do that.
First you're making a huge assumption - that the antenna is at the top of a mast. Mine isn't, even though I use sails. Motorboats also have them at a much lower height. It's quite likely that members of the public could be within a couple of metres of a such an antenna.
Even in the case of a mast-top aerial, there are occasions (in a lock; against a wharf; etc) that members of the public could be within the zone.
Second, you're ignoring the other part of the requirement - to demonstrate that your installation is compliant. Which means the set of calculations that came to 2m. And a set of operating procedures that clearly instruct the operator not to operate under any of the circumstances above when there is a member of public within the zone. (you may be as sceptical as I whether anyone will ever check this paperwork, but my understanding is that it will be a requirement)
Thirdly, you have said that your advice is to the "VHF marine radio user" (by which I assume you mean yachties with a SRC, limited to 25W). And that's fair enough within the limits, but many of us have other equipment on board (AIS transmitter, Radar, Radar transponder) and for those it is far from that simple.
Big caveat - I haven't ploughed my way through all the Ofcom bumf, so I might have some wrong ends of sticks here. But this is why we need some clearer guidance (I'm looking at you RYA! and you CA! And the magazines!)
Bilgediver
Well-known member
The installed VHF radios we use normally transmit at 25 watts on high power so yes it will affect us in some way. The point of all this is to make all people on board aware that RF can harm under certain circumstances and we will possibly have to have warning signs on board to ensure people do not inadvertently expose them selves to RF beyond acceptable limits. There is a calculator where you can check the risks of your equipment. One risk could be some one working at the masthead while someone else has a long conversation on the VHF.
The notice from Ofcom suggests that our installations could be inspected for compliance so I presume this means to ensure warnings are in place. How many of us will be told off when this happens because we do not have our Call sign and MMSI displayed adjacent to the radio.
. Tis a long time since the days of Bob B. inspecting radio installations around Central Scotland especially at marinas . A VHF antenna and no visible Radio Licence would result in a letter from Ofcom's predecessor.Found it and now going to read it all on PC.
EMF calculator
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longjohnsilver
Well-known member
Wrong!
RivalRedwing
Well-known member
I assumed it was a phishing e-mail and dispatched it to the virtual wpb immediately
ProDave
Well-known member
Well I will start to worry about it WHEN I see reports of random checks by Ofcom demanding yotties demonstrate their compliance with this new regulation.
Until then I will just go sailing.
Until then I will just go sailing.
Black Sheep
Well-known member
That's probably a sensible response.
Nobody has to do anything now, anyway - we're still in the consultation stage.
longjohnsilver
Well-known member
Same here. It didn’t even occur to me it was wrt my vhf license.
chriss999
Well-known member
I think I might submit a response to the consultation process. Asking them to explain in plain English what the rules are (once issued) and how to comply with them.
Praxinoscope
Well-known member
Phew! It would appear I am not the only one to be totally mystified by the Ofcom email, I tried to make sense of it (honestly) but eventually gave up on the principle that sooner or later someone will publish a comprehensible version.
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Never Grumble
Well-known member
You make a very good point, the fixed VHF yottie radios will all be about the same. The problem will be understanding the rest of it. Its even making me wonder if a push-pit mounted AIS aerial is still an option. Having paid membership for a couple of years, I think I might email the RYA and see if they can decipher it for me.
Reminds me of my days in the navy and man aloft procedures with keys and tallies.
Bilgediver
Well-known member
There is a lot to get through and the link seems to have failed at Ofcom so will need to search the site. The main concern for us is around the main VHF set which operates at 25 watts on full power. The minimum distance between members of the public and the transmitting antenna calculates at 1.6 metres. We have to ensure that no one is closer than this distance when transmitting at full power. This is not a problem on most yachts so long as the antenna is not close to the cockpit or no one has climbed the mast however it may be a problem on RIB's and motor boats and might be a concern for yacht clubs where "members of the public" drive and work on club boats. It seems we as licensed operators have to look after ourselves on our boats as long as every one else (the public) are kept safe.
As a matter of interest the public should be kept 0.71 M from a walkie talkie at full power (5W) and 0.32 M at low power (1W). If we are concerned for our selves we need to grow longer arms.
| Input parameters | ||||
| Transmitter power (EIRP) | = | 25 | Watts | |
| Operating frequency | = | 150 | MHz | |
| Reference levels from ICNIRP 1998 Guidelines | ||||
| Reactive near-field zone | = | 0.32 | m | |
| Referencel level for power density | = | 2 | W/m^2 | |
| Calculated result | ||||
| Separation distance R | = | 1.60 | m | |
st599
Well-known member
Sorry but this is wrong. The EIRP transmitter power is not 25W.
You need to add in the antenna gain.
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st599
Well-known member
| Transmitter Output Power | 25 | W |
| 13.95 | dBW | |
| Antenna Gain | 3 | dBd |
| 5.15 | dBi | |
| EIRP | 13.95 + 5.15 | dBW |
| 19.1 | dBW | |
| 81.3 | W |
To do it properly you'd need to remove some cable loss and take account of the duty cycle (i.e. during a conversation, what percentage of time are you transmitting)
The 81.3 figure is what's needed by the Ofcom spreadsheet.
JumbleDuck
Well-known member
As far as I can see from their spreadsheet calculator, they are allowing for an antenna gain of 1.64 (ie 2.5 dB). That gives a 2m compliance distance for a masthead VHF transmitting continuously and 0.3m for a Class B AIS antenna transmitting for 26.6ms every 30s.
Daydream believer
Well-known member
st599
Well-known member
The 1.64 is the difference in gain between an ideal isotropic antenna (EIRP) and an ideal dipole antenna (ERP). Seems a bit OTT for Ofcom to be expecting people to do this.
syvictoria
Well-known member
Whilst an unlikely/rare situation, I suppose that potentially a masthead VHF aerial may be an issue if moored alongside a wall with a big tidal range...
Bilgediver
Well-known member
There could be gain or loss depending on antenna. The spread sheet I posted was theirs.
.
Bilgediver
Well-known member
They have this conversion figure in their calculation to arrive at the figure that is of interest to the public.
