GP14 Sailing Forums Forum VHF Licence Changes

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    • #21437
      Oliver Shaw

      Yesterday I received an almost incomprehensible email from Ofcom advising that the terms of my VHF licences are to be changed,  to ensure compliance with “the internationally agreed levels in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) Guidelines for the protection of the general public from electromagnetic fields (EMF)”.   They then refer to these levels as the ICNIRP general public limits.

      No doubt other members who use VHF  –  predominantly cruising members  –  have also received or will shortly be receiving similar emails.


      See their web page at   I offer that information because,  although it is to be found in the small print of their email,  it is not presented as a link,  and it is very far from conspicuous;   I had to read the email twice to find any means of sourcing further information!


      Even though I am a retired physics teacher,  with a degree in electronic engineering,  I found myself struggling to make sense of what they were telling me.   Agreed,  they make it clear that they are about to vary the terms of licences,  in order to comply with the new standards.   Agreed,  if we are using proprietory equipment of reputable manufacture we would hope and expect that it will already comply.  


      But how do we make certain that we comply?    And what limits do we have to observe as operators?   That is very far from clear.


      The good news    I think    is that they do provide a calculator for what seems to be a relevant quantity,  in the form of a spreadsheet;   the actual calculator is on the second worksheet of the spreadsheet.


      One starts by entering two pieces of data in the two labelled and highlighted (yellow) cells.  


      • ·         First,  (maximum) transmitter power (in W) in cell (D5),  which should be easy enough;   normally 5 for an older hand-held set (but 6 for some of the latest ones,  and only 3 for some entry-level ones).    Normally 25 for a fixed set,  but you are unlikely to be using that in a GP14;   but this will be relevant to those of you who also sail yachts.
      • ·         Also enter the transmitter frequency (in MHz) in the cell immediately below (D6);   the VHF channels are spread a short distance either side of 160 MHz,  but entering 160 is good enough.  (Indeed my reading of the technical annex is that all values in the range 10-400 MHz fall within index category 1,  and therefore give the same result.)

      Ignore the next two labelled and highlighted cells (pastel blue),  which are annotated as being for information only;  they have values already entered,  and they are protected cells,  so they won’t allow you to change the values already there.


      After entering each piece of data press either ENTER,  or any cursor arrow,  and the result of the calculation is shown in the labelled and highlighted (mauve) cell D14 (not D16 as stated!).


      That result is a distance,  which works out at 1.60 m for 25W transmitting power,  or 0.71 m for 5W transmitting power.    My reading of the fixed information is that this distance needs to be added to the (fixed) 0.30 m of the “Reactive near-field zone”,     so:


      25W   →   1.90 m total,  and

        5W   →   1.01 m total   


      My reading of the information is that this is the minimum separation required between your transmitter antenna and any member of the public.


      However this calculated distance is stated (in the Instructions for Use panel) to be a conservative result,  which will normally overestimate the compliance distance,  and smaller separation distances do not necessarily indicate non-compliance.   They also say that although it is normally appropriate to enter the maximum transmitter power it may be appropriate to use the average transmitter power,  adjusted for the duty cycle (e.g. over the six-minute averaging period specified    ).  


      So,  in my case,  I am not worried about compliance:   for my fixed set (on the yacht) my antenna is at the top of my mast,  and the radiation is horizontal.   It is (almost) inconceivable that any member of the public would ever by within 1.90 m horizontally of the top of my mast when I am transmitting!   The one exception might be if I am lying against a quay wall,  dried out,  or floating but with the tide very low,  and there happens to be a member of Joe Public standing on the quayside adjacent to the boat.    But technically one should not be transmitting in harbour anyway …   


      But non-sailing boaters with their antennae at deck level may need to consider the implications of this calculation.   Such boats may include your club’s safety RIBs,  etc.


      For my hand-held set it is also fairly unlikely that there would be any member of the public within 1 m of me while I am transmitting;   but it is nonetheless worth being aware of the limitation.   And,  of course,  we ourselves are normally well within 1 m of the antenna while using a hand-held set     


      They do state that merely calculating the compliance distance is not in itself sufficient;   users then need to ensure that no member of the general public is within that distance while transmitting.


      Having said that,  I am not 100% certain that I have understood everything correctly,  but if you want further guidance Ofcom refer you to their website (if you can make sense of it!)


      And on the more general matter of radiation around transmitting antennae,   it is normal for some more powerful military or marine or industrial transmitters to have painted circles on the deck or the ground around the antennae,  as a reminder of the safe distance.  There are also many stories of technical personnel wandering around transmitter arrays at night carrying fluorescent tubes,  not connected to anything,  and they light up spontaneously merely from the radiated energy which they absorb       



      • This topic was modified 1 month, 1 week ago by Oliver Shaw.
      • This topic was modified 1 month, 1 week ago by Oliver Shaw.
      • This topic was modified 1 month, 1 week ago by Oliver Shaw.
    • #21458
      Oliver Shaw



      • For the purposes of enforcement, OFCOM has included family and friends to be members of the public.   The owner, skipper, radio operator and any paid crew of a vessel are covered by alternate legislation and are excluded from these provisions.   So, if you are carrying family and friends on-board you will need to comply.   (This is most likely to affect powerboaters.   But if your yacht antenna is at the top of the mast none of your family and friends aboard are going to be within range.    OLS.)
      • Fit equipment in accordance with the manufacturer’s instructions and keep a copy of it on-board.  …     …    EMF calculator tool.   …   the calculator will provide you with a safe separation distance between the base of the antenna and members of the public. You should keep a copy of this calculation onboard.
      • Emergency communications are exempt from the regulations. Communications relating to the safety of lives at sea, when there is grave and imminent danger to a vessel or person and assistance is required are not affected by these regulations. However, whilst you do not need to comply during an emergency situation, the equipment does have to comply during routine transmissions, including radio checks.
      • The regulations only apply to equipment that can transmit in excess of 6.1W Effective Radiated Power (ERF). ERF is the total power radiated by an antenna, in the case of a typical 25W marine VHF radio set up, the ERF at the antenna is likely to be less than the 25W transmitter power due to the line loss caused by the length of the coaxial cable between the radio and antenna. VHF handheld radios transmit at a maximum of 5W and therefore are exempt from these regulations.  (Some of the latest ones are stated to transmit at 6W,  and that is quoted to only 1 significant figure;   so we don’t know what the first decimal figure is,  and therefore it is not immediately clear whether this is or is not less than the 6.1 W limit (which is quoted to 2 significant figures.)



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