EMR safety complience for vertical antennas

[VK4WDM]

I have been told by a local ham who is knows a lot about such things, that the "rule of thumb for" ACMA inspectors when assessing antennas for EMR safety is that "no part of the antenna should be touchable."

That means, for wire antennas, a minimum height of 4m for any part of the antenna, that being twice the height of an average person. This appears to be a very sensible and practical rule of thumb.

In the case of ground-mounted verticals, a barrier must be erected around the antenna to prevent it being touched. Obviously the distance of the barrier from the antenna needs to be greater than the calculated EMR exclusion zone. Some wire mesh will do it, but a bit unsightly and maybe not XYL friendly.

Another way to deal with a vertical would be to mount it on a pole so that the base is 4m high. I am going to do this with my vertical to try and improve its efficiency anyway, but I will have to use elevated radials and the ends of those will not be 4m high. They will droop down to the level of my 2m high wooden fence and the 80m ones will run along the top of the fence.  So they could be "touchable" - with some effort, but they are counter poises not radiators.

So is this still compliant?

Please be sensible and don't turn this into an ACMA bashing exercise.

73

Wayne VK4WDM

[VK4ADC]

Wayne

Download the VK3UM EMR calculator from http://www.vk3um.com/emr%20calculator.html

It gives you physical isolation distances for various bands and your transmitter power.

Don't use a metal mesh (eg chainwire fence) around the bottom else you will get currents induced in the sections and the possibility of introducing transmitted intermodulation products plus affecting the polar pattern.   A poly rope/s on stakes (eg star pickets or PVC pipe) spaced out from the vertical is probably enough of a barrier to stop anyone getting close enough to actually touch it, or at least warn them that they shouldn't.  That physical separation means that you don't need to raise the antenna base to the 4M level and still be compliant.

If you don't want to have to leave the star pickets/PVC pipes in place when you are inactive, sink a set of suitable diameter pipes into the ground so they are at ground level, or just below, and then place the star pickets & barrier rope into the pipes when you need to.  This arrangement would make it easier to mow the grass too....

I think the EMR rules are in place for those times when you are actually transmitting, rather than all the time, so a removable barrier option should still provide compliance.  In the event that an ACMA compliance check is undertaken, simply put the barrier poles & rope/s back in place to show that EMR compliance is understood and being observed.

Common sense must prevail.

Doug

[VK3RX]

There was some discussion on VK Logger about compliance.
One speculation made was that if an antenna was confined to an area that did not have public access e.g. back yard with locked gates, and antenna clear of boundary fences by the required distance (e.g. AM Broadcasting stations), compliance could be argued to be met. People who did have access to the yard i.e. family members would be educated what not to touch and what to keep clear of.

A view not tested as far as I am aware, and probably not the sort of thing to ask the ACMA about, otherwise their legal people may make an unexpected and/or unwanted determination.

[VK2CSW]

I work in an industry where RADHAZ (radiation hazards) is an ever present safety theme.

At work we are dealing with kilowatts and ranging in frequencies from HF to microwave, so we use a number of layers of protection, but in this case I will only refer to those layers that apply only to personnel not working on or with the radiating equipment.

First up, we use a visual notification as you enter the work area that indicates either RADHAZ (in Red) or RADHAZ SAFE (in green). Red means the systems may radiate, green means all radiating systems are locked out. (Warning and Education).

Certain areas (especially near antennas, wave guides etc) are designated as RADHAZ zones, regardless of the RADHAZ status, anyone entering those area must seek permission and be signed in and out of a log. Clearly permission will be denied if the RADHAZ is present. (Active Management).

Many areas are locked if RADHAZ is present (Physical Barrier).

Relating this back to a Ham Shack and Antennas:

Physical Barrier - Preventing ingress to the area while RADHAZ is present is a given - fences, gates and physical separation are the obvious methods.

Active Management - being aware of who is about when using the equipment is the key. Is a log book overkill? I would think it was, but the operators should be aware of who is about and exercise care, reminding those about not to touch is not unreasonable.

Warning and Education - This is a sticky one. Signage may invite neighbour issues. If the emitters are in use when visitors are present verbal warnings would suffice I would expect.

If the three management elements are satisfied, then I would think that the ACMA Field Officer would be hard pressed to find major fault.

The field officers I have met have been professional and want to work with, rather than against, the people they deal with, so if sensible steps have been taken then I wouldn't expect any issues.

[VK4WDM]

Sorry Guys, I hid my real question behind some other stuff.

I agree about what has been said about ground mounted verticals. Doug, I should not have metal mesh. We have plastic mesh at VK4KG and it works well. All EMR measurements have been done and exclusion zones calculated but this "no touch rule" appears to extend beyond just the exclusion zones.

My intention is to to pole mount the vertical and use elevated radials as per the manufacturer's suggestion to improve efficiency on the higher bands, not to comply with EMR.

The important question is: Given the ACMA inspectors rule that no wire antenna can be at a touchable height , will my elevated wire radials have to comply with that rule?

I have not received a visit from the RI's, but those who have found them to be very supportive of AR (one of them was a ham) and trying to make EMR compliance as simple and practical as possible.

Wayne VK4WDM

[VK5TM]

The important question is: Given the ACMA inspectors rule that no wire antenna can be at a touchable height , will my elevated wire radials have to comply with that rule?

My interpretation of that would be: - The radials are part of the antenna, ergo, they need to comply with the rule.

And "wire" in the antenna description is a bit misleading, as the ruling applies to antennas made of any material (including "wet string" ) and to "any part of the antenna".

[VK4WDM]

Hi Terry

to "any part of the antenna".

This is where things get very murky.

I can see the sense in having a barrier to stop somebody grabbing a RF hot radiating element and to keep people out of the EMR danger zone, but in the case of a ground mounted vertical they will still be walking close to, and over, the radials that extend well beyond the said barrier. Often they are just laid on top of the lawn and pegged down (as mine are), draped over garden beds, along fences etc and are certainly "touchable", at least in some places.

What about a vertical mounted on the top of a steel shed which then becomes the ground plane, and by your interpretation, part of the antenna. Difficult to make the shed untouchable!

Wayne VK4WDM

[VK5PJ]

Hi Wayne
you also need to consider power levels in your planning. the vk3um EMR calc software is very handy for visualising the situation. I used this as a planning aid for a VHF high power permit application some years ago and learnt quite a bit from it during the process. I say this about power because an antenna is only a threat once it is enegised and the level of threat is dependant on the power level being used. I know most of the 1KW HP trial permit holders failed on EMR because parts of antennas were to 'exposed' to human contact. What that actually was I am unsure but using the VK3UM software you can see what exclusion zone it gives you for an antenna / power level combination and not rely on us bush laywers in forums :-)
Peter, vk5pj

[VK4WDM]

Hi Wayne
you also need to consider power levels in your planning. the vk3um EMR calc software is very handy for visualising the situation.  I used this as a planning aid for a VHF high power permit application some years ago and learnt quite a bit from it during the process.   I say this about power because an antenna is only a threat once it is enegised and the level of threat is dependant on the power level being used.  I know most of the 1KW HP trial permit holders failed on EMR because parts of antennas were to 'exposed' to human contact.  What that actually was I am unsure but using the VK3UM software you can see what exclusion zone it gives you for an antenna / power level combination and not rely on us bush laywers in forums :-)
Peter, vk5pj

Hi PJ

Yep, done that for every band between 1.8m and 23cm and for every antenna I use. I never run more than 100w on HF and much less or VHF/UHF so all except 23 cm came up with  "ACMA level 2 compliance not required" but me being me, I did the calculations anyway. The exclusion zone on the vertical came out at about 3m (my gated back yard is more than 3mSq) and the inverted Vee which is 8m high in the centre was less than 1m.

It's this "antenna must not be touchable" ruling by the RI's" that has got me a bit confused.

Wayne VK4WDM

[VK2CSW]

I do wonder if this 'rule of thumb' is a thing or if it is yet another example of 'Chinese whispers' (are we allowed to say that any more?) which the bush lawyers have got a hold of and in true bush lawyer style, missed the point, missed the meaning and above all missed the truth of the matter.

If this is, in fact, a real 'ruling' then the ACMA must have published it somewhere - the field officers need to base their enforcement and guidance in fact, not gut feel.

I mean "not touchable" is pretty meaningless. How did you put it up without touching it? How could someone touch it, if it is in a private yard that is enclosed? What if they came into your backyard, without your knowledge, with a ladder, then climbed the ladder and touched the wire? As I said it is too vague and too meaningless.

[VK4WDM]

Hi Colin

This info is fairly reliable. It came from a professional RF person and ham who spent time with the RI's last time they were in this area. The conversation as told to me was: "the ends of the antenna (in this case an inverted V was being discussed) need to be more than twice the height (more likely the reach) of a person, about 4m, so they cannot be touched."

To me that means "no matter what calculations you might have done to determine exclusion zones (or don't need to do if ACMA level 2 compliance is not required) the antenna  must not be touchable. I think that is reasonable and sensible, but how does it translate to a vertical and its radials?

Wayne VK4WDM

[VK2CSW]

A question then, the answer for which I should know but I don't.

My meagre experience with ground plane antennas makes me think that there is very little energy in the ground plane. This comes from experience with mobile installations and a few 11m marine installations I have worked on.

If this is the case, what is the risk if someone touches the ground plane (radials in this case)?

If the risk can be shown to be negligible then I would think that the "rule" wouldn't apply.

BTW I occasionally run into a former field officer who lives somewhere locally, I'll run it past him next time I see him at the shops.

[VK4WDM]

A question then, the answer for which I should know but I don't.

My meagre experience with ground plane antennas makes me think that there is very little energy in the ground plane.  This comes from experience with mobile installations and a few 11m marine installations I have worked on.

If this is the case, what is the risk if someone touches the ground plane (radials in this case)?

If the risk can be shown to be negligible then I would think that the "rule" wouldn't apply.

BTW I occasionally run into a former field officer who lives somewhere locally, I'll run it past him next time I see him at the shops.

Another source of the "not touchable" viewpoint. Ron Cook VK3AFW in his Article "Some thoughts on implementing a 15W EIRP limimit for 60m" in the latest AR Mag (very informative read) writes when discussing antennas: " Any antenna wire that is within reach is not compliant with the electromagnetic (EME) emissions ARPANZA standard.

Colin, I agree, there should be very little energy in the ground plane, if there is something is wrong. I think that "not touchable or reachable" means a radiating element not ground planes, radials or counter poises. It will be interesting to hear what your ex FO says.

We have a radiation safety officer at the RAAF Base. I will ask him his opinion.

I will put a plastic mesh barrier around the vertical just in case the meter reader has a mad urge to go and grab it when I am transmitting

Wayne VK4WDM

[VK3RX]

I think that "not touchable or reachable" means a radiating element not ground planes, radials or counter poises.

Hmm .... what about open line feeder?

[VK5TM]

I no longer have access the ARPANZA document that had all the details re the "any part of the antenna" comment which is a bit of a pain.

There was (I think) details re feedlines as well in said document.

New one due out this year, so it would be interesting to see what changes are made.

[VK2CSW]

I finally ran into the former Field Officer this morning. We had a rather wide ranging chat and I did remember to ask about "untouchable" antennas and "4m clearance".

To put it simply, he knows of no such rulings. With the caveat that the description normally used is that the antennas must be inaccessible. To this point, I further asked if does having the antenna in your backyard, that has fences and gates, make it inaccessible. The reply was that without seeing the actual situation he couldn't be specific, but in general terms that would probably suffice.

The 4 metre thing, isn't a thing.

He did mention that they also take into account access by family, friends and other residents of the property - steps must be taken to protect them. Educating them is a valid protection.

I asked specifically about a ground mounted vertical, his suggestion was tomato stakes and electric fence tape. It really doesn't need to be a sturdy fence (assuming it is the secured backyard) it just has to be a barrier.

I hope this helps.

[VK4WDM]

I finally ran into the former Field Officer this morning.  We had a rather wide ranging chat and I did remember to ask about "untouchable" antennas and "4m clearance".

To put it simply, he knows of no such rulings.  With the caveat that the description normally used is that the antennas must be inaccessible.  To this point, I further asked if does having the antenna in your backyard, that has fences and gates, make it inaccessible.  The reply was that without seeing the actual situation he couldn't be specific, but in general terms that would probably suffice.

The 4 metre thing, isn't a thing.

He did mention that they also take into account access by family, friends and other residents of the property - steps must be taken to protect them.  Educating them is a valid protection.

I asked specifically about a ground mounted vertical, his suggestion was tomato stakes and electric fence tape.  It really doesn't need to be a sturdy fence (assuming it is the secured backyard) it just has to be a barrier.

I hope this helps.

That sound's like good sensible and practical advice Colin!  Might as well grow some tomatoes on the stakes. Will the RF make them bigger or smaller?  

73

Wayne

[VK3RX]

[quote pid='2508' dateline='1533716533']
Will the RF make them bigger or smaller?  

73

Wayne

[/quote]
Probably cause a mutation

And many thanks for the info, Colin.

I have a folder here containing my licence, copy of the LCD, ACMA EMR standard and printouts of the VK3UM reports on my various antennas, so I will add to the compliance declaration something in writing re what measures have been taken.

[VK5TM]

Thanks for the the update.

Now all I have to do is make all our 4 foot backyard fences 6 foot ones   (back fence needs some "maintenance" anyway).