AR Cover - EMR exposure

[VK5PO]

I am still bemused at the AR front cover depiction a month or so ago with a portable setup, clearly showing an operator sitting VERY CLOSE to a vertical
antenna. This must make the ACMA laugh, when the WIA's AR magazine has on its front cover, the clear proof that amateurs do not take EMR issues seriously.

No wonder the 1kW trial bit the dust.

It really is a poor reflection (no pun intended)

We do NEED to take the EMR aspect of the hobby seriously.

YES, I AM a PROUD member of the WIA, the worlds OLDEST AR organisation!

73, John

[VK3BQ]

The exposure limits on a 2.5w Sota station running an end fed wire at 7Mhz are cm's (I guess it was a Sota pic?). I'd be more worried about that 5watt 438mhz hand held at your head

[VK5PO]

Oh, a 2.5w SOTA station on 40m???
You must have been there Andrew..?.....

Or is it pure speculation like many other occasions?
John

[VK4BG]

About the only thing I'd be worried about sitting that close to that QRP Station antenna , was a dose of sunburn from being out in the great outdoors...did he have a hat on ? This EMR stuff in relation to AR is really over the top.

73
Glenn
VK4BG

[VK5PO]

Yes Glenn, It may well be over the top, but the requirements are there to be adhered to.

That is how things seem to be moving these days....


Hope the IC7700 is still going well?

73, John

[VK3BQ]

Oh, a 2.5w SOTA station on 40m???
You must have been there Andrew..?.....

Or is it pure speculation like many other occasions?
John

who knows how much power it is, lets make that 5w and see what the maths tell us, still cm's of exclusion zone? how about 10watts, still cm's.? nope, still not dangerous, a majority of sota stations have a ft817 (5w at 12v. usually 2.5w) some have a kx3 (5-10watts) and some have a ft857 (which can run more power, with a big 12v battery, 25w.. that needs a bit of an exclusion zone , still CM's..),

i don't know what its running, no, so it is just that, speculation, like your assumption that it was dangerous.

maybe he carried his icom 7800 and 2kw amp and 4kva petrol generator in the snow and really wanted to make some noise, then good luck to him!. i didnt see any dogs or a sled in the photo though,. so its also speculation.

[VK2JDH]

I am still bemused at the front cover depiction a month or so ago with a portable setup, clearly showing an operator sitting VERY CLOSE to a vertical
antenna. This must make the ACMA laugh, when the WIA's AR magazine has on its front cover, the clear proof that amateurs do not take EMR issues seriously.

73, John

You are making wild assumptions

[VK5PO]

Vk2JDH.... are you kidding?

Assumptions? No assumptions at all.... Sitting next to an antenna that close regardless of TX frequency, shows
rather basically that EMR guidlines are just not followed...

We HAVE to be mindful of our obligations, if not to ourselves, surely others in the proximity.
I did not make the rules, but realise that we as hams have obligations.

Where in tarnation is a wild assumption in that?

PS, how hard is it to write your name?

John

[ADMIN]

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[VK2DDS]

Assumptions? No assumptions at all.... Sitting next to an antenna that close regardless of TX frequency, shows
rather basically that EMR guidlines are just not followed...

Lets do some calculations/estimates then:

From the photo I estimate him to be ~1m from the antenna. This is the biggest source of error as the antenna is so large compared to the distance to the wire that a near field calculation should be done, but since that's rather complicated lets just do the typical physicist's approximation of a "spherical cow in a vacuum" and model the antenna as an isotropic point radiator centered somewhere near the middle of the wire.

Looking at the antenna (and knowing the culture of SOTA) I'll guess that he's operating on 40m, the ARPANSA guideline shows the general public exposure limit at 1-10MHz to be 86.8/rt(f) V/m (RMS), so 32.8 V/m at 7MHz (NB: the occupational limit at this frequency is 87.7 V/m).

Plugging numbers into a field strength calculator gives a maximum power under the above conditions to be about 22W. Since the ARPANSA guideline is an RMS time averaged limit (table 7, p12) this allows the photographed user to be running about 70W unprocessed SSB to remain within the general public exposure limit.

The major flaw with the above calculation that 1m from an antenna ~10m long the isotropic radiation approximation is probably rather wrong, near field strength of E and B would vary down the wire (I'm guessing E would be strongest at the end and B strongest at the feedpoint) so it may be that the above calculation meet the E field limit but not the B field limit at 70W SSB.

I don't know enough classical electrodynamics to calculate the near field intensity pattern, although I've got enough undergraduate study under my belt that given a few hours I could probably work it out if someone REALLY wants to know.

One thing I can do easily is assume a constant DC current in the wire and use the Biot-Savart Law to calculate a magnetic field intensity some radius from the wire. This might result in a reasonable approximation of the near field strength, but technically the Biot-Savart Law doesn't apply to changing currents, only static ones.

Cheers,
Brenton
(Off topic: As someone who grew up with Internet forums signing a post with you real name is just WEIRD. But, when is Rome...etc)

[VK2VHF]

It strikes me that many magazine cover pictures are "staged" to arouse reader interest and desire. Perhaps the fellow was just posing for the photo without transmitting

[VK5PL]

What he is sitting next to is probably not the antenna but the supporting squid pole.
The antenna is likely 7m above his head.
David
VK5NQP

[VK5PO]

Regardless of all the "guess work" and speculation, It just does not send the right message...


The bottom line is that you should not be that close to an antenna when TX'ing...

Forget all the "posing" , "antenna up the top" scenarios.
BE REALISTIC.

That is (hopefully) my last comment on this subject.

I bet someone else comes up with more stupid suggestions/scenarios...

The national AR magazine really should not depict an operator sitting so DARN CLOSE to an antenna.
John

[VK3AUU]

Why not ask the bloke in the photo what the real setup was before there is any speculation?

David

[VK5PO]

You really do miss the point David.
the POINT IS: as above:

PS, you should also find out the facts before posting wrong info too!

John

[VK2JDH]

Vk2JDH.... are you kidding?


Where in tarnation is a wild assumption in that?



John

No i'm not. Your wild assumption is based on you have no idea what power the OP was running.
I'm going to make a equally wild assumption and say he had a FT817 running HF SSB and was at least 1 M from the radiating element. (maybe I read the article) So well within the EMR safety guidlines.

A 3 G mobile phone operating between 1-2 Ghz running a few watts held next to a persons head has a far higher EMR and is still within the EMR guidlines.

PS, how hard is it to write you name?

John

You seem to be having a bad day.

Dave

[VK2AAH]

If we are going to get serious about EMR (and I agree with you John) please look at the October 2013 cover of AR and I would suggest to you that this is a far more serious breach of good engineering & practice than a poor guy sitting running QRP under a squid pole. Look at the 4 stack dipole array at, maybe, 4m above ground level and about 2-2.5m above head level- and that is a high power, permanent installation accessible to the general public not a portable, short duration situation. We have hams belly aching about having their repeater licenses wound back to 50W and they wonder why...

As I've told others when it comes to engineering & good practice "people in glass houses should not throw stones". Until such time as ALL amateurs accept that the same rules apply to them as to the rest of society we are not going to see any change in attitudes. The defense will always be "but VK0XYZ does it..."...

Cheers

Richard
VK2AAH

[VK5ZD]

I just asked the person in question: TX power was 2.5W

Sent from my C5303 using Tapatalk

[VK5PO]

WOW! someone sees past all of the What ifs etc, and actually sees my point, whilst actually seeing other issues.

It is NOT about being picky, It is about: "WE JUST GOTTA START TAKING THIS EMR STUFF SERIOUSLY"

Most of the comments above really reflect the widely held view that is is just not important.

I would hasten to guess that one or two stations will get "pulled off the air" because of EMR breaches.

Watch the excretory matter hit the fast rotating cooling device then....

John

[VK2AAH]

John,

I hear comments from mostly older amateurs that "the core of amateur radio is experimentation" and that normal rules should not apply to them.

I don't argue about experimentation but safety is not to be compromised in doing it. Amateurs should be setting an example of how things are done- after all they are doing it for the love of it- yet some just hide behind it to escape public scrutiny. That ain't going to happen no more... We know it is hard to meet modern standards on limited budgets but RF safety is just as important as 50Hz medium voltage safety... yet we have perfectly good power cables being tagged every 6 or 12 months. We have carriers spending a fortune to comply with EMR documentation yet some hams don't think it should apply to them just because it is a hobby? And some hams are complaining about repeaters being limited to 50Watts... Hello? Wake up!

Cheers

Richard
VK2AAH