[TowerTalk] Radials Questions - 270 or 360 degrees.

[Jim Lux]

----- Original Message -----
From: "Bill Coleman" <aa4lr at arrl.net>
To: "Jim Lux" <jimlux at earthlink.net>
Cc: "TowerTalk" <towertalk at contesting.com>; "Red" <RedHaines at centurytel.net>
Sent: Wednesday, January 05, 2005 7:56 PM
Subject: Re: [TowerTalk] Radials Questions - 270 or 360 degrees.


>
> On Jan 5, 2005, >
> >>> Question 3: Is there any coupling or danger associated with having
> >>> these radials inside the house? Is there a potential for high
> >>> voltages to appear, or to have the elements radiating RF inside the
> >>> structure? Is this different from option A or B?
> >
> > Yes.. and this is probably the best reason to NOT do it. Putting
> > antenna components (of any kind, connected anywhere in the system,
> > ground radial, radiating element, whatever) in close proximity to
> > people and/or flammable stuff is not a good idea.  If nothing else,
> > since you couldn't do a credible model, and I assume you intend to use
> > it for transmitting more than a trivial amount of power (e.g. a few
> > milliwatts), you'd have real trouble complying with the FCC RF safety
> > regulations (47 CFR 97.13). How would you assure that you're not
> > exceeding the RF exposure limits?  (And, no, I don't think the
> > categorical power exemption for amateur stations would apply here.
> > Take a look at page 9 of OET Bulletin 65, Supplement B... it's on the
> > web)
>
> We're talking 80m and 100 watts. Page 9 of OET #65, supplement B is a
> diagram of the electromagnetic spectrum. Page 3 of the same bulletin
> indicates that for power levels under 500 watts on 80m, an RF Safety
> evaluation is not required.
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/
oet65b.pdf

Maybe it's page 9 of the downloaded pdf file (yep, it's labeled as page 4 at
the bottom).. In any case, there's a whole paragraph  (starting "Many
classes of...") that goes on about how the limits in table 1 (the 500W for
80m) only apply in "normal" situations. It specifically talks about
nonstandard installations like balconies, dwellings and mobile, and leaves
the FCC the option of asking you to verify.  You can't get away from 1.1307
(the usual RF safety clause)... OET bulletin 65 supplement B was basically
the results of a negotation between hams and the FCC to give hams a "safe
harbor" to avoid having to do the full on survey required of basically every
other RF emitting installation. (i.e. waving the Narda wand, etc.).

If you (or anyone else contemplating giving short shrift to the RF safety
aspect) ever run into a contentious situation with neighbors and such, you
don't want to give them any excuse to raise the "safety" flag, because if
they decide to push it, all the PRB-1 in the world won't help you avoid
having to go to a heap of trouble.  Even the commercial guys tend to tread
lightly here because the last thing you want is the evil word "radiation"
coming up in some sort of proceeding, even if sunlight is a electromagnetic
radiation power density of a kilowatt per square meter.

And yes, the FCC does check this stuff.  Take a look at the recent
enforcement bureau actions with respect to some transmitters on top of Mt.
Wilson. They may grind slow, but they get there..
http://www.fcc.gov/eb/News_Releases/DOC-255217A1.html  10 kilobuck fines,
but the measurements done in 2002.