Re: [TowerTalk] Radials Questions - 270 or 360 degrees.

[Bill Coleman <aa4lr@arrl.net>]

On Jan 5, 2005, at 7:55 PM, Jim Lux wrote:

> The error in the model is probably a lot bigger, as Red said. Upshot 
> is, don't trust the 1.1dB number.  You could have 1 dB more gain, or 1 
> dB less gain, or no change at all.

Point taken.

> Somehow, I doubt any of the readily available inexpensive modeling 
> codes would adequately model the effects of your house, which will 
> dominate any directive effects of your asymmetrical radial field.

Definitely, since the house consists of a complex variety of 
components, some opaque, others transparent to RF.

> There you go.. the real useful advice.. put down as many radials as 
> you have time/money/patience for. Don't worry about the length 
> (well... extending past, say, 1/2 wavelength might be a diminishing 
> returns)

I've got down 24 radials of 60 feet (a few are shorter), which is about 
all I have space for in my 270 degree circle.

> > Question 2: In looking at option B, is the vertical segment going to 
> > have an adverse effect on the pattern in the NW to NE direction? Is 
> > the vertical segment going to change the phase of the currents and 
> > ultimately destroy any gains by adding the radials?
>
> No way to predict. One would probably be safe in saying that there 
> would be "some change", but it might not be detectable.  That wire is 
> presumably next to something (earth, concrete, interior structural 
> members, etc.  All of that will have an effect, and one that is 
> basically impossible to predict (at least without spending a lot more 
> time and money).

Option B would have the radials rise 9 feet off the ground, then 
traverse the basement ceiling, which is alive with house wiring, gas 
pipes, and aluminized mylar air ducts.

Option A would have the radials cross the basement floor, which is 
concrete, and much further away from the conductive parts of the house.

I was really asking about the effect of the 9 foot vertical riser 
within three feet of the shunt fed tower. Other feedback I received 
indicated this probably isn't a good idea.

> > > 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.

Bottom line - sounds like people are telling me it ain't worth 
bothering with running radials across the basement floor. Thanks, 
that's good advice.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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