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

To: Jim Lux <>
Subject: Re: [TowerTalk] Radials Questions - 270 or 360 degrees.
From: Bill Coleman <>
Date: Wed, 5 Jan 2005 22:56:02 -0500
List-post: <>

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:
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