-----Original Message-----
>From: Chris Adams <n4vi@comcast.net>
>Sent: Aug 27, 2008 10:11 AM
>To: TowerTalk@contesting.com
>Subject: Re: [TowerTalk] ground radial length vs antenna height?
>
>Dave,
>
>It seems to me that the takeoff angle is going to be primarily
>determined by the characteristics of the ground outside the radial
>field. For example, to get low takeoff angles, requires reflection of
>the signal, with the correct phase, a long distance from the radial
>field. Whether this reflection takes place, and how efficiently it
>happens is dependent on the ground characteristics at that distance.
Indeed.. flood your neighbor's yard with salt water...
>
>The efficiency of the vertical is directly affected by the number of
>radials.
and their length. There are points of diminishing returns, though. The rule
of thumbs:
1) radials as long as the antenna is high
2) enough radials that the ends are some small fraction of a wavelength apart.
If you wanted to get fancy, you could lay a branching tree network of some
sort, to keep the spacing between wires roughly constant.
It's a labor vs cost of materials vs incremental performance thing.
BTW, I recall that there's not a huge effect from wire size (for radials laying
on the ground or buried shallow), so you pick your wire size for mechanical
properties and cost. (no matter how small the wire is, it's a heck of a lot
better conductor than some amount of soil)
>
>> ...N6LF has also published some excellent work on radial systems. It's
>> on his website. Google to find it.
>
yes, although his optimizations didn't necessarily trade appropriate parameters
(i.e. if your question is "how do I best use X feet total of wire" that's
answered, but the real question is "how do I best use labor hours at $X/hr and
copper at $Y/pound"
(and bearing in mind that labor cost for hams is highly nonlinear.. the first
couple hours are free, but as the sun gets hotter, and your back starts hurting
more from stringing all that wire, the notional hourly rate starts to rise
rapidly)
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|