Hi Tom,
A few comments interspersed below....
> > With respect to the "radial field", how essential is it
> > to have the radials evenly spaced in a full circle?
>
> Say you have one radial. The largest improvement occurs when
> you add one more radial 180 degrees from it. Add two more,
> and the largest improvement is when they fill in the hole.
>
> When any two wires eventually get where the open end spacing
> or largest gap is .025 to .05 wl, they pretty much appear
> electrically as a single solid sheet.
That's a great explanation!
With a little math.... on 160 (1.825 mhz), using 234/f for 1/4 wave -
the radial length should be is 128.2'.
If I remember correctly, the circumference of a circle is
2*Pi*r so that would be 2*3.142*128.2' = 805.6'
.05 wl spacing on 160 (1.825 mhz) would be 984/1.825 = 539.2'
So, .05 wl spacing would be .05 x 539.2 = 27' between the
radial tips in the circle.
To determine how many radials there would be in a circle
we would divide 805.6 / 27' = rounded to 30 radials
So for .05 wl spacing we would use 30 radials, and for .025
spacing we would use 60 radials, which is the "magic number" that
has been commonly cited many times before.
> If you keep all of that in mind, you will know the answer to
> your question. If you have wires within .025 to .05wl
> maximum spacing, it does no good to add more. If you want to
> add some, narrowing the widest gap will generally improve
> things the most.
> > Or asked another way, if you can get 40-50 1/4 wave
> > radials down, but you have to eliminate 40 or 50% of
> > the "circle", how dramatically would that affect
> performance?
>
> Depends on the antenna you are using. With a short vertical
> having low internal loss, it would seriously hurt
> efficiency. As a matter of fact if you had 40-50 quarter
> wave radials in 180 degrees, you would be wasting wire. You
> could reduce that number to 20-30 and have almost no change.
This makes sense. But now lets say that we are talking about
this "gap" in the radial coverage of say 120 degrees, for either
an Inverted L or one leg of a 160 4-square, how much is the pattern
degraded?
Is the pattern degradation in the direction of the "gap" in radial coverage,
or is the pattern degraded equally in ALL directions?
Are F/B, F/S and forward gain lost, or are F/B and F/S lost?
73
Bob KQ2M
www.factcheck.org Get the FACTS not the rhetoric!
> It's not how big you make it, it's how you make it big. Use
> as many as long as you can but spread em out as much as
> possible.
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|