Dave,
Do a neat trick with your antenna analyzer if it shows impedance:
Before you put ANY radials down, measure the Z at the antenna (at it's resonant
freq).
Then put your 8 radials down, and remeasure (make sure to correct for the
resonant freq shifting)
You should see the Z drop when going from 0 rads to 8 rads. I would be VERY
interested in your before and after measurements. (Be sure to do them at the
feedpoint, not in the shack). Please do the same thing if you use the values I
noted below for 25 radials or 16 radials (measure before (at 0) and after...and
report back the Z .
Also, if you have 500' of total wire:
25 radials 20' long will produce the best efficiency (more work, I know, but
that's what the formula for radial optimization says). This is for 80m band and
for 500' of wire.
This arrangement will outperform 8 radials of 60' long
If you don't want to go 25 radials at 20', then use 16 radials at 31'
long...the difference between 8 and 16 is substantial....and the very best for
the amount of wire you have is 25 radials 20 feet long.
=============================================================================
The key factor (at 80m) is 3 or 4 feet maximum separation at the tips on the
perimeter, no matter how long the radials are.This will permit the maximum
efficiency your propery dictates.
==============================================================================
Have fun!
73,
...hasan, N0AN
----- Original Message -----
From: Dave Tipton
To: hasan schiers ; Dave Tipton ; Jim Lux ; Bill Coleman
Cc: towertalk@contesting.com
Sent: Friday, June 16, 2006 4:25 PM
Subject: Re: [TowerTalk] re Radials
Ok, I like this idea and it makes the most sense. I just picked up 500 feet
of #16 Wire (TImes 2. Its basically lamp cord). I'm going to put down the
whole 500 foot spool with the lengths cut to 60 feet. I'll just snake em
anywhere I can, and then pin em down with some Lawn staples, or the equivalent.
I have 45 feet by 50 feet to work with.. It won't be perfect, but it will
work. I also have the antenna analyzer at the ready for final tune up.
I do have a tuner, but a flaw I've found in Hustler antennas, is they need to
be kinda close in frequency to the "Wanted" frequency to work effectively.
This especially holds true for their mobile antennas. Anything over 2.5 to 1
SWR generally turns deaf.
Dave, W3DMT
hasan schiers <schiers@netins.net> wrote:
Dave,
If you are going to lay the radials on the ground and the vertical is
ground mounted, then I think you would be very happy with the moderate
performance of 16 radials, 1/4 wave or so on the lowest band. There is NO
RESONANCE effect for radials that are on the ground or shallowly buried. If you
elevate the radials they must be individually tuned for a 1/4w for each band.
The spec for 3 on each band, at 1/4 wave long implies the antenna is NOT
going to be ground mounted, but rather will be supported a significant distance
in the air, thus becoming a "ground plane" antenna. Your performance with 3
tuned elevated radials on each band should be "decent", although far from
ideal. The primary variable for elevated radials is how high! The higher you
get the antenna as a portion of a wavelength, the more efficient your elevated
tuned radials become. If you get up 20 to 25' on 40m, the performance can be
quite good. On 80m it won't be as good.
Let's not get overly lost in the Take Off Angle (TOA), commonly called
angle of radiation. The key is how much power is put into the lobe of radiation
centered at the TOA, not the TOA itself. The reason I say it this way is if you
have very high ground return losses (poor radial field), your TOA will still be
low...but there will be very little power going into that TOA because it has
been eaten up with ground losses.
For this reason, a lot of people opt for the elevated ground plane with
tuned radials. The mistake they make, however, it not getting the base of the
elevated vertical high enough to cause the tuned elevated radials to "mask" the
high losses of the earth beneath it.
Again, for what you are talking about (moderate operational success, as
opposed to ideal), 3 tuned radials per band with a height of 15' might work out
just fine especially on 40m and 20m. The nice thing is, you can always add more!
73,
...hasan, N0AN
----- Original Message -----
From: Dave Tipton
To: Jim Lux ; hasan schiers ; Bill Coleman ; Dave Tipton
Cc: towertalk@contesting.com
Sent: Friday, June 16, 2006 12:16 PM
Subject: Re: [TowerTalk] re Radials
Well.. I have an old 5BTV (Hustler) that I'm going to put up this
weekend... It is spec'd for 1/4 wave radials on each band, telling me that I
need to have 3 on each band...
MY question... If I were to lay down 8 radials on 80, 80 on 40 and 8 on 20
(The only 3 bands I'm really interested in), do you think this would give me
sufficient performance to rely on it for some medium distance work? I'm not
going for big DX here, but I'd take it if I heard it.. I now have an 800 watt
amp in the mix too, so I'm going for as near resonant as I can get.
Dave
Jim Lux wrote:
At 06:52 AM 6/16/2006, hasan schiers wrote:
>Actually, they can be MUCH shorter than .22 wl, as long as you have enough
>of them. Many more shorter is quite a bit better than many fewer longer.
>
>There are free programs by G4FGQ, RADIAL2 is the name I think, but just
>google G4FGQ and you will get to his site and free downloads. The radial
>program is a good one and answers all the questions being raised. It lets
>you manipulate number/length/freq and ground characteristics to show
>efficiency. VERY HANDY!
Except that Reg's program isn't necessarily a very good model of
radials. He's modeling the radial field as a bunch of lossy transmission
lines (which is sort of fine), but doesn't account for the transfer of
energy into the surrounding soil, some of which reradiates, as opposed to
being simply loss in an equivalent loss resistance. Reg has some
explanation of what he's doing in the notes in the program, but doesn't
publish his algorithms or source code, so it's tough to figure exactly what
he's doing (and I'm not patient enough to just run lots of cases and
reverse engineer it). It's also not clear how Reg is modeling wires close
to the surface, where a significant part of the field crosses the
ground/air boundary.
That said, it might be a handy way to tinker around and gain some
understanding of the effect of various radials.
If you really, really want to model radials, you're probably best off to
fork out the bucks for a copy of NEC4 and do it right. (NEC4 does model
buried wires, and has been rigorously validated, and all the gory details
are published) Otherwise, just use the "throw lots of wire out, don't worry
about the exact length, and more radials is better than fewer" approach.
Jim
>The data I got is completely consistent with the ARRL publications that
>describe how to get minimum loss for a given wire length available, as well
>as with G4FGQ's program. I do think Reg's program is a bit optimistic, but
>it points one in the right direction. I have full faith in the studies
>published in the ARRL Antenna Handbook on how to optimize a radial field,
as
>my actual measurements agree very strongly with the article.
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