Hi Ron,
We are not that far apart ... the key is as you mentioned,
"special design considerations" ... that's the important piece.
Otherwise we end up with 'ham lore' that seems to think
that 2 elevated radials equals 100 in the ground. Not so.
QSL on the modeling software, that's been another challenge
in the past as to accuracy, now we have better tools.
73 de Billy, AA4NU
----- Original Message -----
From: "Ron Castro" <ronc@sonic.net>
To: "Billy Cox" <aa4nu@ix.netcom.com>; "Discussion of Ten-Tec Equipment"
<tentec@contesting.com>
Sent: Saturday, August 16, 2008 1:30 PM
Subject: Re: [TenTec] OT: Ground Radials at Tower Base
With all due respect to W8JI and ON4UN, there has been a lot of more
recent research done by commercial AM broadcasters over the past couple of
years regarding elevated radial systems for vertical radiators, especially
in light of recent copper thefts of traditional buried 120 radial 1/4 wave
systems. The current leader in the application of these elevated systems
is Ron Nott of Nott Ltd. (I don't think he's a ham) and you can read a bit
of related materials at his website:
http://www.nottltd.com/AMGroundSystems.html
The bottom line is that elevated radial systems can work as well as
standard buried systems, but there are some special design considerations.
The six-radial "gull-wing" design seems to be effective, and IIRC there
was an article several years ago in QST about modeling such a design for
160 meters. Any model comparisons between buried and elevated radials
should be done with the double-precision NEC-4 engine which is not used by
most antenna modeling programs. EZNEC Pro/4 uses NEC-4, but you have to
pay an additional license fee.
There have been hundreds of posts about this subject on the Radio-Tech
e-mail reflector at Broadcast.net from engineers who have designed, built,
tested and licensed several successful elevated radial systems for
commercial broadcast use. A search of their archives can shed a lot of
light on this subject.
Ron N6IE
www.N6IE.com
----- Original Message -----
From: "Billy Cox" <aa4nu@ix.netcom.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Saturday, August 16, 2008 9:57 AM
Subject: Re: [TenTec] OT: Ground Radials at Tower Base
Sadly Derwin, you are very "missaken". Do a search
on W8JI, or read ON4UN's Low band DXing books to
learn how ground system really work.
There is "no free lunch" with radial systems.
73 de Billy, AA4NU
-----Original Message-----
From: Derwin Goliver <dgoliver001@woh.rr.com>
Sent: Aug 16, 2008 12:52 PM
To: geraldj@storm.weather.net, Discussion of Ten-Tec Equipment
<tentec@contesting.com>
Subject: Re: [TenTec] OT: Ground Radials at Tower Base
Well now....
As far as radials go. I like to mount my verticals off the ground.
Becouse just a few 1/8 wave off the ground. Is better than many in the
ground.
If I am not missaken. Some thing like 2 1/8 wave off the ground =
something
like100 in the ground.
I have a 5/8 wave 20 meter vertical with 3 off the ground (gound plane
style) . Thas I made this antenna is smoken' .
I mounted it on the garage roof in a tri pod. With 3 14 foot radials and
a
matching coil at the base.
Thing is this needs guys. Becouse of its 41 1/2 foot heighth .
Derwin
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
To: <tentec@contesting.com>
Sent: Friday, August 15, 2008 10:40 PM
Subject: Re: [TenTec] OT: Ground Radials at Tower Base
On Fri, 2008-08-15 at 19:46 -0400, Gary Hoffman wrote:
If you improve your grounding system, you will always be happy that
you
did.
To say it will or will not reduce noise requires knowing a lot more
about
the specific details of your setup.
The grounding system for a vertical antenna is often deficient. That's
easily seen when the antenna SWR is low, but there's no matching
network. The perfectly grounded vertical should have a feed point about
35 ohms. If the number of radials and ground rods is small, they can
contribute resistance to the feed point impedance raising it towards 50
ohms for a better apparent match. But with the radiation resistance 35
ohms and the ground resistance contributing half that much, the antenna
efficiency is 2/3 what it ought to be for both radiation and reception.
So improving the vertical antenna grounding (more radials, 50 is a
start, 256 is considered enough in broadcast circles, and more rods)
hurts the match but improves the antenna efficiency. That may actually
increase the noise heard, but it will increase DX signals by the same
amount so ought to be a wash. Unless a radial happens to contact a
ground from a noisy power pole.
If there are grounding issues (and maybe there are not) and you fix
them,
it
can certainly help.
The good noise reception on a vertical is why some 80 and 160 meter
DXers use a loop or Beverage for reception (directivity, not efficiency
is the goal) and the vertical only for transmission. Its hard to beat a
vertical for low angle (and thus best DX) radiation and reception, but
the propensity of a vertical to hear in all directions makes it hard
without going to an array of verticals to hear the weakest of signals
over the noise. Even atmospheric noise can be directional, so a
directional receiving antenna can be a benefit.
73, Jerry, K0CQ
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