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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>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>
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