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Re: [TowerTalk] Floating Elevated Radials

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Floating Elevated Radials
From: K4SAV <RadioIR@charter.net>
Date: Sat, 30 Dec 2006 10:47:38 -0600
List-post: <mailto:towertalk@contesting.com>
DON'T ISOLATE the radials of your vertical from an earth connection.  
This would be a disaster waiting to happen, both for safety and 
lightning protection. Tying your feedline into your tower ground system 
would be the best way to configure this. It should also be tied to 
ground at your entrance panel and to the safety ground at your station 
just like the grounds for all other antennas.

The amount of RF current you have going down this connection does effect 
efficiency slightly. If you don't have a ground connection (and no 
balun), that current would be conducted on the feedline as common mode 
current and would contribute to feedline radiation and RF in the shack.  
The amount of current that can exist on a ground connection (or the 
feedline) is a function of how many radials you have, and whether or not 
the ground system (or feedline) happens to be resonant. Bottom line is 
that the effect on efficiency is NIL unless you only have a very few 
elevated radials and the ground system happens to be resonant.

It's interesting to note that even with a good ground and a balun that 
you can't prevent all feedline common mode currents.  The field coupling 
from the antenna will put currents back onto the feedline even if it is 
perfectly decoupled at the antenna connection. This is the reason you 
sometimes hear the suggestion of putting chokes a half wave away from 
the antenna. However this is rarely required, except maybe when the 
feedline happens to be a resonant length. Grounding is the same 
situation, you can't prevent all ground currents even with elevated radials.

Jerry, K4SAV

Phil Clements wrote:

>  
>
>>Subject: Floating Elevated Radials
>>
>>
>>    
>>
>>>In transmitting systems elevated radials should never have a ground path.
>>>Grounding elevated radials reduces efficiency.
>>>      
>>>
>>>If the house has a lot of noise and you receive on the transmitting
>>>      
>>>
>>antenna >you might not want to directly ground the antenna ground system
>>to the >house. This is especially true with a small radial system.
>>
>>    
>>
>>>73 Tom
>>>      
>>>
> My elevated radials float, and are connected directly to the shield of the
> feed line. (7/8 inch Heliax.)
> 
> When the other end of the Heliax is connected to the output of my amp, it
> is "grounded" to the "house" central grounding point because the chassis
> of the amp is strapped to it. Are you saying that the amp and transceiver
> should be isolated from "house" ground also? If so, just how much
> efficiency is gained?
> 
> It has always been common practice to DC ground the radials of a ground
> plane antenna via the tower and its ground rod system, and by strapping
> the shield of the coax to the tower ground system at the base of the
> tower. Are you saying this method has less efficiency? If so how much
> less?
> 
> (((73)))
> Phil Clements, K5PC
>  
>
>>    
>>
>
>
>
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