[Elecraft] BL-2 Connection To An Unbalanced Wire Antenna

[Steve Ellington]

Don
I'm running a special on RF grounds today. I've carefully measured out some 
1/2 wave wires, cut out 6" from the midpoint and offering these for $25. 
This will totally eliminate the need for multiple radials.
Happy April 1.

Steve Ellington
N4LQ at carolina.rr.com
----- Original Message ----- 
From: "Don Wilhelm" <w3fpr at embarqmail.com>
To: "Ron D'Eau Claire" <ron at cobi.biz>
Cc: <elecraft at mailman.qth.net>
Sent: Wednesday, April 01, 2009 6:12 PM
Subject: Re: [Elecraft] BL-2 Connection To An Unbalanced Wire Antenna


> Ron,
>
> I have been preaching similar points in ham circles for years now - and
> I find that many hams cannot visualize the difference between a
> "ground"  (meaning a return path for current) and Mother Earth.
> Actually any point where the RF current crosses the zero voltage point
> is a point of RF Ground (it is a potential, not a physical place), and
> on a balanced antenna it should occur midway between the two sides of
> the feedpoint - and a vertical with radials *is* a balanced antenna,
> that is why a balun is needed even on a vertical.
>
> The English do distinguish between "earthing" and "grounding", and I do
> wish that sort of distinction were also in common use in the US, it
> certainly would help.
>
> BTW - elevated radials *do* radiate in the very near field, but when
> arranged properly (pairs in opposing directions), the radiation is out
> of phase and will cancel at a distance from the antenna.  Your term
> "current sink" is not a description I would use.
>
> 73,
> Don W3FPR
>
> Ron D'Eau Claire wrote:
>> Jim, IMX it's a mistake to equate "RF ground" with an Earth connection.
>>
>> An RF "ground" is just a low-impedance, low-reactance current sink for 
>> RF.
>> Of course it is an integral part of the antenna circuit.
>>
>> An RF "ground" would not be expected to radiate, and most "counterpoise" 
>> or
>> "radial" setups don't radiate a significant amount of energy*:
>>
>> 1) Counterpoises near the Earth and on-ground "radials" tend to couple 
>> all
>> their energy into the lossy dielectric of the Earth, never to be seen 
>> again.
>> This is how BCB stations achieve a good RF ground generally using 120 0.2
>> wavelength radials around their towers to couple the RF into the Earth.
>>
>> 2) Elevated radials will radiate a lot unless they are carefully balanced
>> and symmetrical so "legs" produce RF fields that cancel each other 
>> outside
>> of the immediate area of the antenna. Such radials, like any RF ground,
>> *are* part of the antenna circuit but, when properly designed, they are a
>> non-radiating "current sink". In the common "ground plane" designs, they
>> also decouple the radiating element from the feed line, providing an RF
>> "ground" not only for the radiator but also grounding the feed line at 
>> the
>> antenna so RF currents don't flow down the outside of the coax shield.
>>
>> Ron AC7AC
>>
>>
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