[Elecraft] Random wires

[David Gilbert]

That's a weird comment.  Barry and you both have it wrong, but you are 
correct that the radiation resistance is independent of the ground 
resistance.  The FEEDPOINT impedance, on the other hand is dependent 
upon both.

The radiation resistance is NOT affected by the folded element ... the 
folded element merely transforms the combination of the radiation 
resistance and the ground resistance to a different value.  The folded 
element does NOT change the relative magnitudes of the radiation 
resistance and the ground resistance, and therefore the folded element 
does NOT improve the efficiency of the system at the feedpoint.  It may, 
however, reduce transmission line losses by reducing the SWR on the 
feedline.

Seriously ... do some research first.  W8JI is a good place to start but 
there are others.

And by the way, Bill Orr made great contributions to antenna design, but 
more than a few of his works have since been proven less than completely 
accurate.

73,
Dave   AB7E



On 10/1/2013 2:43 PM, Ron D'Eau Claire wrote:
> I disagree. Barry has it right. The radiation resistance of the radiator is
> independent up the ground resistance. That's why a 1/2 end fed wire with
> it's very high resistance is highly efficient against a given ground system
> compared to a 1/4 wave long or less wire.
>
> Note we are speaking of a folded full-length (i.e. 1/4 wave long) element.
> Folding short elements to make up for electrical length is something else
> entirely different. The Orr twin-lead antenna that I remember was 125 feet
> long, making it a full 1/4 wave on 160.
>
> 73, Ron AC7AC
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Vic K2VCO
> Sent: Tuesday, October 01, 2013 12:44 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] Random wires
>
> Another way to look at it is that it multiplies the radiation resistance,
> but does the same for the ground resistance. So efficiency is unchanged.
>
> On 10/1/2013 12:40 PM, Roger D Johnson wrote:
>> This is NOT true! It merely raises the feedpoint impedance...just the
>> same as adding a
>> 4-1 transformer.
>>
>> 73, Roger
>>
>>
>> On 10/1/2013 3:10 PM, Barry LaZar wrote:
>>>
>>>      As I read your post, I infer that at the moment you are wanting
>>> to add 160 meters to your capability. An antenna that I have used and
>>> liked is the Twin Lead Marconi. It's a simple, cheap, and effective
> antenna. I first saw it written up by Bill Orr years ago.
>>> The premise of the design is that a quarter wave antenna driven
>>> against ground may not be the most efficient antenna due to low
>>> radiation resistance. Therefore, raise the radiation resistance by
>>> using the theory of a folded dipole. The folded element raises the
>>> radiation resistance by a factor of 4 for 2 elements as the impedance
>>> changes as the square of the number of elements. You will still need
> radials, but your ground losses will decrease.
>>>
>>> 73,
>>> Barry
>>> K3NDM
>>>
>>>
> --
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
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