[Elecraft] KX2

[David Gilbert]

Yup ... that all makes sense.  The counterpoise as described by that 
link is at the antenna where it should be, and it compensates for the 
fact that the network can't produce an infinitely high impedance feed.  
I stand corrected.

Using the coax for a "counterpoise" is a really bad idea, though. There 
would essentially be no defined counterpoise.   There would be no 
control at all over what kind of balance the coax provides to the 
matching network at the end of the EFHW.  Length of the coax would have 
an effect, and not just the requirement for some minimum length ... the 
transmission line effect of the length would change its characteristics 
as seen by the antenna.  Proximity of the coax to nearby structures 
would also affect what the antenna actually saw.

73,
Dave  AB7E



On 7/14/2016 4:56 PM, Don Wilhelm wrote:
> Dave,
>
> All that is theoretical does not translate directly to the physical 
> world.
> Take a look at http://www.aa5tb.com/efha.html for more information.
> The counterpoise does not need to be very long, but it does need to be 
> present.
>
> If the coupling between the high impedance side of the matching device 
> is connected at the "ground side" to the shield of the coax, then the 
> coax shield can act as the counterpoise (with the attendant risk of 
> RF-in-the-shack), but does require some minimum length of coax to be 
> effective - the PAR EndFedZ is one example.
>
> 73,
> Don W3FPR
>
>
> On 7/14/2016 5:40 PM, David Gilbert wrote:
>>
>> I'm confused why an EFHW should need a counterpoise.  If it needs a 
>> counterpoise it isn't actually acting like an EFHW.  If it needs a 
>> counterpoise that means there isn't enough choking impedance at the 
>> feedpoint, and it means that the feedline is radiating with the 
>> counterpoise acting as ... well, a counterpoise.
>>
>> Manufacturers state a minimum length feedline simply to have the 
>> feedline losses help swamp out SWR variations along the line, and of 
>> course to marginally lower the SWR.
>>
>
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