Topband: K3NA Loop Array

[Greg - ZL3IX]

Thanks, Milt, that's what I thought intuitively. By "good -" and "not so 
good ground" I was also referring to the conductivity of the soil under 
the wire, not the grounding provided at the termination.

73, Greg

On 2010-06-25 03:28, Milt, N5IA wrote:
> Greg,
>
> If I understand your comment and question correctly, my answer is the 
> following.  These are my opinions based on the knowledge I have 
> obtained and the experience of working with Beverages for 15 years.
>
> You are correct that the pattern of a Beverage over good ground would 
> be nearly the same as the pattern of a Beverage over poor ground.
>
> You are correct that the unwanted atmospheric noise is lower in direct 
> proportion to the level of the desired signals.
>
> If the ground referred to in your comment "that the ground is not so 
> good" actually refers to the grounding provided for the termination 
> resistor at the far end and the grounding provided for the matching 
> transformers at the near end, then you are incorrect.  The grounds 
> really have very little to do with the gain and/or SNR of the antenna 
> itself.  Their purpose is to aid in the proper matching at the near 
> end for signal extraction and the swamping of the reverse signal at 
> the far end, thus rendering the design uni-directional.
>
> If the ground directly underneath the Beverage wire has high 
> conductivity, the effect is less signal voltage impressed into the 
> wire.  This can be compensated for by making the Beverage longer so 
> that more signal is accumulated at the near end.  The practical number 
> of wavelengths for a Beverage over high conductivity ground to achieve 
> useable signal level and at the same time not narrow the main lobe too 
> much is probably about 8.
>
> With poor ground and a low velocity factor of ground 1/2 of the 
> "transmission line" there is a practical limit of about 4-5 
> wavelengths that the Beverage can be extended before the signal delay 
> in the ground side reaches 90 degrees lagging the signal induced into 
> the wire.  After that, any lengthening of the Beverage actually 
> decreases the signal level although the pattern will continue to 
> become more narrow.
>
> Perhaps this explanation will help understand the relationship of 
> "good" ground vs. "poor" ground underneath a Beverage and how it 
> affects achieved signal levels into the RX coaxial cable.
>
> de Milt, N5IA
>