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
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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