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
----- Original Message -----
From: "Greg - ZL3IX" <zl3ix@inet.net.nz>
To: <topband@contesting.com>
Sent: Thursday, June 24, 2010 1:06 AM
Subject: Re: Topband: K3NA Loop Array
> Thanks for all the comments on this.
>
> Reading between the lines, I think I can assume the following. A
> Beverage over good ground will still work as well as over poor ground,
> *PROVIDED* that the ground is not so good, and the wanted signal levels
> therefore so low, that they are not able to override the receiver
> noise. The pattern and RDF and the same whatever the type of ground,
> and the unwanted atmospheric noise is lower by the same amount as the
> wanted signal. Correct?
>
> 73, Greg ZL3IX
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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