[Antennas] Re: Linear Loading

2002年4月26日 09:25:07 -0400

At 08:39 AM 4/26/2002 -0400, Joe Giacobello, K2XX wrote:
>Sean, EZNEC is a commercial program available from W7EL at
>http://www.eznec.com/index.shtml.
>>However, speaking of linear loading, I would like to address a question
>to the other members of the list. Is there any any art or science
>associated with designing linear loaded antennas? Or is it pretty much
>a random process of simply compressing the dimensions of the antenna
>into the available space?
>>I searched the QST archives for articles on linear loading, but did not
>turn up much of any value. I know there was a design for a linear
>loaded quad back a few years ago. I am interested in some general
>principles, if there are any.

Joe and All,
It's just a length of the antenna folded back on its self, usually starting 
at the feed portion. It has the advantages of lower loss than a base 
connected inductor if you use 1" or so diameter tubing spaced 1' or so from 
the antenna, for a low band vertical. Also, the linear load part becomes 
part of the radiating portion of the antenna which of course a coil does 
not. The wire of the antenna its self can be used for a shortened dipole. 
I used 11' to 16' using 1" tubing spaced 1' in a triangle around the 
antenna, on a 45' top loaded 160-30 meter 4 band vertical I modelled, not 
built. EZNEC does a good job modelling the linear loading, if elements on 
the order of 1" in diameter spaced 1' or so. In my experience, it does 
less well if close spaced wire is used. I didn't notice that it broad 
banded the antenna any. There are a couple of brief examples in Low-Band 
DXing by John Devoldere, ON4UN. BTW, I have an extra copy of this book, 
like new. Cost 20,ドル sell for 10ドル plus shipping. It's also mentioned in HF 
Antennas for All Locations by Les Moxon, and in the 18th edition of ARRL 
Antenna Book. Dave Benson, K1SWL of Small Wonders Labs wrote up an article 
about a shortened HF dipole using linear loading in the winter issue NJQRP 
Home Brew magazine and presented a paper at Alanticon 2002 on it. There's 
probably some more references too. A good place to start is to look in the 
index of your favorite antenna book.
73, Chas, W1CG