> snowdrift problem described by W1FV. I want the feed point about
> 18-24" above the earth to avoid these problems... as opposed to "right
> at earth".
Every practical system will excite some small current on the outside
of the shield anyway no matter how the connection is made, because
the ground system is always less than perfect and the feedline is
always exposed to the fields from the antenna to some extent. This is
especially true if the feedline is elevated, or the radials are
relatively few in number (a groundplane with four radials normally
has substantial excitation of the outside of the shield).
Assuming you have a decent ground system, moving the feeder
connection up 1/250th of a wavelength would certainly NOT a major
cause of RFI or unwanted feedline radiation. This is especially true
if you dressed the cable down to ground at the feedpoint and ran it
underground or on the ground to the house.
If RFI isn't a problem and the shield ties directly to a good ground
system, you are probably all set.
If you have a poor ground or a sparse ground connection to the
shield, like only a few radials of any type, use multiple chokes. One
choke-type balun at the antenna and another where the feeder leaves
the general area of the antenna system would do the trick.
73, Tom W8JI
W8JI@contesting.com
|