[TowerTalk] 80M attic antenna
ccc at space.mit.edu
Tue May 20 18:19:56 EDT 2003
At 4:54 PM -0400 5/20/03, Dinsterdog at aol.com wrote:
>I have a rather large attic whereas height and space is reasonable
>to set up a center fed dipole. Can anyone suggest the best
>configeration for setting the antenna up for stateside ragchewing
>for around 3.900MHz +-200KHz.....
An 80-m dipole that close to ground is virtually omnidirectional, so
don't worry about what direction it runs. Just install it as high as
possible, with the centermost portion as high and straight as
possible. The ends, which don't carry much current and don't radiate
much, can be bent 90 degrees pretty much with impunity.
>and also, any food for thought experience with antenna style and feed?
You can't beat a center-fed dipole. Feed it with coax. I would put
a 1:1 current balun at the feedpoint.
If you have any wiring (e.g., for electric power, telephone, TV
antenna, alarm system, whatever) in your attic, put effective
common-mode chokes on all of it, because in the near-field of your
dipole it will be very closely coupled; it will raise your received
noise level, and your transmitted RF will play havoc with everything
electronic in your house.
Forget snap-on ferrite "beads." They have much too little impedance
to matter on 80 meters. Wind 12 to 14 turns of each cable on a
sufficiently large ferrite toroid, type 77 or 43. Yes, this will
probably require you to splice extra length into the cable.
73 de Chuck, W1HIS
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