On Thu, 27 Jun 2013 12:05:51 -0700, "Wayne"
wrote:
Needs to be either in the attic, or on a metal patio cover.
A vertical on top of a 20 foot pole "might" be possible.
Currently I am using a 1/4 wave vertical mag mount on top of a metal patio
cover. I also have a half wave dipole in the attic.
Are you doing CW and SSB at the bottom of the 6 meter band?
Or are you doing FM and repeaters in the middle of the band?
Or perhaps you are doing radio control at the top of the band?
Antennas for these purposes are quite different. For example, CW and
SSB is usually done with horizontal polarization, while FM and radio
control are done with vertical. I'll guess(tm) FM and vertical.
The most successful 6M FM antenna I've built was a simple center fed
vertical 1/2 wave dipole, with a balun at the feed point. Two egg
insulators at the ends. Cantilever supports projecting from a tower,
side of building, or tree to give some clearance. Coax run
perpendicular to the antenna wire. Distance from tower has a big
effect on the pattern, so I made the attachment point adjustable.
At about 9 ft in length, your attic might not be tall enough for a 1/2
wave dipole. You can bend the corners over and still have a usable
antenna. Loading coils will also shorten the antenna, but if you go
that route, do it symmetrically, with identical loading coils on both
wires of the dipole. If not, run it down the roof line at an angle.
The nice thing about this antenna is that it's very easy to build, and
then rebuild after you discover your calculations are not quite
accurate. Have a grid dip meter or antennal analyzer handy.
If you have the room in your attic, and you're always working
repeaters in one particular direction, you can build a "wire" yagi in
the same manner as the dipole. The driven element will look much like
the dipole, but the others are roughly 1/2 wave yagi elements. I've
build monsterious 2 meter rope yagis for transmitter hunts, but
haven't tried it on 6m.
If you do have a 20ft pole, and are concerned with aesthetics, try a
coaxial antenna. Basically, a 4.5ft large diameter 1/4 wave pipe over
the top of the 20ft pole for the counterpoise sleeve, and a stainless
4.5ft whip antenna on top. Use 75 ohm RG-6a/u coax to feed it, since
it's a 75 ohm antenna. The mismatch to your radio will be minimal.
http://www.belden.com/blog/broadcastav/50-Ohms-The-Forgotten-Impedance.cfm
http://www.solred.com.ar/lu6etj/tecnicos/En_75.htm
If a coax antenna is too much, try a 5/8 wave:
http://www.hamuniverse.com/6metervertical.html
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558