Wim;
Thanks for your input, I just noticed that I had my finger on the
shift key when I posted the subject, so it came out as @0 meter.. :-)
I don't ever plan on running high power, 100 watts is about my
limit. I do want to stick to putting a vertical up. I have an old 1/4
wave 40 meter vertical that I was going to scrounge parts from.

Ken


On Tue, 24 Feb 2009 10:19:14 -0800, wimabctel wrote:

On 24 feb, 17:45, Ken Slimmer wrote:
Â* I was looking through some of my old antenna books and came across
Â* an
article from K6TS about building a 20 Meter Collinear antenna. Â*Has
anyone ever built one, or have any input on if it would be worthwhile
to pursue. Â*Weather is getting warm here, so I was looking for another
antenna project. Â*20 meters, vertical and ground mounted. Â*So I was
thinking about 1/2 Wave, 5/8 wave or the collinear.

Ken

Hello Ken,

I would not use the 5/8 wave antenna, unless you can make a dipole of
1.25lambda. The 5/8 wave vertical only gives the published gain over a
large good conducting ground plane. 3 or 4 quarter wave radials may
provide a reasonable floating ground for feeding the antenna, but it is
not a large ground plane.

Using a half wave has the disadvantage of the more complicated feeding
network. You may expect impedances up to kOhm range (depending in
thickness of the radiating element), so you need some high voltage
evaluation of your structure in case of 100W input power.

The advantage is the low requirement for the (floating) ground at the
feed point. Just 1 or 2 quarter wave radials are sufficient. These
radial wires may also slope down, as they carry low current, hence do
not have large influence on radiation pattern. When you have some
metal structure around you, you can use that as ground, eliminating the
need for radials. When you look to half wave CB antennas, most ones do
not have radials at all.

When you want to use horizontal polarization, a full wave center fed
dipole or 1.25lambda center fed antenna can be nice. Of course you have
to make something to rotate it….

When you want to design a vertical HW antenna from the ground up, I have
a document on my website dedicated to HW end-fed antenna design. It also
addresses high voltage issues.
http://www.tetech.nl/divers/HWmonopoleNL1.pdf. It is in Dutch language,
but all comment in illustrations and formulas is in English, so it can
be helpful.

Best regards,

Wim
PA3DJS
www.tetech.nl
without abc, the mail is OK.