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