Collinear
This antenna design is better suited for people who don't have the expensive equipment needed for fine-tuning.
Just build it to the exact specs, put it into a PVC pipe (some call it a 'radome') and it works.
A copper wire 3mm wide is what I used. I also added two spacers (to prevent it from touching the radome). These spacers are placed where the intensity of the wave is minimal. (see the picture below)
The dimensions are slightly different from you may find on the web.
This one was fine-tuned to be used in a 50mm PVC pipe and these are the final dimensions!
It works fine. Its expected gain is about 5.5dbi.
In my design, I combined this antenna with a low-loss filter (<0.5db) and a low-noise (12db gain; NF<1db) amplifier. Thus I can use a longer RF cable without losing sensitivity.
The antenna amplifier is powered via the coaxial cable. If your receiver doesn't have this option, you may provide it yourself.
This is the final assembly.
Below the antenna itself there is the coaxial cavity filter, and at the bottom there's the antenna amplifier.
The jagged non-metal things on top of it should dissuade seagulls from perching on it.
The PVC pipe is sturdy enough and using braces this antenna may be fixed to a chimney (for example), but the braces must be below the the ground plain wires, and the upper part of the assembly (above the ground plane wires) should not be obstructed.