# Colinear Vhf antenna

Textbook colinear vertical antenna designs show coax cable with alternating braid to centre configuration. Commercial whips seem to utilise a single wire as the radiating element with .66 velocity factor phasing shields along the radiator with no other connections.

How does this work? I can copy the design but am intrigued as to the theory behind it.

Also how do you feed the antenna? A 1/4 wave stub like a j-pole (or something else)? This has to be up in the weather, so simple and robust is better!

I'd explain this better with diagrams but I don't know how to put up a picture?

• To add a picture, click on the sixth icon in the toolbar above the text entry area - the square icon that looks like mountains and sun. Click the "paste" link to insert a picture from the OS clipboard. Jun 18 '19 at 8:45
• I'm confused by the comparison between a coaxial collinear and a "commercial whip." Please point us to examples of each for reference. Jun 18 '19 at 17:15
• I mean the fibreglass pole type as seen for mobile and base station use where the radiating elements are enclosed, rather than the steel whip types where loading coils etc an be seen. Ie: 1/4 wave a loading coil then 1/2 wave on top. The enclosed fibreglass poles seem to use one continuous conductor up the centre, threaded through tubing of 1/2 wave x the velocity factor as phasing elements. Searching for ideas on line I see numerous references to lengths of coax cable with the inner and outer conductors reversed every 1/2 wavelength. How did the first example evolve from the second? Jun 19 '19 at 9:01
• coax cable with alternating braid to centre [conductor]? It sounds like you are referring to a coaxial Franklin antenna. Jun 20 '19 at 18:37