Colinear antennas
 

On Tue, 15 Dec 2015 14:40:40 +0000 (UTC)
Laszlo Lebrun wrote:


Is it allowed to post here a question related to antennas and without
crossposts? :-)

Reading the content of the other threads, I'm not quite sure...

OK let's try nevertheless:

A colinear antenna is using alternating sections if coaxial cable
whereas the signal is travelling half inside the coax, half outside.
The length of the sections should be half wave considering the
velocity factor of the used coaxial cable.

I would tend to consider the velocity factor only for the parts of
the antenna where the the signal is travelling *inside* the coax
cable.

I know, my reasoning is probably wrong, but why?

Thank you for your advice




Yes, I asked a similar question here recently as, like you, I had
questions and doubts about the actual workings of this simple aerial:

Message ID: 20151119002316.0a9bd48f@silent

The Owen Duffy links seem to confirm our suspicions!

I think that this aerial could be made to work with air-spaced coaxial
construction to eliminate the velocity factor problem we get from
co-ax cable, but mechanical problems would be more difficult and would
still require the plastic tube containing the aerial to be taken
into account. One piece of plastic tube could be quite different to
another...