I’ve had little success with various coax collinear attempts, including regular coax and also Andrew Heliax which just didn’t pan out in practice.
Here is another potentially easier way of creating collinear antenna’s…
ads-b-flight-tracking-f21/a-new-way-of-making-stripline-antenna-s-t36677.html
I’ll try applying some of the feed/matching suggestions outlined in this thread to see if it improves my initial build, which looks quite promising.
Nigel.