UHF collinear antennas

[chuckinnc]

Has anyone had any luck with these? Ive trying to improve 800-1000 range with a better
antenna & have built several collinears from plans on the internet however when i check
them on Agilent RF analyzer at work the impedance & freq are way off.
Ive checked several factory mobile cell antennas and a few other factory uhf mobile antennas & they all check out properly on the analyzer. So has anyone had any luck building a high gain uhf vertical ?

 

[DaveH]

I heard this before, in fact it's happened to me before. I built a UHF collinear
as close as possible to the plans, and when I plugged in a receiver, signals
didn't get stronger, they disappeared. I could have made some error, but this
leads me to wonder whether some of these designs are reproduceable. Maybe
the guy who built it got lucky and didn't build more than one or two before
publishing the plans. Variations in materials e.g. diameter of tubing, coax etc.
could easily throw off tuning at 800MHz. Perhaps there are some "tweaking"
requirements that were found out later but never published. Building antennas
that work at those frequencies may look easy.

Reminds me of a UHF splitter/combiner I designed for 450MHz from
seamingly simple plans. Followed the dimensions closely, and measured
the return loss on an HP-10 at work. The center frequency was off by at
least 10%. I believe the PCB material (FR-4) dielectric constant variation
alone could have done it.

Dave