DIY Coil Help?

[SirJ]

So I tried to apply some coil calculators I found online but was not able to find something usable for me. Anyways let’s get down to business. I have this Antenex TRAB phantom antenna. When purchased it did not come with a gasket between antenna *body and surface Nmo is mounted to. The threaded portion of the Nmo comes with an Oring inside. A disaster in design for sure, as a car wash system ripped this phantom apart but didn’t damage the vehicle. Unfortunately whatever was inside left too, leaving bottom half of Nmo still mounted and cap/ cup on the side of the automated system floor.

so down to the fun part, I have some solid copper, the diameter of a coat hanger (you know, the brass ones). I also have copper, brass and stainless springs and could kill the sprint retention and make a coil that way, I'd like to get at least 154mhz as it was before the explosion 💥 maybe even add a second coil for 490mhz too

 

[mmckenna]

This is what the UHF versions look like inside:




I think it's going to be a challenge to make a coil that will radiate worth a damn. There's going to be a lot of interaction between the roof of the vehicle and the coiled radiator, so coil calculators designed for rolling loading coils rather than a whip, is going to be off by some amount.

I'd probably start with 20" of wire and try it out.