SWR meter inconsistencies

[undertaker]

Consider
this get a Stryker mag mount. Much better antenna.

 

[Handy Andy]

Surprised you have not figured out the 3rd Brake light and if there was a way to formulate a flat to "extend" that magnet to be more flush using the 3rd brake light housing and it's region of metal - being that is has extra layering and bolt threaded section and a cutout...along with that "shark fin" having a brace in that area to hold it in place - that is not just skin metal - there is a reinforcement in that area - as the Shark Fin would have some type of flange or cutout to seat and stay the OEM antenna in there with a gasket used to keep water out.

That region has a partly a "roll cage" design to prevent the crushing of the passenger compartment in the event of a crash and or rollover.

This area may also be why the SWR tended to improve - for you are using more metal passage for not just the skin-finish metal - but the reinforced region for crash protection.

Something to think about...

 

[Eldorado828]

I went out and took some pics of the antenna location just now. I keep worrying about it coming off where it is at, but when I grab the base and lightly attempt to move it I can see the sheet metal flexing under jt so the magnet does have a strong grip. But look at the slight overhang it has in the back. I feel like that could serve to let wind get under it and lift it off at 70mph. That’s about as fast as I ever go. Would you all let this worry you?

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Nah, don't sweat it, just run it. Placement looks like it will be fine but time will definitely tell.
Seems you've got it the best it'll do and for some reason that antenna looks to be very narrow banded with the way the wave rises at the ends. Just let her be and consider that the next upgrade should probably be a better antenna. Tram makes 2 mag mounts that are pretty good with the bigger one being best of the two, just a thought.