Why adding coax changes swr

[Moleculo]

Using a tuner will probably allow you to present a good match to the radio for either 10 or 11 meters. That won't make it actually perform any better though. You need to figure out what the problem is and fix it instead of just applying a band-aid to it.

If you don't want to run ground strap, use a battery jumper cable to test with. Clamp one side onto the antenna mount and the other to something attached to the frame. You might have to scrape away a little paint on the frame side. If that solves the problem, you know that you need to run some ground strap.

 

[Beetle]

The only way to change the SWR is to adjust the antenna itself. A "tuner" has no effect on the system SWR; it only transforms it to something the transmitter can deal with as seen from the "tuner". The impedance ratio between the coax and the antenna doesn't magically change just because you're using a "tuner" at the other end of the coax.