SWR Flucuations

[KC9ANI]

Running a screwdriver on my ford ranger pickup and have had no real problems up to now. Starting to see a flucuation of the swr on 40 meters and the wierd thing is that it is more pronounced in a certain neighborhood. I can drive to work and the swr will stay perfect. I run thru this one area (in Cincinnati) and it bounces all over and I have to retune. Sure wouldnt want to live in that area. Anyway, I'm getting ready to check all the grounds and make sure. Any thoughts??

[K0BG]

What you don't know is what's under the pavement you're driving over. Not only the surface, but the ground under the surface both affect the groundplane.

Some years back, the state of Texas tried to use glassphalt unstead of asphalt. Aside from how slick it got in wet weather, it proved to be a poor wearing surface. If you just happen to drive over some of the areas which still exist, you'll notice a great change in the conductivity between the two. And it will change the SWR as the groundlosses are much greater with the glassphalt.

Alan, KØBG

[KA5S]

I agree with Alan; ground can certainly affect antenna performance. However, it sounds as if you may ALSO have nearly resonant objects nearby, like lamp standards, poles and utility wiring, in the one neighborhood where your problem is most extreme.

Odd things can happen mobile.   In the late 1970's I was running a Ten-Tech Triton II mobile and noticing an odd warbling as I drove along. Turned out, if I even turned the car around the rig would change frequency. The permeability-tuned oscillator's ferrite core was being affected by the Earth's local magnetic field.  Even driving over re-bar in concrete roads would change frequency a few Hz.

Radio! You _never_ stop learning!

Cortland