High SWR - Cobra 29LX w/ magnetic mount antenna

Well they sort of do, I think the problem is with the mount at the base is isolated from the bottom (magnet) part.

Now as I said it is difficult to figure it out so your patients is really important.

If I was there, I would spot the problem in a matter of minutes but I am not so I have a suggestion, seeing you are down there in Myrtle beach SC, and maybe near Hwy 17, if you know where harbor freight is, I would suggest getting a cheap multi-meter (link below) that can help you with checking the setup.

Here is what I would do with it.

I would do what rabbi posted with the image, check the connection from the radio to the antenna to see if there is nothing connecting the two. Then I would check to see if there is no open wire between the two by shorting out the antenna mount studs to each other with a piece of wire, and if this shows a short, it is alright so far so put it back together. Then see if you have a connection between the stud under the foil and the foil itself because you need that. If it isn't, then there is the problem because it needs to have that part of the ground to connect it to the foil to make the capacitor work.

Now you can skip the first two parts and go right to the last part (checking the foil and the stud on the bottom.

The multimeter is about $6 or $7 - I think it is on sale.

7 Function Digital Multimeter with Backlight

 

Just a note... I just installed a new radio in my car and bought a Lil Wil mag mount to use with it. The antenna is incredibly narrow banded and the SWR was at 2.5 right out of the package. Raising it just a half inch or so made the SWR shoot up between 3 and 4.

I ended up trimming about a half inch off the whip and bottomed it out in the base to get 1.29 at 27.185 mhz.

 

Is the antenna bottomed out in the base? Raise it 1/4 inch... does the SWR go up or down?

Check SWR on channel 20. If it goes up, trim 1/4 inch off the whip, reinsert until it bottoms, then recheck SWR. Did it go down? Great, keep trimming 1/4 inch at a time until the SWR starts to go back up. At that point, you should be able to raise or lower the antenna in the base until you get the lowest SWR.

You can see by the graph I posted, what SWR looks like. I have mine centered at 27.185 mhz (channel 19).

Raising the antenna, or making it longer, causes the low point to be at a lower frequency (channel).

Lowering the antenna or making it shorter, cause the low point to move up in frequency.

Without getting too complicated on other factors, your radio will be happiest when that low point is centered in the channel you talk on the most.

If you don't have a fancy antenna analyzer like I have, you can make your own graph by plotting the points on a sheet of graph paper. Start at channel 1, note the SWR and record the point on the graph. Do this for each channel up to 40 and then connect the dots. You should see something like the screen on my analyzer shows.

 

If that bottom stud is connected to the shielding of the coax, then it would probably work. Use a SHORT braided flat ground strap from the stud to the tool box. And then another short one from the toolbox to the bed.

Don't be tempted to use regular wire. It can radiate and act like an antenna.