High Swr now.

[Tinman590]

Predator 10k copy, I had a 102 with a spring on a ball mount. Thought I would try a preadator 10k wanna be. Hooked it up and the swr went outta sight. Ran a ground wire to the frame from the mount. It is mounted on a aluminum toolbox. 97 f-250. No major deal I just wanna play around a bit.

[Tinman590]

Anyone know why the SWR would sky rocket like this? Thought It would be cool to try one.

['Doc]

Have you tried tuning it?
- 'Doc

[Tinman590]

Have you tried tuning it?
- 'Doc

Yeah I cut about 1.5 inches off of it, still the same.

[Tinman590]

still no good on my antenna

[Tinman590]

Ok surelly someone can give some advise or something. I have another 10k copy made by barjan, mounted to the ball mount where the 102 was. The swr goes past 3 and the 102 is flat. does this thing really require that much be cut off or something?

[626]

Ok Tinman,

Couple of things about your post. When you say skyrocket, what do you mean??

Are the readings higher on channel 40 or same across the board?

The ball mount adds about 2-3 inches of radiating surface to the antenna. So, if you are high on 40, then the mount may be making your antenna appear long.

my .02

['Doc]

Tinman,
There are a couple of things about loaded antennas that you need to keep in mind. The first is that the coil really ought to be above everything near it, such as the cab of the truck. That's because anything near that coil affects the field around that coil, so can change how it acts on that antenna, especially metal. The further away you can get that coil from stuff, the less it will be affected, and the less the tuning of that antenna is changed.
All antennas are affected by their length, no matter if they are loaded or not. Some lengths work better than others, tend to be resonant, which just means they radiate everything that gets fed to them. If the length of an antenna is increased because of how it's mounted, then you simply shorten that antenna back to it's resonant electrical length. If that ball mount adds something like 4 inches to the antennas length, then you gotta remove 4 inches somewhere else to keep it the same length as it was to start with. The "iffy" part of that is that reducing the antenna's length tends to be destructive, it's not very easy to 'glue' it back once you cut it off. Of course, that just depends on how you do the shortening, right? And that the antenna's original length was 'right' to start with! The antenna starts where the braid of that coax isn't surrounding the center conductor anymore, somewhere on that mount. If that antenna was designed or tested using a short mount (a stud mount for instance), and you put it on a 'tall' mount (ball mount for instance), then the difference in length has to come off somewhere to keep it 'right'. That can mean cutting off the stinger, OR, shorting a turn of that coil. Either/both shorten that antenna's electrical length. Of the two methods, shorting out a turn on that coil is the least destructive cuz you can remove that shorting wire/strap/whatever later. Just not as 'final' as cutting off that stinger. I'm trying to recommend some adjusting method that isn't going to totally trash an antenna in case that adjusting is in the wrong direction.
So, how about trying that shorting a coil turn to see if it makes any change in the SWR? If you happen to have a few extra stingers laying around, forget the coil thingy and try the different stingers! A very rough guess is that you probably have another 1.5" to get it close to what it ought to be for your particular mounting method. And please remember, that 1.5" is just a guess!
- 'Doc

(I tend to use a length of solder for a convenient, easy to use shorting conductor. don't throw it away when you're finished, you might need it later. And don't 'solder' it, just twist it on.)

(And it looks like Gunny has the same idea. )