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Old 04-01-2010, 07:03 PM
DC DC is offline
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Question Can a CB Antenna Be Cut Down In Length and Still Work?

I've got a Cobra 19 DX III CB along with a K40 CB antenna in my 2000 TJ. The K40 is a honking 55" long and when it gets whipping around off-road, it often contacts my hard top and rear windows and beats the hell out of them.

AFAIK, the very thin whip type K40 antenna is just a small diameter stainless steel rod with no wiring in the whip portion per se. If that's true, is there anything wrong with cutting the overall length down to say 36" and then having my CB retuned with a SWR meter? The reason I ask, is that a supposedly knowledgeable guy at my local Radio Shack told me today that it couldn't be done without totally ruining the antenna and thereby the performance of the CB itself.

If anyone has any knowledge about this (one way or the other), I'd sure appreciate hearing about it.

TIA,
Don
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Old 04-02-2010, 05:29 AM
Tumbleweed Tumbleweed is offline
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The short version is: You can cut it down, you will lose some performance and it may or may not be tuneable when you are done. It will likely be nothing better than a hot dog stick for the campfire.
Put a tennis ball over the antennae with a hole drilled in each end. That will space the antennae out from the top and give it some protection as a bumper. Or replace it with a 24 or 36" fiberglass antennae for around $20.
The K40 is a great antennae, I would not cut it up.
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Old 04-02-2010, 07:47 AM
DC DC is offline
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Thanks Don, and I have also gotten pretty much the same advice elsewhere to just forget about cutting down my K40 antenna.

A large part of my problem (beyond the 55" length of the K40 whip), is that my CB antenna mount is located up really high on my Hanson tire carrier. Here's a shot from the rear of my TJ that shows this:


As you can see, there's only about a foot of the base of the antenna before it clears my hardtop. Trying to use a tennis ball in that first foot is still going to leave the majority of the small diameter and very flexible stainless steel whip antenna above that point to still flail around (and I am not too keen on trying to otherwise tie the antenna down like some folks do).

By the way, the K40 hitting my top isn't so bad (other than the noise), but when it whips around and hits my side rear windows, it makes me wonder at times if it's going to hit just right one of these days (and with enough force) to finally crack one of them.

Anyway, based on this, it looks to me like I will probably be better served by just replacing my current K40 with a shorter antenna (and I see that there are some K40 Super Flex fiberglass antennas that are as short as 2 to 3 feet long). But I'll have to see how these shorter antennas can interface with my current K40 mount, because one of the things I like about my K40 is the 1/4-turn twist-off/quick-disconnect capability for quickly removing the K40 coil & whip assembly from the rear of my TJ.

Thanks again,
Don
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Old 04-02-2010, 03:15 PM
Tumbleweed Tumbleweed is offline
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I am a fan of the K40 mount and love the 1/4 turn twist off. I would still try a tennis ball at about the height of where your back glass meets the top-near the wiper. You can put some zip ties on it to keep it from sliding up and down on the antennae. You will be surprised at how much it will slow it down.
A rubber tip like a vacuum cap may help, too.
K40 may make an adapter to use their mount with a reg. fiberglass antennae-they usually have a 3/8 coarse thread mount.
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Old 04-03-2010, 11:35 AM
DC DC is offline
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After going round & round on this, I think I am going to stick with my current K40 for a while longer and see what I can do to potentially improve things with it (and that plastic vacuum cap on the tip is a great idea). Beyond that, I have come to the conclusion that the tennis ball approach will likely not work for my current set up. As you can see in this first side view shot, my K40 is already mounted with quite a bit of rearward rake:


And in this second shot, I am pushing forward on the whip about as much as I can without putting a bend in it, and it still isn't coming close enough to the upper rear edge of my top, such that a tennis ball in that position wouldn't even contact the top to initially help absorb some of the whipping motion.


So, I may mount the K40 base down lower so a tennis ball or stand-off bracket may be able to help. If that doesn't work, I may end up going with the shorter 2 to 3 ft K40 fiberglass antenna in the original mounting position on my Hanson tire carrier.

Thanks again,
Don
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