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Unread 07-22-2013, 10:27 PM   #1
VTEK1
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Pics of a K40 on your XJ???

I searched around but no one seems to use these anymore. I was wondering if I could use the trunk mount to a bracket off the side above the tailight, like most of us do. Just wondering if ya'll have pics or maybe some ideas for me. Much appreciated. Cheers!

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Unread 07-23-2013, 01:42 PM   #2
sAe23
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Antennas work best when mounted in the center of the roof. Mounted on a corner, up against the body of the vehicle, will make the antenna very directional.
If you don't want to drill a hole in the roof, or attempt to mount it to the roof rack, the next best place would be to use the trunk mount on the XJs lift-gate.
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Unread 07-23-2013, 10:18 PM   #3
VTEK1
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I have the trunk lid mount but don't have the two set screws and the rubber bottom, so I'm going to try and contact K40 direct and get replacements since I can't find them on the interwebs. I know that more then 2/3 of the K40 would be above the roof line so it wouldn't be too bad on the directional issue. Hopefully I can come up with something.
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Unread 07-26-2013, 06:59 AM   #4
KF4SQB
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I wouldn't suggest a trunk mount on the lift gate unless you have a metal-skinned lift gate. A fiberglass gate won't provide a needed ground for the antenna, and will break under the mount. sAe23 is correct; the center of the roof is the best place to mount an antenna for best performance. If all you're trying to do is talk to your buddies within a 1/2 mile or so on the trail, it won't matter much. Again, for best performance, hard-mounted is the way to go. If you want to use a mag-mount, ditch the K40, and get a Wilson.
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Unread 07-26-2013, 11:57 AM   #5
VTEK1
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Not ditching the K40 cuz it was free. Thanks for the info though.
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Unread 07-27-2013, 10:01 PM   #6
KF4SQB
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Quote:
Originally Posted by VTEK1 View Post
Not ditching the K40 cuz it was free.
I fully understand where you're coming from! You should've seen some of the home-brew antennas I've ran over the years, cause the parts to put them together were free. Any help you need with antenna/radio system setup, feel free to ask. I've been an Amatuer radio operator since '97, and have been playing with CB's longer than that. Best of luck!
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Unread 07-27-2013, 10:27 PM   #7
VTEK1
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I had to purchase the little black rubber plate and I'm going to try and fab up something to attach it to the side. If you are experienced with CB's maybe you wouldn't mind answering a few questions!?

1) is it really true what I said about as long as the top 2/3 is above roof line you should be good??

2) when using a magnet mount I always have to use my SWR to re-tune so is a solid mount better??

3) what would be the advantage to a wilson 1000 over a K40, I always thought they were very comparable?
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Unread 07-28-2013, 02:30 PM   #8
sAe23
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1: The K40 and Wilsons are coil loaded antennas, so unless the coil is above the roof line, you'll never get there...
2: Yes, but I've read that a lot of people have that issue with the K40 and not the Wilsons.
3: See #2 above, and maybe Google "Wilson 1000 vs K40" (Wilsons seem to handle more power.)
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Unread 07-28-2013, 02:49 PM   #9
VTEK1
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Ahhh duh, coil loaded should have figured that out. Well maybe if I don't like it ill sell it to someone and get myself a Wilson 1000. Thanks for the info! Cheers!
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Unread 07-28-2013, 10:08 PM   #10
KF4SQB
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To an extent, you are correct about the "2/3rds above the roof". sAe, I'm afraid that your statement isn't quite correct, as the coil, if properly designed and built (K40 and Wilson certainly are), radiates little to no signal. With a base-loaded antenna, as I'm assuming the K40 in question is, and as a Wilson 1000 mag-mount is, the "whip" above the coil does most or all of the radiating, with the majority of the signal radiating from the upper portion of the whip. For a center-loaded antenna, like a Wilson "trucker" series, there is some radiation from the short section below the coil, little to none from the coil, and the majority toward the top of the upper whip.

Antennas should be tuned when installed. Period. About the only exception is the full-size 1/4 wavelength (102") whip. There's generally no tuning provisions on those, and they are generally broad-banded enough to operate fine without tuning. A loaded antenna, be it mag-mount or hard-mount, needs to be tuned for best performance. If you're not looking form max performance, it doesn't really matter much. Just throwing it on there, with no tuning, should let you talk to your buddies on the trail a mile or so away with no problems. Despite popular opinion, running an untuned antenna will not damage the radio if you are running a stock radio. For mag- vs. hard-mount antennas, again, its a performance thing. The loading coil in a loaded antenna is used to make the antenna "appear to be" a 1/4 wavelength antenna from the radio's viewpoint. The 1/4 wave antenna uses the vehicle's body to make up another 1/4 wavelength, effectively creating a 1/2 wavelength "dipole" antenna. This is why its better to mount an antenna in the center of the roof. Mounting off-center "skews" the radiated pattern of the antenna, which should be "doughnut-shaped". With a loaded antenna, the body is still used to make up the other 1/4 wavelength the antenna needs to create a 1/2 wave dipole. With a mag-mount, you are "capacitively" coupling the antenna's ground to the body, which is not as effective as directly attaching the antenna's ground to the body. This is a pretty technical field if you get too deep into it; I'm trying not to get too deep and too technical. Also, just FYI, the popular 4' CB antenna, about the diameter of a finger, is whats known as a continuously loaded antenna, as the loading coil pretty much is the antenna, and runs from top to bottom. This is about the only situation where a properly designed and constructed loading coil radiates.

As for the Wilson .vs K40 issue, its a quality thing. Performance-wise, you probably won't see much, if any difference, aside from power handling capability. If you're running a stock radio, its a non-issue. The Wilson's are just built a little better, thats most of it. Don't get me wrong, the K40 is a good antenna, and is miles ahead of a lot of other antennas on the market. For the price you got it for, I'd run it, too! Of course, that being said, I'm running a 102" 1/4 wave whip, mounted on the left rear quarter, just above the "cut-line" that runs down the side of the body.
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