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Unread 10-22-2010, 03:59 AM   #1
AlexGeorgakis
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CB cable length

So I've got my CB and I've got my antenna. How do I know what cable length I need to use? I know there's a formula somewhere about this.

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Unread 10-22-2010, 07:55 AM   #2
mylt1
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take a piece of rope, tie to your CB then run it along the same path you plan on running the coax to the antenna. when you get it where you want it and to the antenna mark the rope and measure how long it is.
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Unread 10-22-2010, 09:21 AM   #3
AlexGeorgakis
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LOL, no, that's not the way it works. Cable length has to be specific for the frequency and antenna size you are using. Too long or too short and you won't have correct performance. I need a formula or some sort of calculator where I can plug in my antenna length and frequencies and I'll get the exact cable length I need. You don't cut off the excess cable length. You have to loop it in a figure 8 pattern.
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Unread 10-22-2010, 01:43 PM   #4
Phreak480
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thats made up garbage. the coax doesnt have to be a special length and you can coil it up just dont make it too tight or you migrate the center conductor towards the outer braid and change the impedence. you actually would want to avoid certain lengths. having your coax an exact wavelength or multiple of can cause issues.

what you do want to do is find someone local who knows about cb and or amateur radio and has an swr meter to help you tune your antenna.
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Unread 10-22-2010, 02:09 PM   #5
97Formulaws-6
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There's no special length cables for CB radio or formulas, etc.

The only adjustment that NEEDS to be made is a SWR adjustment for your antenna.
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Unread 10-22-2010, 03:18 PM   #6
mylt1
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Originally Posted by ageorgakis View Post
LOL, no, that's not the way it works. Cable length has to be specific for the frequency and antenna size you are using. Too long or too short and you won't have correct performance. I need a formula or some sort of calculator where I can plug in my antenna length and frequencies and I'll get the exact cable length I need. You don't cut off the excess cable length. You have to loop it in a figure 8 pattern.
negative ghost rider, thats a bunch of malarkey. i have a general amateur license(working on extra) and can tell you, anyone who has told you that is full of it. keeping your run as short as possible means less line loss but in HF(which CB is) it really doesnt effect you that bad, plus im talking 100ft or longer runs,
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Unread 10-22-2010, 06:39 PM   #7
4wdjeepguy
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Usually for a mobile set-up you want to keep it around 18' and you can dial in the rest via the antenna from there. You shouldn't have that much if any excess cable if your running it from your radio in the front to the antenna in the rear.

And yes, I'm running 75' of cable on my base, but also, most base antenna's are set-up to self-adjust their SWR for whatever length of cable you are running. Setting up a base if diff from mobile
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Unread 10-22-2010, 08:11 PM   #8
SnowdogMarc
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Originally Posted by 20rubicon05 View Post
Usually for a mobile set-up you want to keep it around 18' and you can dial in the rest via the antenna from there. You shouldn't have that much if any excess cable if your running it from your radio in the front to the antenna in the rear.
Really?...I only needed 9' when it was in the center console and 12' when I moved it to the overhead console I built.

Use whatever length of cable you need to get from point A to point B and leave about 6-8 inches of extra for repairing connectors down the road.
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Unread 10-22-2010, 08:17 PM   #9
mylt1
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Originally Posted by 20rubicon05 View Post
Usually for a mobile set-up you want to keep it around 18' and you can dial in the rest via the antenna from there. You shouldn't have that much if any excess cable if your running it from your radio in the front to the antenna in the rear.

And yes, I'm running 75' of cable on my base, but also, most base antenna's are set-up to self-adjust their SWR for whatever length of cable you are running. Setting up a base if diff from mobile
dont know who told you that but they lied to you to. antennas do NOT "self adjust". they still need to be either trimmed to get a good SWR or you use an antenna tuner or are preset from the factory. even if they are preset they still need to be check once installed just to make sure its right.
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Unread 10-22-2010, 09:10 PM   #10
4wdjeepguy
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didn't know imax 2000s and antron 99s need to be trimmed. interesting...
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Unread 10-23-2010, 07:54 AM   #11
Phreak480
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any antenna would need to be tuned. theres plenty of "CB" antennas that just dont have any actual tunability built in though. and the 18" of coax thing is a bunch of junk. I've been a licensed amateur radio operator for a while now and have done countless antenna installs for various frequencies. also not all antennas are tuned by trimming some have other ways of being adjusted. the antron has rings that adjust the tuning of it for lowering your swr for example.
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Unread 10-23-2010, 09:58 AM   #12
AlexGeorgakis
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Hey guys, thanks for the input. This is all new to me. I've been told that the coax is essentially an extension of the antenna which is why it has to have the correct length in order to operate at it's optimal level. My CB has inbuilt swr but even after tuning I still had worse performance than others did with "correct" length coax. And it makes sense that the coax is an extension of the antenna since it's just a continuation of a conductor. Perhaps my problems arose from the fact that my CB wasn't connected directly to the battery resulting in more noise. That's all fixed now so I'll test it tomorrow.
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Unread 10-23-2010, 02:10 PM   #13
mylt1
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dont depend on built in SWR meters. get a real meter and test your antenna.
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Unread 10-23-2010, 02:14 PM   #14
mylt1
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Originally Posted by 20rubicon05 View Post
didn't know imax 2000s and antron 99s need to be trimmed. interesting...
those are pre=tuned but should still be checked with a meter.
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Unread 10-23-2010, 04:07 PM   #15
JChors
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Originally Posted by Phreak480 View Post
thats made up garbage. the coax doesnt have to be a special length and you can coil it up
Coiling can create an "RF choke". It's better to loop excess cable in a 'figure 8' as the previous poster said...
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