antenna manfactures coax requirements

You HAVE TO have 18 feet of coax,this is a starting point for any antenna used for the CB band. Now you can run a longer coax if you need to as long as you do it in 3 foot lengths,if you do it this way your SWR will be easier to set,other wise you will be chasing your tail with and odd length of coax. You can order a cheap SWR meter on line or find one at Radio shack. If you don't have a cb shop close to you you need to do this because if you don't and your SWR is to high sooner or later you WILL blow the finals out of your radio!

No disrespect to you but if your not going to do the install right then don't do it at all because in the end it only its only going to cost you money and aggravation!

 

I was taught to use as much coax that is needed to reach your antenna, if the length of your coax effects rhe impedance of your antenna system you might have other issues.

 

CORRECT .....

You cannot tune a antenna using coax UNLESS the coax is not 50 ohms then it is acting like a matching stub ....

 

The standard type of coax for a single antenna setup is RG 58. RG 8 is an upgrade from RG 58 ;therefore, RG 8 is a better grade of coax. A little overkill for a stock out of the box cb radio with no additional amplification but perfectly acceptable.
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The coax has to be long enough to connect the radio to the antenna. 18 feet of coax is a common myth. It is based on the 1/2 wave length of the cb radio frequency which is 18 feet. What these people fail to realize is that 18 feet is the 1/2 wave length of the cb frequency through air. We connect our cb radio to the antenna using a coax cable. The cb radio frequency is traveling through the metal wire that is the center conductor of the coax cable. The 1/2 wave length of the cb frequency traveling through metal, ie the metal wire center conductor of the coax cable, is 11 feet 10 inches. So, that 18 feet of coax cable is actually over 50% longer than the applicable 1/2 wave length of the cb frequency that travels through the metal center conductor of the coax cable being used. Okay, in plain english, the half wave length of the cb frequency has absolutely zip, zero, nada, nothing to do with the coax length. Use whatever coax length you want. If it is long enough to connect the radio to the antenna, you are good to go.
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I do suggest that any excess length of coax be fashioned into a figure "8" approximately one foot in length.
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In case someone not familiar with standing waves is reading this post now or in the future, I state the following. Not using an SWR meter to determine the standing wave ratio or SWR is, in my opinion, a mistake that can seriously damage your radio. If the SWR reading is 1.1 that is a perfect score you cannot do better. 1.2 or less is like an A. 1.3 or less is like a B. 1.4 or less is like a C. 1.5 or less is like a D.
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It is a common misconception that a SWR reading higher than 1.5 means that you need to tune the antenna. WRONG, WRONG, WRONG. If the SWR reading is between 1.5 and 3.0, you probably need to tune your antenna. However, if your SWR reading is 3.0 or higher, that indicates a CONNECTION PROBLEM. Common connection problems include breaks or shorts in the coax cable, breaks in the internal wire of the antenna, faulty antenna ground among things. If you have a SWR reading of 3.0 or higher, do not use the radio or you are very likely to damage the power transistors, commonly refered to as "the finals". Should that occur, you will be lucky to be able to transmit a quarter mile if that far. Fixing a radio with blown finals is quite expensive. Getting your SWR checked is cheap insurance and money very well spent.
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If you are a total novice to CB radio, it is time well spent to go to the local library and check out a book on CB radio. Purchasing a used book on CB radios that you can use and reference is also money well spent.

 

I think you mean higher than 3:1 in the part highlighted in red, you should edit it so it's not confusing. Calling 1.5:1 a "D" makes it sound like there's something wrong with a SWR of 1.5:1.

"They" are telling you to use 18 feet because that's what "they" have always told them, and "they" don't know any better.

 

Some Manufactuers made or sold coax. So maybe it was said to boost their bottom line. If your 9ft 8x works for you. By all means use it. I've run 9ft of 8x coax for years. And everything worked just fine. It's true you only need the amount to reach for antenna to the radio.