By Bob Catanzarite
Coax Cable Stripping - How To
I'll focus here on Quad Shielded coax here. With the 4 layers of shielding, it has the most elements to deal with. If your using anything with fewer shields the same principles apply.
The purpose of a shield is to surround the inner conductor with a protective grounding conductor. Shielding effectiveness is determined primarily by the conductive quality of the shielding material and the level of coverage the shield provides. Two materials are commonly used as shields - Braided copper and aluminum foil. Copper is a better conductor than aluminum. But, due to the gaps inherent in the braided copper construction, the level of coverage is lacking. The foil configuration used for aluminum provides more complete coverage but aluminum is not as good a conductor as copper. So most coax cables use combination of the two shield configuration to take advantage of the best qualities of each.
If combining braided copper and aluminum make a better shield then it follows that 2 layers of each will be even better. More is better right? So we have quad shielded RG6.
Here are photos of two Quad Shielded RG6 cables.
You can see especially in the photo on the right how these shields are layered around each other. You can also refer to Mark Henrichs page for more on this. Mark has some excellent information and photos on how these layers look.
One of the more frustrating parts of my project was not being able to find detailed instructions for how to strip coax cabling. I would have expected the manufactures of the coax connectors to have designed their connectors to work with some particular coax type that was stripped in a particular way. And that the coax connector suppliers would have provided some description of how to strip the coax to work with their connectors. These descriptions were not, to my frustration, in any of the places that I looked. Even the stripper that I bought and used had horribly vague instructions. So, by gathering bits and pieces of information here and there and trial and error this is what I came up with and used for my project.
Stripping coax is not difficult but does take some tool setup and practice. A must have tool is a coax cable stripper tool. You can strip coax cables with other tools that you already have but it is very difficult to control which of the shield layers you are cutting through. These coax stripping tools really speed up the stripping process and make it less prone to operator error and give consistent results. The stripping tools I have seen and used all have to be adjusted before they produce the right cuts on the particular brand of coax you are using. Different brands of coax have minor variations in thickness of the individual layers that make up the cable. These coax stripping tools have multiple cutting blades and each blade has to have it's depth of cut adjusted. This adjusting process is trial and error. And once you get your tool adjusted for a particular brand of cable it probably won't give you the right cut on another brand of cable - even thought they are both RG6 quad shield. This is a big incentive for you to use ONLY ONE brand of coax cable for your entire project. Hint - Buy your coax cable from a supplier that specifies the manufacturer and the manufacturers part number. If the supplier just calls it something like RG6 Quad Shield they may ship you Belden on week then Essex the next week. The point here is if you have to go back to that supplier to buy more cable you may not get the same brand and part number you started out with. Then you'll have to be adjusting your stripper tool every time you get to a different cable brand. Big headache!
You'll have to practice this stripping procedure using trial and error to get your stripping tool adjusted. But when you get the tool set right the job will go a lot quicker and you'll get better results.
These figures below show which layers of the coax cable that need to be cut. These are generic recommendations. Neither the coax stripper tool nor the coax connector I used came with details on how to strip the cable. If you are fortunate enough to get instructions with the tool or the connectors you are using then by all means follow those instructions. If not, follow these recommendations.
The figure above shows how the strippers cutting blades work. To properly strip coax cable for video connectors like the Type-F connectors commonly used in the home requires a 2 level strip. Now the strippers make both of these levels of strip or cut at the same time. Some strippers, like mine, are capable of making a 3 level strip as well. This simply means that they have 3 cutting blades. Because for our needs, we only need a 2 level strip, only 2 of the blades need to make cuts. This is where the adjustment has to be made to your stripper - the depth that the 2 blades cut to. This depth determines which layers of the shield get cut. In the figure above I am showing all 3 blades but have one blade shown as a dashed line to indicate how this blade should be adjusted so that it doesn't really cut anything.
The blade on the left should be adjusted so that it cuts through the jacket and the outer 2 layers of shield. The inner 2 layers of shield should not be cut by the left blade. Getting this left blade adjusted will likely take several tries to get right. The middle blade should be adjusted to cut through all layers except the center lead. Take a close look at the coax cable after you make a blade adjustment. The blade on the left should not be nicking the inner braided shield and the blade in the middle should not be nicking the center lead. Adjust the blade on the right high enough so that it doesn't nick the center lead.
You may wonder why we are cutting off the 2 outer shield layers. What good are they doing now? Well if you don't cut off these outer two layers of shield you will have great difficulty getting the coax inserted into the connector. The connectors just don't have the room inside for the cable WITH 4 layers of shielding on them. And the fact that we are cutting the very ends of these outer 2 shield layers DOES NOT diminish their effectiveness as a shield. These shield layers still provide shield coverage for the length of the cable run and all of the shield layers are in direct physical and electrical contact with each other along the length of the cable.
The last step before terminating or installing the connector is to fold back the inner braided shield and inner foil shield on to the outside of the jacket. Simple step here.
Important note here. Make sure that after the stripping process there a no slivers or pieces of the shield touching the center lead.
All this talk here makes this sound more difficult than it really is. A picture is worth a 1000 words. Follow the figures and make it easy.
Now your ready to terminate the connector on to the coax.