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Old 01-06-2014, 08:42 PM   #1
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How to test a coaxial cable.

I have seen some posts about trying to fix various TV reception problems and thought this might be helpful. This technique works for any kind of coax cable, CB, TV, Satellite or what ever.

You've probably figured out you will need a multimeter that can read resistance in ohms. And you'll need to run to Radio Shack for a few other things.

Let's start with CB radio style coax, because that is simpler. You will need a 5 watt, 50 ohm CB "dummy load" (the Radio Shack clerk may be clueless) and a barrel adapter. The dummy load is male and so is the cable end. Thus you need a female/female barrel adapter. The dummy load is about the size of the end of your thumb.

Disconnect the cable in question at both ends. Install the barrel adapter/dummy load at one end. Now at the other end of the cable measure from the center conductor to the outer layer, the shield, of the coax. The meter should read about 50 ohms. If way less, the cable is shorted. If way more, then the cable is "open".

Now for TV coax. The same type of device is called a termination resistor or simply a terminator. It's resistive value is 75 ohms and it looks like an "F" cable connector with the cable end closed up. You will need an "F" style barrel connector here, too. Attach the terminator to one end of the cable and measure from the other as above only now you should see 75 ohms not 50.

If there is a splitter in line somewhere you could see a short or an open when you measure your resistance, depending on the type of splitter. Be sure you are measuring nothing but cable. No splitters. You should see about 75 ohms.

Terminators are also useful for improving signal quality. Unused splitter ports should be capped off with a terminator. Long story (about impedance matching) short, more signal is delivered out to the TV if the splitter is properly terminated.

This technique also helps in sorting out multiple cables. Only the cable you put the terminator on will show 75 ohms. To make sure, take the terminator off and measure again and see a high resistance or open.

Set top boxes put a DC voltage on the center conductor, so don't mess with the cables with power applied. Also, only certain kinds of splitters will pass the DC voltage. You can tell by the expensive price tag. The wrong splitter will kill power to your outdoor unit.

Hopefully you got all that and find it helpful.
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Old 06-29-2015, 06:32 PM   #2
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Great information.. but one question. I need a new coaxial cable to hook up from the camper to the campground cable. I see 20ft cables from $6 to $160. What do I need and what should I look for in buying a cable? Thanks!!!
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Old 06-29-2015, 07:11 PM   #3
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CE TECH 25 ft. 18-Gauge RG-6 Quad Shielded Coaxial Cable-RG6-MPP-25B - The Home Depot

This is indoor/outdoor low loss cable. Get this or similar. About $15
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Old 06-29-2015, 07:18 PM   #4
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Cables with 'gold' connectors are just hipe....Lowes 50' white RG6 works just fine. So called 'monster cable' is a waste of money.
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Old 06-29-2015, 08:08 PM   #5
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Thanks, so I do not need go with the real pricey cable.
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Old 06-29-2015, 08:14 PM   #6
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Quote:
Originally Posted by Missdenise View Post
Thanks, so I do not need go with the real pricey cable.
No you do not.

I carry three different lengths of coax the longest one is what I pulled off the house after we booted a dish company.
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Old 06-29-2015, 08:18 PM   #7
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Also pick up a couple (usually 2 to a package) push-on coax cable adapters as screwing on the coax is a pain in the neck.
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Old 06-29-2015, 08:28 PM   #8
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Also pick up a couple (usually 2 to a package) push-on coax cable adapters as screwing on the coax is a pain in the neck.
I've tried those that Radio Shack handled and although quick and easy, gave me really poor reception.
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Old 06-30-2015, 08:08 AM   #9
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Great post radio. Thanks!


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