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This article is inspired by a conversation I had over at the Satellite Guys forums. Satellite Guys is a great place to ask questions from people with a variety of differing experiences. You'll get certified installers, long-term DIYers, and everything in between. I would love to say that you could get all the support you need from reading this blog, but if you can't, it's another resource to look at. Over the years, the staff at Satellite Guys have been very friendly to this blog as well.

But enough of the introductions. Let's get down to business

Voltage loss in RG6 cable

It's important to know that compared to the wires in your walls, RG6 cable isn't terribly good at carrying current. The center conductor is very thin — typically 18AWG. A little research reveals that you can typically expect the wires in your wall to be 12AWG, which is quite a bit thicker. Thicker cable loses less current over distance, it's that simple.

RG-6 cable is used to carry current to satellite dishes, antenna preamps, and a lot of other RF equipment. So the question comes up all the time: how long can the cable run be before you lose too much power? It's a surprisingly difficult question to answer.

My expectations vs. real world testing.

First of all, I was taught by older DIRECTV documents that when planning for current loss, to expect one volt lost per 20 feet. Others have said that's way too conservative and that the actual number should be about one volt lost per 50 feet. So, I set out to test what happened in the real world.

It's worth pointing out that these real-world results are really only valid for me. They give you one result that happened in my specific testing conditions. Your results may vary, especially if you are trying to send a different about of current down the line than I am.

Test parameters

For this test, I supplied voltage over coax using a DIRECTV 29 volt power inserter. As you'd guess from the name, this device is rated to supply 29 volts at a maximum of 1.4 amps. This particular one was brand-new in box. To test, I connected a 1.5 foot jumper of Solid Signal Dual Shield cable to it. Using my trusty Craftsman multimeter, I measured an actual voltage of 29.9 volts. A little hot, but not a problem.

I then used a 33-foot length of Solid Signal Dual Shield Cable and measured the voltage at the end. This cable has a solid copper center conductor and is DIRECTV-approved. At the other end I measured 28.7 volts.

Finally, I used a 25-foot length of what I'll call "crap cable." It's cable that came with a low-end antenna I was testing. I doubt it conforms to the RG-6 standard and I'd be really surprised if the center conductor was solid copper. I didn't dissect it to check, but I'm pretty confident of its poor quality. At the other end I measured 28.1 volts.

Results

A little algebra later and I came up with some relevant results.


As I said, every situation is going to be different. Additional testing with longer cable lengths would have probably also helped fine-tune the results. However, for a quick and dirty comparison with the cables I had lying around, this does tell me something.

DIRECTV's estimate of 1 volt per 20 feet is pretty conservative. I expect that if I had tested on a longer cable run, I would have gotten a number closer to 1 volt per 35 feet.

On the other hand the "crap cable" performed even worse than expected. Losing 3 volts is a pretty big deal, that's 10 percent of your voltage in only 25 feet. You have to wonder what else that cable is losing as well. At some point I'll have to do a comparison using it and check signal levels and the signal-to-noise ratio, just to see what I get.

The bottom line for your DIY project

As you do any DIY project, it's always a good idea to check your results against what you expected. Not every device will tell you its absolute minimal voltage. Most devices will work even if they are under voltage. They may not work as well or last as long, though.

It's a good idea to measure current levels where you plan to connect something, to try to get an idea of what your overall loss has been. DIRECTV equipment will work with significantly less than 29 volts, quite happily. In fact when powering the dish, the dish is not likely to fail unless the voltage at the dish is under 16 volts. Even assuming one volt per 20 feet of cable, that means you could in theory be 200 feet from the dish and still powering it properly. (The standard for installation is 50 feet.)

More questions? Call the experts at Solid Signal! We're here for you during East Coast business hours. Call 888-233-7563 to get a trained technician on the line. If it's after hours, fill out the form below and we'll get right back to you.

The post How much voltage do you lose over an RG6 cable? appeared first on The Solid Signal Blog.

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