Which RG-6 Satellite cable features are important, and which are not?

[JimBobStPaul]

Hi.

My questions are all about specific variations of RG-6 in satellite receiver systems: what features are required by code, and what are recommended because of technical considerations. I understand these may not always match. ;^)

There are two questions; both assume use in a normal single-family residence with standard electric utility service, and thus using the "Grounding Electrode System" (GES) appropriately. My questions have _nothing_ to do with how the grounding is done; we are assuming that it's grounded properly as the RG-6 (with ground, of course) comes from the dish/LNB and enters the house.

1. _After_ being properly grounded at house entry, for the entirely-indoor run to the Satellite receiver, does NEC require RG-6 _with_ground_, or is there some other reason I may want the ground wire?

2. For all RG-6 runs in satellite receiver systems, indoors or out, with ground or not, some supposed experts say "just use quad-shielded; the extra cost is worth it" or "quad-shielded is the industry standard", while other experts say something like, "if it's decent quality, 100%-shielded, with reasonable braid coverage over 100% foil, that's all you ever need in a normal residence". Please tell me your opinion, and with it please refer me to some technical report, e.g. comparative performance of different styles of shielding in actual satellite receiver systems, that explains why. I am very well able to read and understand very technical discussions.

Thanks for any help.

JimBobStPaul

 

[petersonra]

I would not worry all that much about grounding. As long as you do it to code it will suffice for whatever it does.

As for whether one brand or style of coax is "better" than another I think you will find a bunch of different thoughts on that. Certainly there are differences between various coax cables but my suspicion has always been that the quality of the connectors and how they are made up are probably a lot more important to system performance than the actual cable.

if you are using the cheapest connectors possible and making them up with a pliers type tool, you probably will not see any benefit to a "better" coax.

 

[hbiss]

The ground wire (really the messenger on RG-6 Fig 8 aerial cable) only runs from the dish down to the ground on the ground block, which you stipulated is properly grounded. You use regular RG-6 after the ground block.

As for which cable to use- Dish and Direct TV both provide their installers with a list of accepted manufacturers and type of cable that they must use along with connectors. I have no problem with "decent quality, 100%-shielded, with reasonable braid coverage over 100% foil". Decent quality means Belden, Commscope or equal. I like to see it swept to 2Ghz.

Beyond that, this isn't a satellite or satellite installer forum if you need technical reports, opinions, etc.

-Hal

 

[JimBobStPaul]

Thanks for the helpful (and quick!) responses.

So, just to confirm that I understand:

There is no reason, either (1) because of NEC or (2) because of any technical consideration, to use RG-6 _with_ground_ (as opposed to without ground wire) on the indoor cable runs from the properly-grounded house entry to the satellite receiver; correct?

 

[LarryFine]

Thanks for the helpful (and quick!) responses.

So, just to confirm that I understand:

There is no reason, either (1) because of NEC or (2) because of any technical consideration, to use RG-6 _with_ground_ (as opposed to without ground wire) on the indoor cable runs from the properly-grounded house entry to the satellite receiver; correct?

Correct. The cable shield [provides all the "grounding" needed.

 

[hbiss]

Plenty of places on the net that discuss how to do your own dish installation.

-Hal

 

[Cow]

I've heard to choose a cable with a solid copper core over the copper coated steel type, but have never followed up to know if it actually makes a difference or not??

 

[hbiss]

Good point, one I forgot. Yes it does make a difference if you are powering equipment like an LNB or multi-switch through the cable. You want solid copper, not copper clad to minimize voltage drop. So add to the cable specs: solid copper center conductor.

-Hal

 

[ggunn]

Good point, one I forgot. Yes it does make a difference if you are powering equipment like an LNB or multi-switch through the cable. You want solid copper, not copper clad to minimize voltage drop. So add to the cable specs: solid copper center conductor.

-Hal

Something I have always wondered about - why doesn't TV cable use two center conductors carrying signal and inverted signal the way that sensitive audio circuits do? No shielding is 100% effective and common mode rejection could help deal with what gets past it.

 

[hbiss]

The only balanced transmission line I have ever seen is 300 ohm twin lead and that was never good at rejecting interference. It had to be twisted to help with that.

-Hal

 

[GoldDigger]

The only balanced transmission line I have ever seen is 300 ohm twin lead and that was never good at rejecting interference. It had to be twisted to help with that.

-Hal

Actually IBM specified dual core coax (twinax) for data communications for its SNA/SDLC networks, interconnecting terminal equipment with mainframes.
Not sure why IBM made this choice. The touted data rate of 1Megabit/second seems laughably low by current standards. But it was designed for relatively rough usage in uncontrolled noise environments. Since that time coax interconnection technology seems to have progressed in the direction of using better shielding instead of using differential signalling.

In electrical terms, I think an analysis of its characteristics would be dominated by the twisted pair core parameters, with shielding added, rather than a coaxial analysis with exactly balanced currents on core and shield.

 

[ggunn]

Actually IBM specified dual core coax (twinax) for data communications for its SNA/SDLC networks, interconnecting terminal equipment with mainframes.
Not sure why IBM made this choice. The touted data rate of 1Megabit/second seems laughably low by current standards. But it was designed for relatively rough usage in uncontrolled noise environments. Since that time coax interconnection technology seems to have progressed in the direction of using better shielding instead of using differential signalling.

But why not use both? Maybe it's done in audio because the bandwidth is so much lower and 60Hz (the main culprit in audio interference) is in the audible frequency range. 60Hz is virtually DC to video frequencies.

That's complete conjecture on my part, obviously.

 

[GoldDigger]

But why not use both? Maybe it's done in audio because the bandwidth is so much lower and 60Hz (the main culprit in audio interference) is in the audible frequency range. 60Hz is virtually DC to video frequencies.

That's complete conjecture on my part, obviously.

I am reasonably sure that line losses are higher with twinax compared to coax, especially at high RF frequencies.

 

[hbiss]

Thinking about it, our CAT* cables are twisted pair and those handle RF. But you see what's happening there, trying to get more and more bandwidth out of that method is becoming a diminishing return. There is a CAT8 that will go to 2Ghz but it's said to be the end of the line. And with all CAT cables, there are 4 pairs and you are limited to 30 meters.

The thing with coax is that it's cheap and works just fine. No finicky multi-pin connectors, bandwidth up to the point where you would begin using waveguides. Coax can simply be made larger with various dielectric materials and construction methods to cause less loss, and a simple amplifier placed in-line to compensate for it when necessary. Coax is regularly used to go many miles.

-Hal

 

[GoldDigger]

And the connectors needed for twinax are very low volume production, and AFAIK there are none suitable for tool-free or cheap-tool assembly, unlike connectors for coax or CAT.

 

[ggunn]

I am reasonably sure that line losses are higher with twinax compared to coax, especially at high RF frequencies.

With balanced audio cables there is very little signal loss in twinax (is that what you call it?), but the frequencies are virtually DC compared to video, so I dunno. Mic level signal is down around, what, -60dB, and audio snakes are routinely 100' long and sometimes much longer.

Rightly or wrongly, I have always thought that the length restrictions for CATx cable were more about crosstalk between twisted pair signal lines than signal loss.

 

[hbiss]

With balanced audio cables there is very little signal loss in twinax (is that what you call it?), but the frequencies are virtually DC compared to video, so I dunno. Mic level signal is down around, what, -60dB, and audio snakes are routinely 100' long and sometimes much longer.

POTS telephone lines are audio twisted pair and how many miles can that go? :thumbsup:

Rightly or wrongly, I have always thought that the length restrictions for CATx cable were more about crosstalk between twisted pair signal lines than signal loss.

It might very well be, but the bottom line is for data 30 meters is the best current technology can deliver in trying to compete with fiber.

-Hal

 

[BMANN06]

Satellite TV is an ingress only communication system. Your receiver has a one way path of communication from the satellite to your receiver, very similar to your AM/FM radio. Your receiver doesn't transmit to back to the satellite at all. Hence one conductor, and a shielding drain wire/sheath to dump any RFI to ground ... RG6 is definitely the best cable for this application.

 

[LarryFine]

Your receiver doesn't transmit to back to the satellite at all. Hence one conductor, and a shielding drain wire/sheath to dump any RFI to ground ... RG6 is definitely the best cable for this application.

You're not suggesting that coax isn't capable of two-way communication, are you? :blink:

 

[zbang]

Actually IBM specified dual core coax for data communications for its SNA/SDLC networks, interconnecting terminal equipment with mainframes.

Well, not for the mainframes (system370/30x3/etc) which used RG62 (93? ohm), but for the mid-range systems (system3x/as400); nobody liked the stuff and baluns for TP cable appeared quickly. We installed a fair amount of those in the 1980s.

Although.... Direct Attach Copper (DAC) cables for 10G ethernet use twinax as do some other high-speed cables (e.g. SAS3), but it's a wee bit different from that used by mid-range systems.


That said, coax is great for a lot of things, and ground loops aren't as much of a problem for multi-MHz "digital" signals as they are for baseband audio :happyyes:.