LNB cable and voltage question

[rowdymon]

Why does RG5/RG59 cable cause a problem with heat on my DirecTivo while the RG6 does not? I recently had a overheated Tivo and I was told it was probably due to the RG5 cable coming in. Can somebody shed some light on this?

THX

RD

[Wedgecon]

The only way I could think the cable could cause the Tivo to overheat would be due to the resistance of the cable being different. But to be honest I thought the only thing that using RG59 would do is give a weaker signal at long distance.

[rowdymon]

And does RG5 cable cause something to overheat ?

[Bud]

The cable carries voltage from the receiver to the LNB on the dish. RG-6 cable is recommended. If the smaller/cheaper RG-59 is used, it is possible the receiver has to work harder to supply the proper voltage to the LNB. Cable is cheap. Replace it before you mess up your Tivo!

[rowdymon]

I'll replace it. Does it matter what kind of cable I have going from the LNB to the switch too?

[Jacob S]

Yes, it matters what type you use for that as well. Anything that goes between the dish and receiver should use RG-6 cable.

[rowdymon]

OK, thx a lot. One more thing; some of the RG6 have a little extra copper wire that piggy-backs on top of it, and some don't. Does it matter if the wire I buy has this or not?

[boba]

That cable is called a messenger and is normally used to ground the system. Unless you need to ground your system it will just cost extra.

[Nick]

"Unless you need to ground your system it will just cost extra."

Grounding is NOT optional.

[AntAltMike]

The little wire is 17 gauge copper clad steel ground wire that actually meets the model electrical code for grounding a mast, but not for grounding a coax outer conductor. The mast can be grounded with 8 gauge aluminum, 10 gauge copper or 17 gauge copper clad steel, solid or stranded, insulated or bare, and connected to your building's ground electrode.

I have never heard of RG 5 coax. RG59 has higher resistance per foot, which means that less current will run through it, which would ordinarily make your receiver run imperceptibly cooler. Too long a run of RG59 (like 300 feet) can result in your system being unable to develop 18 volts at the LNB, which means that you will lose access to the even transponders, and can weaken your signal to below your receiver's input threshold.

Old RG59 coax is more likely to have copper braid shielding, so a poorly installed F connector may more likely short the center conductor to the shield, which will result in overheating or worse.

[Mike500]

I'd go with 90% or quad shielding for better conductivity. Also, there are new 2.2 to 3 Ghz certified grounding blocks and barrel connectors that have much more surface contact area. They are plated silver and have blue insulators. It takes more force to insert the center wire into this type of connector, and from my experience, you have to wrench the nut down from the first thread engagement. Better contact means less resistance.

[rowdymon]

I still don't understand why using a RG5 cable would cause my tivo to overheat. It's getting less power due to more resistance, isn't it?

[Mike500]

Originally posted by rowdymon
I still don't understand why using a RG5 cable would cause my tivo to overheat. It's getting less power due to more resistance, isn't it?

The power supply of the tivo unit has to drive the lnb. The resistance in the RG59 causes heat build-up in the entire system, since the whole systems compensates for this resistance.

[Jacob S]

How long of a wire run with RG-6 Dish Network wire can you run before there is a heat build-up and/or the receiver will not function properly?

[Mike500]

It depends on the resistance of the cable. The center conductor, if copper, will have less resistance than copper clad steel, commonly called "copperweld." The other component is the cable's shielding, which is the return leg of the circuit. 60% shielding has more resistance than 90% shielding. Quad shielding has less resistance that regular shielding. A high end cable, like Monster Cable, has both a solid copper center conductor and copper shield wires, although the foil is vacuum deposited copper on mylar, It is however noted that a center conductor made of copper is more easily damaged that a copperweld conductor. That is the reason why almost all direct burial and aerial drop cable has copperweld center conductors. Solid copper is also subject to tension elongation much worse than copperweld. This is equivalent to tension drawing of the wire. It causes the wire to be reduced in gauge diameter, which causes more resistance. The best outdoor cable is probably "flooded" with an anti-corrosive agent. Corrosion of the shield degrades conductivity. One way to tell is the UL Class "CL" rating of the cable. If UL listed, most cable is rated CL-2. Cables with less resistance is rated CL-3, Basically, because of less resistance it can handle higher voltages. With DBS Lnb's the ability to handle higher voltages in immaterial. It is however noted that the higher UL rated CL-3 is a more durable cable that has less resistance, since the ability to handle higher voltages is directly related with a heavier duty cable with less resistance. So, a CL-3 rated cable is what you will be looking for, if you are running a long distance. Times Fiber Lifetime is a good cable for a long run, because it has a 95% shield, and it is lightly "flooded" to resist corrosion. The highest quality RG-6 for a long run would be UL CL-3 rated Monster cable, where all metal conductors are solid copper.

[Karl Foster]

I have a semi-related question:

I have a 2X6 multi-switch with all six outputs used to four different receivers. How does the LNB receive power through a multi-switch? Does it alternate between receivers, or is it all captured in the multi-switched and then passed to the LNB?

Just curious.

[apc1]

Karl, if your multi switch has it's own plug in power supply, the switch powers the lnb and the ports are voltage blocked. If it does not have a seperate power supply, it is referred to as passive and uses the voltage from the receivers to power the lnb.
Hope this helps.

[DoyleS]

So far there has not been a reasonable explanation as to how RG59 cable could cause the receiver to overheat. Heat is generated by heavy current flow. A higher resistance cable causes less current to flow. A shorted cable causes more current to flow and could cause overheating. RG6 is recommended for all runs on Satellite gear with the possible exception of extremely long runs where one might consider RG11 or a booster amp. The problem with RG59 is signal loss. On a short run even good RG59 would work but RG6 is still recommended. If the loss in a cable is too great it is possible that the LNB signaling voltages won't be high enough to switch from odd to even channels. This would show up as faulty channel switching but still should not cause a receiver to overheat.

..Doyle

[rowdymon]

My theory is that due to more resistance, the receiver needs to exert more power in order for its signals to reach there and back. Of course that would mean that the receiver is monitoring voltage strength and dynamically altering that strength. I don't know if that's the case.

[AntAltMike]

Originally posted by rowdymon
My theory is that due to more resistance, the receiver needs to exert more power in order for its signals to reach there and back. Of course that would mean that the receiver is monitoring voltage strength and dynamically altering that strength. I don't know if that's the case.

Actually, it would have to be monitoring and regulating current output, not voltage, to respond in a manner that would compensate for excessive cable loss and generate more heat, but I'm sure that is not the case. I'm still betting on a single strand short between the outer and center conductors.

The other possibility is that overheating is slightly more likely when both tuners are tuned to even transponders, since the receiver is putting out nearly 50% more current when sourcing 18 volts to call for even transponders.

RG-59 is almost never a problem in DBS installations. I have often sent signal down 300' of RG-59 with no performance problems.

[rowdymon]

So is it fair to say that an RG59 run of about 75 ft would be acceptable for Dishnetwork receivers? I obviously won't use that run for my Tivo but I might use it for a future receiver (if i decide to get a 721 for example). I'm going to add another RG6 run for my Dtivo, but I don't want to get rid of this run.

[Jacob S]

It depends on the quality of RG-59. I had some people that had RG-59 in their installation where it wuld not work.

[apc1]

Rowdymon, as a professional, I cannot condone the use of RG-59. Not saying that it won't work, it may on a short run. If you're going to add an extra RG-6 to the Tivo, why not replace the 59? Just a suggestion. If you are totally set on keeping the 59, take one of your receivers and hook it up to that drop. Check signal strength and let it run awhile and see what happens. Though the proper thing to do is replace the line.

[rowdymon]

I think I might just keep it up there and test it out with one of my 2700 receivers. If it keeps working, good; if not, then all I lose is a crappy receiver.