about ground loops...

[diitto]

I asked this question before but I unfortunately buried it within some other questions so got no responses to this question by itself... So I'll ask it by itself... It's about ground loops... From what I have read and been told the NEC requires the signal cables to have their shields tied to ground outside the structure but at a point as close as possible to the entrance to the structure... OK, so that is ground one which runs from that point back to the main building ground... Then all the way at the other end of the various signal cables, those cables attach to, I assume, a grounded (by third prong of power cord) receiver box, or perhaps to a grounded surge protector box... That ground runs back to the main building ground through the house ground wiring...

Now that creates a ground loop, in fact multiple ground loops for multiple signal wires... Is that an issue??? Am I correct that the receivers are grounded (I am not buying receivers until I get everything else installed so I don't have one to look at today)?? Grounding at multiple locations might improve electrical safety but it usually flies in the face of good signal processing procedures, especially if the ground loops make nice loop antennas!!!

Anyway, so what might anyone be able to share on this topic?? Are your signal shields grounded both outside the structure and at the receivers as well??? Any help would be appreciated... thanks... diitto...

 

[PhillyOTA]

A simplified answer is:

You are not really grounding the satellite, but bonding it to your electrical ground. So they are at the same potential.

Most satellite receivers did not have 3-prongs, I do not know if that has changed recently, but even if they did, it is at the same potential.

I took some liberties to make this concise, but I'm sure someone will point out how I'm wrong.

Eddie

 

[ShadowEKU]

A simplified answer is:

You are not really grounding the satellite, but bonding it to your electrical ground. So they are at the same potential.

Most satellite receivers did not have 3-prongs, I do not know if that has changed recently, but even if they did, it is at the same potential.

I took some liberties to make this concise, but I'm sure someone will point out how I'm wrong.

Eddie

some still dont have the third prong.

But that third prong grounds the contents and the case. the ground block thats outside or very close inside is what grounds the LNB and CABLES... the dish ground is a completely different wire from the dish which can run into the cable ground blocks but can also be bonded to the house ground in addition to the ground blocks.

 

[PhillyOTA]

But that third prong grounds the contents and the case.

and I THINK the shield of the coax connects to the case (chasis), so in this example it may appear as if a double ground/loop problem would occur, which is what I think the original poster was asking about.

Thanks for pointing out about the 3rd prong, I haven't seen any of the current receivers from either provider.

Eddie

 

[ShadowEKU]

and I THINK the shield of the coax connects to the case (chasis), so in this example it may appear as if a double ground/loop problem would occur, which is what I think the original poster was asking about.

Thanks for pointing out about the 3rd prong, I haven't seen any of the current receivers from either provider.

Eddie

Problem wouldnt occur because they are both bound to the same ground... if not then you have an issue.

 

[PhillyOTA]

That's what I said, just trying to pinpoint the original posters confusion.

Eddie

 

[diitto]

...a bit of clarification of my ground loop question seems in order

...But don't think only along the lines of DC or ohmic grounds... That part I think I understand... Instead, think along the lines of a loop antenna... In essence what I described in my original post is a signal wire that is grounded in two locations, one near the "head end", outside near the satellite dish or at least at the entrance to the house and the second at the receiver box connection, assuming the receiver is a case grounded, three prong type chassis... And those two different grounds run back to a single point (the main building ground) via two different wires. If you start from the building ground, run out on one wire to where it attaches to the signal cable shield, say at the one out on the house, then follow that signal cable shield down to the place where the other ground takes off from, say at the grounded receiver case, and then follow that ground wire back through the house wiring to the building ground, you have travelled in a loop, thus the term ground loop... And from antenna theory, any time you create such a loop, any signal in the air (and this would constitute noise to our satellite signal) that has a wavelength comparable to to the loop diameter (in this case many, many meters) will likely couple into the shield if not into the main signal conductor itself... That is how a loop antenna works to first order. And this is what I am asking about... From a safety point of view I have no problem grounding the shield at two locations, thus setting up a ground loop... What I am asking instead is does anyone know whether or not setting up such a ground loop causes them (I am asking for personal experience) problems with the quality of their satellite signals... So the simplest question would be 1) do any of you have your signal shields grounded at two different locations as described above and if so, 2) have you had any problems with the quality of your video signals???

thanks... diitto....

 

[PhillyOTA]

1. Yes

2. No