Ground Loops re re re re Visited AGAIN. (1 Viewer)

[Jeff AW]

Ok, after sifting through a ton a old ground loop posts, none really fit whats going on in my system. So.. I am hoping someone can point me in the right direction..

I have the dreaded cable coax ground loop hum. I have a DIGITAL cable box so most of the isolators DON'T work. They leave weird lines through the first 100 Stations and introduce muck into the digital signal....

Here is the odd part. The house I live in is 5 years old. Properly grounded. Our cable company hooked up the cable ground to one of the copper pipes in the house (not sure which one without looking). The cable hits 2 splits before it gets to me. One for the cable modem and one to split the signal to the other digital box we have. My split runs about 70-80 feet before it gets to me. Once at my living room, I get the dreaded ground loop even though my cable is grounded at the point of entry to the house.

Here is what I did to eleviate about 98% of the hum. I stripped some rg6 off at each end of a spare piece of cable, wrapped the bare copper wire around the digital cable box "Cable IN" connector and stuck the other bare copper into the house ground of one of my outlets. This cut 98% of the hum, but there is still some there, low in volume but still there. The hum increases in volume if I switch it to my VCR (Still running off the same cable)

How can I properly get rid of this ground loop? Not sure if hacking an rg6 cable to house ground is the "right" way to do it... At this point I am up for suggestions.

Thanks

 

[Seth_L]

I have the dreaded cable coax ground loop hum. I have a DIGITAL cable box so most of the isolators DON'T work. They leave weird lines through the first 100 Stations and introduce muck into the digital signal....

Why don't they work? I have Digital cable and I've been able to use one with no problem. I did have to get a cheap cable amplifier from Parts Express, but it works with no hum and I don't have any problems with reception.

Seth

 

[Shawn McBride]

If you unplug you cable from the wall does the remaining 2% of hum go away? I had a cheapo power strip in my system that was causing a hum similar to my cable hum.
My cable hum was an all or nothing signal independant of sources being turned on or off. The power strip induced hum changed depending on what I powered up or down (and where I located the strip!)
BTW, my house is less than two years old, the cable is properly grounded outside, only three outlets in my house and I got cable hum too!
Shawn

 

[Jeff AW]

Seth: The 24 dollar one I bought was supposed to have enough bandwith. When hooked up it created diagonal lines in the forst 100 stations and I would get bad digital skipping. Maybe it was the isolator itself. I was reluctant to put an amplifier on the cable as I thought it might distort the signal even more. With that isolator, I'll have to experiment with the amplifier I have..

Shawn:
When I unplug the cable from the cable box and there is nothing but silence.

Here's what I am thinking of doing...

1. Checking the cable ground, which is grounded to the incoming cold water pipe. Looks clean but I'll remove it off the pipe and take any corosion off then remount. I am HOPING this will solve the problem.

2. Purchasing another isolator ( mine is now DOA ), maybe upgrading to the mondial magic. Maybe a decent power bar. Not sure yet. I am going to experiment first...

 

[Jeffrey Chin]

i witnessed the exact same problem, except i have comcast digital cable. i have it connected to my replaytv as well. save yourself time and headache by buying one of these babies. problem solved.
3 words:
MONDIAL MAGIC BOX
http://www.audioadvisor.com/store/p...20TV%20Isolator

 

[Seth_L]

Save yourself the money and put a cheap parts express 10dB amp before the splitter. I had the exact same problem Jeff had and the amp took care of it.

Seth

 

[Levesque]

I got the exact same problem. All the isolators cannot work with a satelllite antenna because they are interrupting the DC power.

I got an awful hiss coming from my amp when my coaxial feed is hook to my sat decoder. When I unplug this coaxial cable, perfect silence. I plug it, then I can hear the hiss from 10 feet!! I have redone all the grounding of the house, and got a dedicated 20A circuit installed. Everything pass trough a Monster HTS-2500. I have tried to link all the chassis from the pre-amp, amp and sat decoder togethers with copper cables. RF-isolator from Rat Shack doesn't work. 300- 75 75-300 doesn't work to. Nothing works.

I just receive this answer from Jensen about the ground-loop isolators they sell:

"Unfortunately, you cannot use a capacitive (VRD-1FF) or transformer (VR-1FF) type isolator on your satellite cable feed. Both types of isolators will interrupt the DC power to the satellite dish and prevent it from operating. You are going to need to isolate the outputs of your satellite dish receiver box instead. We manufacture isolation units for all of the different outputs that your box might have.
Dale Roche - Project Engineer"... Great...

What are those outouts isolators??

 

[Seth_L]

Radio shack sells RCA cables with isolation transformers on them. So instead of isolating the feed from the dish you isolate the sat decoder from the rest of your system. The problem with this can be that the audio from it is easy to isolate, but the video may not be. I don't know if you can get s-video cables that are isolated.

Seth

 

[Bob McElfresh]

I stripped some rg6 off at each end of a spare piece of cable, wrapped the bare copper wire around the digital cable box "Cable IN" connector and stuck the other bare copper into the house ground of one of my outlets.

OUCH!

You have basically grounded the outer part of the "F" connector to power ground right at the box. But you have bare-copper wire sticking into an AC outlet. This is very bad. What if the wire pulls out, then shoves itself back into ... the hot portion of the outlet?

There is a safer way: hit the hardware/computer store for a inexpensive power strip with "F" connectors as part of it's "Surge Protection". This basically does the same thing: wire the outer part of the "F" connector to power ground. But it's all soldered and much safer.

 

[Wayne A. Pflughaupt]

The house I live in is 5 years old. Properly grounded. Our cable company hooked up the cable ground to one of the copper pipes in the house (not sure which one without looking).

There’s your problem, Jeff. You cable service is not properly grounded. It should be grounded at the same place as the house electrical, i.e., the ground stake (typically near the breaker panel). I’m surprised you didn’t find this out when you did your search on the subject.

Regards,
Wayne A. Pflughaupt

 

[Greg_R]

As Wayne mentioned, your cable is not grounded properly (proper for HT, it's fine for electrical inspection). The easiest method is to get a 75->300ohm and 300->75ohm connector from radio shack. Screw these together and put them into your cable feed. This breaks the ground shield (thus eliminating the hum).

 

[Jeff AW]

An update...


Bob McElfresh:

There’s your problem, Jeff. You cable service is not properly grounded. It should be grounded at the same place as the house electrical, i.e., the ground stake (typically near the breaker panel). I’m surprised you didn’t find this out when you did your search on the subject.

I can't totally agree with you both. (with a little more investigating) The cable ground is actually hooked to the main cold water pipe inlet. It feeds from directly outside about 2 feet to the basement wall. So it may as well be just like a grounding rod in the ground. I'm no electricion but technically they should be the same if not pretty simmilar in effect.

A couple things could blow a hole in my theory, for one. If the copper pipe for cold water is somehow hooked to a "plastic" pipe on the outside, there may not be enough copper on the outside to cause a ground. Heck sometimes its hard to get a good ground even when stuck to earth.

Here is something interesting.... I did a little more experimenting with the rg6 bare copper "widow maker". I have a junction area for my upstairs. In there is a hot water heater, heater, and all my network and cable runs. I hooked the cable up to the fconnector and the COLD water inlet to the heater. Guess what. Hiss was 95% eliminated. However I could still hear SOME hiss but it was faint.
I also hooked up a cheapo Radio shack Cable amplifier to the signal at the junction, still no real difference.

Another twist. When we ran the 220 service upstairs we ran the cable lines near it along with the phone lines. They're not touching the 220 line, but I am begining to wonder about the 220 line introducing 60 hz noise back into the cable AFTER the point of the cable ground, therefore when I ground it again the noise subsides. Any thoughts?

 

[Wayne A. Pflughaupt]

Jeff,

Another twist. When we ran the 220 service upstairs we ran the cable lines near it along with the phone lines. They're not touching the 220 line, but I am begining to wonder about the 220 line introducing 60 hz noise back into the cable AFTER the point of the cable ground, therefore when I ground it again the noise subsides.

Not likely. That’s exactly the reason why RG-6 is shielded.

Regards,
Wayne A. Pflughaupt

 

[Jeff AW]

Wayne....

Thanks for the explaining the double grounding..... I'll be messing with the cable ground tomorrow hooking it up to the actual house ground......

I'll post my results for those that are interested.