Grounding test

[cwdonahue]

Anyone know a test I can use to insure my dish, etc. is properly grounded. Moved a few cables around (removed some diplexers I no longer need) and have a ground hum going in my home theater now. I know how to rule out the wiring in my house. What's a good test to check the cabling from the dish side? If I was a EE major, I'm sure I'd know what to do....

Thanks.

[n3ntj]

I am an EE, but I'd have to see your setup to come up with a remedy. Heck, you could make a little low pass filter using a capacity and see if the hum goes away. Not sure how you can easily test your ground. If you see a proper sized copper line from your dish and ground block connected to your electrical system's ground rod and all of your coax connections are tight, it should be OK.

[cwdonahue]

I'm thinking that when they crimped the connector onto the coax from the dish, they didn't get the shield completely pulled away from the conductor. Visually, I can't see a problem, so I'm trying to remember the best way to test for this. I have a way to determine if my inside wiring is a problem (run a known good cable directly to my satellite receiver to go around the in-wall wiring), but I don't have a simple way of doing this from the dish to my distribution panel in my basement.

By the way, I did sign up for the protection plan a week ago in anticipation of perhaps needing DirecTV to dispatch someone to look at the cables and grounding. Just have to wait it out until it kicks into effect...23 days and counting.

[rkicklighter]

DISCLAIMER: I am not a D* expert but I have been an EE for 30 years and have worked with indusrtial electronics grounding more than I care to remember.

Here's how I would check the cable grounding. First you need access to a Digital Multimeter or an older Volt-Ohm Meter. Using the Ohms setting on either meter, place one lead on the outside of the coax connector, the other lead to house ground. The reading should be close to 0 ohms. Anything over a few hundred ohms and you have the potential for a ground loop. In other words, the cable shield and house grounds are at a different potential or connection to earth ground.

Perform this test ONLY if you know how to use a multimeter properly.

I would also remove power from ALL D* devices, (unplug them). This should not matter but electricity can do weird things.

There are other ways to measure this but they require special meters which can register differences in ground potential to devices from a common ground source.

Hope this helps

[digital223]

I'm thinking that when they crimped the connector onto the coax from the dish, they didn't get the shield completely pulled away from the conductor. Visually, I can't see a problem, so I'm trying to remember the best way to test for this. I have a way to determine if my inside wiring is a problem (run a known good cable directly to my satellite receiver to go around the in-wall wiring), but I don't have a simple way of doing this from the dish to my distribution panel in my basement.

By the way, I did sign up for the protection plan a week ago in anticipation of perhaps needing DirecTV to dispatch someone to look at the cables and grounding. Just have to wait it out until it kicks into effect...23 days and counting.

buy a continuity testing device with a pigtail.
generally a good one has a needle like probe on one end and a pigtail with an alligator clip on the other. they also are available with no probe , but 2 pigtails with alligator clips. it requires batteries. test it by shorting both probe and alligator....the led should light showing the unit is working and the batteries are ok.

you also could use a cheap volt/ohm multimeter.

if it is possible to disconnect the cable in question completely, have an assistant hold the cable so that both connectors are accessible for you to make contact with the pigtail end on one, and the probe on the other connector. the led should light if there is continuity.

you can also check the copper conductor as well.

just remember a continuity tester should never be applied to any live elecrtical circuits !!!!

[n3ntj]

I'm thinking that when they crimped the connector onto the coax from the dish, they didn't get the shield completely pulled away from the conductor. Visually, I can't see a problem, so I'm trying to remember the best way to test for this. I have a way to determine if my inside wiring is a problem (run a known good cable directly to my satellite receiver to go around the in-wall wiring), but I don't have a simple way of doing this from the dish to my distribution panel in my basement.

By the way, I did sign up for the protection plan a week ago in anticipation of perhaps needing DirecTV to dispatch someone to look at the cables and grounding. Just have to wait it out until it kicks into effect...23 days and counting.

Yes, it is very easy to leave a small single strand of coax outer shield short to the inner conductor. I always check this carefully if I have intermittent problems or the connector itself may be loose. You could use a multimeter, but if you're talking about a long distance, it may be tough. Do a continuity check b/w the ground rod and terminal block and see what you get. Should be less than 5~10 ohms. If its a short distance, expect to see 0 ohms.

[cwdonahue]

Thanks everyone. What you are describing is the kind of test I remember from basic circuits way back in my undergrad days. "Us" computer engineers that wanted to work with hardware got thrown in with the EE's going through circuits. I definitely plan to disconnect the cables I'm testing to keep power out of the equation. Not looking to earn the nickname "Sparky" here. The coax termination block is grounded to some electrical conduit that is very close to it, so I don't have a distance problem. The more I look at what's going on the more I suspect the coax installed by the electrician that did the work in my basement theater. I think I have a bad crimp on that connector. Must not like being touched the other day when I took the diplexers out.

[aim2pls]

Anyone know a test I can use to insure my dish, etc. is properly grounded. Moved a few cables around (removed some diplexers I no longer need) and have a ground hum going in my home theater now. I know how to rule out the wiring in my house. What's a good test to check the cabling from the dish side? If I was a EE major, I'm sure I'd know what to do....

Thanks.

ahhhh YES ... the wild and whacky world of ground loops

1) ground loops are caused by a voltage potential between grounds

solution: eliminate the voltage differences

1) tie all the grounds together

2) one by one lift the grounds (NOT the house ground obviously) to find the "bad" one

3) cabling to the dish is typically not the problem .... its grounding can very well be

4) try using a DVM to read voltages between grounds


good luck

[cwdonahue]

ahhhh YES ... the wild and whacky world of ground loops

1) ground loops are caused by a voltage potential between grounds

solution: eliminate the voltage differences

1) tie all the grounds together

2) one by one lift the grounds (NOT the house ground obviously) to find the "bad" one

3) cabling to the dish is typically not the problem .... its grounding can very well be

4) try using a DVM to read voltages between grounds


good luck

Yes, I'm stuck in a loop again here. Tried using the other coax run in my basement...no change. Did a new cut and connector at the grounding block...no change. This is crazy. I have no problems in my family room system. Same dish, same coax, similar A/V system setup (pre/pro with separate amp, DVD player connected via component video to TV, digital optical connection between satellite receiver and pre/pro, coax digital connection between receiver and DVD player, along with 6 analog interconnects for DVD-Audio/SACD from the DVD player).

Time to go back down there and try again.

[SledDog]

Instead of using a Digital VM, I find using analog meter, like a Simpson, works much better. Some times the DVM give inaccurate readings in these types of situations...

[davring]

I would suspect a 60 cycle hum would be picked up between your receiver and your audio amplifier, I doubt it would be on the dish side of your tuner.

[cwdonahue]

FYI

Using a good old analog multi-meter as suggested, I am now satisfied the satellite system is properly grounded. The grounds were a bit sloppy and I improved the situation, but there wasn't enough going on there that would do much harm. Would be nice if the installers actually torqued some screws more completely. Still baffles me why disconnecting the coax from the dish eliminates the hum, though. I only have one item in my whole system that has a three-prong electric plug....my amplifier. Given it's 5x200 watts, it needs a three-prong plug. I'm going to try another test that will take some electrical wiring out of the equation. I'm praying an electrician is not in my future...

Thanks for your help everyone.

[w6fxj]

CW: Go to this web page to read all about the problem you are having and how to fix it: http://www.jensen-transformers.com/ You have a very common problem that can be cured.

[Stevies3]

I had this issue with my HT application & must tell you it drove met nuts. The humm was so annoying althougH it was very low. The fix was a simple device you can purchase at any Radio Shack. (link enclosed) You may need a few depending on how many devises are in your system.

http://www.radioshack.com/product/index.jsp?productId=2062214&cp=&sr=1&origkw=ground+loop&kw=ground+loop&parentPage=search

[n3ntj]

I would suspect a 60 cycle hum would be picked up between your receiver and your audio amplifier, I doubt it would be on the dish side of your tuner.

Heck, if its AC hum, you can build a simple low-pass filter.

[BKC]

The home theater wouldn't by chance be a Onkyo HT-R340 would it?

[cwdonahue]

CW: Go to this web page to read all about the problem you are having and how to fix it: http://www.jensen-transformers.com/ You have a very common problem that can be cured.

I assume you are pointing me at ... VRD-1FF Cable TV Ground Loop Isolator
Analog, Digital and Cable Modem Compatible ... which is on the page. Anyone tried one of these with the DirecTV system? I've looked at this in the past and wasn't sure if it worked. Wasn't about to cough up $60 on a crap shoot.

[cwdonahue]

I had this issue with my HT application & must tell you it drove met nuts. The humm was so annoying althougH it was very low. The fix was a simple device you can purchase at any Radio Shack. (link enclosed) You may need a few depending on how many devises are in your system.

http://www.radioshack.com/product/index.jsp?productId=2062214&cp=&sr=1&origkw=ground+loop&kw=ground+loop&parentPage=search

Thanks for the suggestion, but don't think this applies. The ground loop appears through the satellite coax connection. I don't even have any L/R simple audio connections in my system.

[cwdonahue]

The home theater wouldn't by chance be a Onkyo HT-R340 would it?

Sounds like a leading question there, but no.

I have a Rotel RSP-1068 Pre/pro and an Outlaw Audio 770 amplifier (5x200W per chan). Yes, I like to rock the house!

[cwdonahue]

I found that if I use extension cords to connect my amplifier to the 120V outlet at my electrical panel, the hum is gone. The electrical system in my basement was "added on" when it was finished several years after my house was built. I guess the satellite is grounded to the "original" house wiring and the basement ground doesn't seem to be common with the original wiring? Weird given both use the same breaker panel. Any of this make sense to folks that understand residential electrical wiring better than I do? Perhaps the electrical boxes aren't grounded properly that were added? If my wiring is a bit suspect, I guess the best solution is to get an electrician....

[BKC]

Sounds like a leading question there, but no.

I have a Rotel RSP-1068 Pre/pro and an Outlaw Audio 770 amplifier (5x200W per chan). Yes, I like to rock the house!

LOL No it's just that model had a problem where the speaker wires were hooked to the unit that caused a hum in the sound.

[cwdonahue]

I thought I'd post how I fixed my grounding problem just in case this helps someone else in the future....

I went back to "square one" which is determining where the grounding difference causing the hum is getting into my audio system. So, I started pulling cables that connect the TV to the system. I can rule out the Xbox360 as a source. It may be connected to the TV via component video cables, but it is connected to the pre/pro via a fiber optical cable. There are two video connections that provide a metallic path to the pre/pro....component video cables from DVD player to the TV (there is a metalic path from the DVD to the pre/pro via 5.1 analog outputs), composite video connection from the pre/pro to the TV to view its setup menus. I pulled the component video cables from the DVD player and the composite cable and things got quiet. So, the path of the hum is from the video connections of the TV. This is what I had previously discovered.

Another source of difference that can be ruled out is plugging devices into different circuits. The pre/pro, DVD player, HR21, and HDTV are all plugged into one Richard Gray's Power Company 400S to insure they are all connected to the same ground and surge protected. The 400S is overkill, I know.

If it's coming into the system via the outputs of the TV, then the input to the TV must be where the ground difference is coming from. So, I'm right back to the satellite system where I started. I pulled the HDMI connection from the HR21 to the TV along with the pair of analog audio cables (TV has a DVI input, so audio comes through separate pair of cables) and the hum stopped. This is the same effect as disconnecting the coax to the receiver at the grounding block from the dish.

I finally realize I haven't tried grounding the satellite coax to the ultimate ground in any house....the cold water inlet pipe to the hot water heater. The cold water pipe comes in underground, so it's really grounded. At one point I thought my OTA was part of the problem, so I had grounded it to the cold water pipe. Things improved some, but it clearly wasn't the ultimate solution.

So, I pulled out some 12 gauge wire I had on hand and ran it from a grounding clamp on the cold water inlet pipe to the grounding block for the satellite coax. Bingo! No more hum. I proceed to kick myself in the rear for not figuring this out long ago when I first went down this path.

I'm still not sure why this is the solution. Each pair of coax from the dish is terminated on a separate grounding block that accepts two coax connections. The pair of coax connections on one block attach to satellite receivers that are plugged into the original house wiring. The second grounding block has one coax going to my family room HR20 which is also connected to the original house wiring, while the second coax goes to the basement home theater that was added on to the electrical system when the basement was finished. Somehow, a common ground must not be there between the two systems. I've never ever had a ground hum in my family room system. Oh well, no hum. Now I can go back to listening to clean audio.

[JeffBowser]

Excellent, thanks for that terrific summary on the solution !

[cwdonahue]

CW: Go to this web page to read all about the problem you are having and how to fix it: http://www.jensen-transformers.com/ You have a very common problem that can be cured.

Forgot to add that I did check out the Jensen stuff along the way here.
They don't have a product that is compatible with satellite systems, since satellite receivers push power up the coax to the dish. If I tried to put isolators at the HR21, well, they only have an isolator for my L/R audio connections. They have nothing for HDMI. In the end, I probably could have used their stuff, but I'd need isolators on the component video connection from the DVD player, the composite video connection from the pre/pro, etc. It would add up fast. A grounding clamp and a piece of 12 gauge wire is a lot cheaper! It's just figuring it out, that's the challenge.

[K4SMX]

Wasn't there a thread around here somewhere, "To Ground or Not to Ground?"...."Grounding, Yes or No?"......something like that? I exercised restraint. :) :)

Here it is: Another Grounding Question (http://www.dbstalk.com/showthread.php?t=117336)

[Annihilator31]

Here's a suggestion, "Remove the ground" it's useless anyway! Go buy a good surge protector.