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Ground Loop Issue?


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Hi all

 

I have come across this for the first time in my five years of cctv installations.

 

Here is the set up;

 

4 cameras (TVI - from GTec)

TVI DVR from same company

Coaxial Cabling (shotgun)

Cameras powered with a 5A compact (adapter) power supply at the destination (i.e. same place where the DVR is located)

 

Location of DVR and where all the cabling lives; in the loft of a bunglow.

 

Output is completely teary and full of interference; see picture attached.

 

Now I have been in contact with the supplier and they have advised us to carry out few tests and none of them seem to have worked so far:

 

1. At some places our coax cables were first running along the 220V electricals which the company thought  was the major cause of interference. To remedy that we re-routed the wiring, i.e. made sure that it is 'completely' away from the 220s, and the closest we have ever got to a 220v with our cables runs is half a feet. Unfortunately the result is the same level of interference.

 

2. They asked us if by powering up the cameras individually using separate power supplies will fix the issue but using individual power supplies doesn't ever power up the cams.

 

3. We see output on the screen only in the case when ALL FOUR cameras are connected to 1 to 4 way connector lead. if you disconnect one or two from the lead then all the others do not show any video output

 

3.1 Also tried the boxed 10A power supply, same issue persists!

 

4. One of the 4 cameras doesn't even switch on, it comes on briefly for a second and then goes. This cam is the farthest away from the DVR 15 meters i suppose.

 

5. Now this is the reason I think it is a ground loop issue; I can feel a tingle on the BNC connectors at the back of the DVR when i touch them and of high intensity.

 

6. So keeping the above point in mind I decided to order some humblocks from systemQ,

http://www.systemq.com/cgi-bin/commerce.exe?preadd=action&key=CON700

 

connected all of them up but there is NO video output when they are connected :-( The sales guy at systemQ clearly said that these will work with TVI cameras, is there a compatibility issue here?

 

My back up plan is to switch to analogue cameras and then use the humblock with them.

 

Really do not have any other ideas, can anybody suggest anything please? :-(

 

Thanks

Fahad

post-67778-0-09062800-1457995393_thumb.p

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Anything earthed at both ends that shouldn't be? not that there sounds like anything needs to be but sometimes there is.

 

Are you sure when using separate psu's you have the correct rating to power the cameras?

 

A lot of those 5 amp compact psu's are ****!

 

Was the cable of good quality, have you used it before to good results?

Edited by Rob Kirk
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Seems to me you need to remove the DVR, PSU and one camera and test on bench

In point 2 and other places it doesnt make sense , how can you not be able to power one camera ?

Edited by al-yeti
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Adi: Surely reverse polarity won't even power up the cameras? I did notice that one of the connectors was put in with reverse polarity but fixing that still didn't sort the issue out. Does that permanently damage the cameras or the cabling? I will however recheck. And that's what was told to us about humblocks that they will work with TVI.

Sixwheeledbeast: if one of the cameras is not working then when we tried powering up one after the other that problem would have gotten picked up. I will actually try some more combinations.

Rob: yes the supplier did acknowledge that a type of PSU doesn't work well with TVIs so they sent us another one but unfortunately it's the same result. Yes we use that cable all the time and with good results.

Al-yeti: yes I think I need to take it back into lab.

Yes, that's the puzzling part that cameras don't power up with individual power supplies.

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They are not dual voltage.

I think I will check all the power connectors, it could be that one of the connectors has reverse polarity and probably bring the equipment back into to lab for some more testing. If the lab tests are ok then we know its the wiring and definitely a ground loop.

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So to summarise I see the following might the issue and these are the things that can be done:

 

1. One of the cameras may be on reverse polarity

2. It doesn't seem like a ground loop issue, however as I said that I can feel the tingle when I touch the BNC connectors at the back of the DVR.

3. I should bring the equipment back to lab and test it.

4. Most likely to be a power issue, however I have tested with a bigger boxed 10A supply but the same problem persists.

 

Please advise if I am missing some points.

 

Thanks

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It's possible you have a potential on the earth in the building have seen this before , it was resolved by correcting a fault in a socket , however tingling on the bncs maybe a side issue, as those lines or bars or whatever we call them "shouldnt" cause that , maybe it's the power unit, I have seen toroidal transformers cause this in a similar way

As above stick a battery on them and see what happens , if DVR is 12v input then even easier you can stick it all on a battery

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What BNC connectors are you using?

TVI can be very fussy with the BNC termination compared to "old style" analogue.

Make sure when terminating the BNC that the foil shield and braiding on the cable is cut back so its well clear from the centre conductor/pin. You don't normally have to worry about this so much with analogue but I've witnessed a similar fault to what your describing.

Just for test purposes try connecting the camera to the DVR using CAT5 and baluns

Edited by Alpat Systems
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Second above, be extremly careful with the braid and core, happened to me only last weekend!

 

Won't be reserve polarity as it would stop the other 3 from working. That looks like cabling issue, and if you've used that cabling before i'd point my finger at connectors.

 

Have you tried sending a pattern down it? If so what are the results?

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