Ground Loop Isolators - Cure Or Cover Up?

[sjsturner]

Hes refering to having cheap balun rack. You need decent stuff when dealing in said situation. Swopping a cheapo rack with another cheapo rack wouldent prove anything. What concerns me is the fact that you powered them on batt and still got probs, in my experience when earth loop is the culprit and you eliminate it using batt the pics should clear up.

All of this is assumption tho and would like to be clear your not being accused of using cheap **** its just cheap balun and psu play a big part in these types of issue.

I would do as 6wb and see what you find.

When the other side cams are all disconnected from rack power them on their local supply and plug one into a batt powered test monitor and see what its like. Then plug into your dvr and check the difference.

Sounds like you have more than just earth loops going on imo

Good luck

[timmo66]

It may be a fact of cheaper equipment. We haven't used these make of baluns and racks before.

This is driving me mental. I can usually switch off after hours but not this time for some reason.

Is it possible that I am not getting the earth inbalance from the power, but perhaps down the pair due to a cheaper balun at the camera? The inbalance comes when it hits the metal balun rack. But then surely that problem would be resolved when I took the rack off the patch cabinet?

First thing Tuesday morning I am going to put a genie balun at the camera, a genie balun at the DVR, and see what happens.

http://www.dynamic-cctv.com/shop/CAT_5_Transmission.html these are the baluns and racks we are using (passive)

[sixwheeledbeast]

Hes refering to having cheap balun rack. You need decent stuff when dealing in said situation. Swopping a cheapo rack with another cheapo rack wouldent prove anything. What concerns me is the fact that you powered them on batt and still got probs, in my experience when earth loop is the culprit and you eliminate it using batt the pics should clear up.

All of this is assumption tho and would like to be clear your not being accused of using cheap **** its just cheap balun and psu play a big part in these types of issue.

I would do as 6wb and see what you find.

When the other side cams are all disconnected from rack power them on their local supply and plug one into a batt powered test monitor and see what its like. Then plug into your dvr and check the difference.

Sounds like you have more than just earth loops going on imo

Exactly. Batteries are a very good tool for ruling out a mains issue.

 

Sorry, but could you elaborate on your first point?

A ground loop is when "x" and "y" is connected together that are suppose to be at a common potential but actually have different potentials to ground.

This can happen when two active devices are powered locally and there is unwanted current (difference in potential) flowing between them. This form of ground loop that presents itself as 50Hz humming or harmonics thereof; is known as a "mains hum".

Phase shift is when two active devices are powered locally on different mains phases.

While my AC theory isn't as good as my electronics, I can explain that in CCTV systems it causes a rolling and sometimes fuzzy, ghosting effect.

Also don't rule out good old fashioned interference, RFI and EMI.

Whenever possible star grounding should be used on audio/video signals, this means all earths are tied to the same potential.

We are powering the cameras with various power supplies at the camera locations, all of which are actually different makes and types. For example we have a 4 way 5amp power supply fitted at one corner of the building, we have two moulded power supplies inside a column at another corner, and a 24v AC power supply feeding the dome at another corner.

Maybe one of your powers supplies is poor quality or faulty. Moulded switched mode power supplies are generally unclean and noisy, without very good filtering.

I haven't actually tried a loop isolator yet no. I have plugged a hum eliminator on but this only clears the fault on a camera when a single balun is fitted at the DVR instead of the balun rack.

Well I wouldn't go buying 21 yet.

I have a "humbar" in the van purely for diagnostic purposes.

Do remember passive baluns are a form of ground isolation, so I doubt this will do anything but kill the gain of the signal.

[whistle]

I once had a moulded power supply in a roof space of a school causing problems on at least 10 cameras on site. We had rolling bars and ghosting across most of the cameras on that DVR. Once we replaced the £8.00 PSU the problems cleared up.

[timmo66]

Yes i have had problems with moulded power units before, changed the two i have fitted on site but still no change.

I have plugged one camera in at a time with all other cameras disconnected, so it doesnt look like its one particular camera or psu causing the problem.

[sjsturner]

Yes i have had problems with moulded power units before, changed the two i have fitted on site but still no change.

I have plugged one camera in at a time with all other cameras disconnected, so it doesnt look like its one particular camera or psu causing the problem.

Plugged one in where? Single balun in dvr?

Or your rack?

[timmo66]

Plugged one in where? Single balun in dvr?Or your rack?

I had to think about this because i tried so many things on thursday.

I meant directly into the dvr via a single balun and hum eliminator. I cant get a clear picture through the rack on the cameras from across the way, even with the hum eliminator.

[sjsturner]

I had to think about this because i tried so many things on thursday.

I meant directly into the dvr via a single balun and hum eliminator. I cant get a clear picture through the rack on the cameras from across the way, even with the hum eliminator.

How About at dvr end plugged into a test monitor?

Do you have access to a ups?

[timmo66]

How About at dvr end plugged into a test monitor?

Do you have access to a ups?

Plugged into a test monitor at DVR end still produces the same picture (via the rack)

Yes they will no doubt have a UPS on site that i could try. Worth an attempt you reckon?

[sjsturner]

I think so.power dvr off ups and then connect far cams to dvr. The ups will drop earth so you wont have ground loop problem. Or... Use extension lead and power dvr from the supply in tha far building just to see what its like