Need help diagnosing camera power/picture quality problem

[spixel]

I have a camera which is connected to a dvr approx 75metres away. Its being powered locally as there is too much voltage drop with the power attached to the coax.

Some power supplies will result in a picture but there is obvious interference/image ghosting/horizontal lines/moving waviness. The interference never moves up or down the picture, it just stays in the same place. Some power supplies will give no signal at all, some will give a signal but only if plugged into a certain outlet. All the outlets work fine when they're powering cameras that are connected locally. The camera is receiving power in all cases as the IR lights come on. All the power supplies work fine when powering other cameras.

The coax is run underground beside a powerline connecting both areas however I've turned off the power and the problem is exactly the same.

I've replaced the bncs on both ends, no difference. The cable is solid copper core with copper braiding but no foil.

The problem is not the camera as I've tried others. Its either the cable, grounding issue etc. Any ideas what I could try? Replacing the cable is not possible due to how its fitted

 

[alastairstevenson]

Guessing a bit here ...

Some power supplies will result in a picture but there is obvious interference/image ghosting/horizontal lines/moving waviness.

If you are getting variable results from different power supplies which are nominally equivalent, it may suggest a ground loop problem.

The coax is run underground beside a powerline connecting both areas however I've turned off the power and the problem is exactly the same.

Presumably that still leaves a power source in the location of the camera, which therefore might point to that as the cause..
What you've described sounds like a ground loop problem as opposed to a fault with the cable.
Are the power supplies feed from a 3-pin source including ground? If so - can you temporarily isolate the ground?

For similar symptoms caused by ground loops there are 'ground loop filters' that break the solid connection that connects the mains frequency component between the 2 ends but leaves the video signal.

 

[spixel]

Guessing a bit here ...

If you are getting variable results from different power supplies which are nominally equivalent, it may suggest a ground loop problem.

Presumably that still leaves a power source in the location of the camera, which therefore might point to that as the cause..
What you've described sounds like a ground loop problem as opposed to a fault with the cable.
Are the power supplies feed from a 3-pin source including ground? If so - can you temporarily isolate the ground?

For similar symptoms caused by ground loops there are 'ground loop filters' that break the solid connection that connects the mains frequency component between the 2 ends but leaves the video signal.

I did the test shown here How Do I Identify a Ground Loop? | OpenEye and was given a reading of -.09 with volt meter set to 20ac. The reading is 0.4 when set to 200dc

When I test the cable of a working camera the reading is .2 ac and .1 dc

 

[alastairstevenson]

a reading of .09 with volt meter set to 20, 90 when set to 200. I assume .09 is the correct reading

The suggests to me that the camera end of the cable is floating - ie not grounded.
If 0.09 is a true reading, it's a fair proportion of the typical 1V video signal level.

As an experiment, with the camera and DVR powered as normal, can you run a temporary ground to the outer of the BNC connector at the camera end, and see if that makes any difference?

 

[spixel]

The suggests to me that the camera end of the cable is floating - ie not grounded.
If 0.09 is a true reading, it's a fair proportion of the typical 1V video signal level.

As an experiment, with the camera and DVR powered as normal, can you run a temporary ground to the outer of the BNC connector at the camera end, and see if that makes any difference?

The reading is minus .09, whereas its plus .2 on a working cameras connector, does that change your opinion or did you just forget the - in your reply

 

[alastairstevenson]

The reading is minus .09, whereas its plus .2 on a working cameras connector

That sounds like you are measuring DC Volts, not AC Volts, which is what a ground loop would consist of.
You are measuring the outside of the connector relative to the case?

Did you try the grounding test at the camera end BNC connector?

 

[spixel]

That sounds like you are measuring DC Volts, not AC Volts, which is what a ground loop would consist of.
You are measuring the outside of the connector relative to the case?

Did you try the grounding test at the camera end BNC connector?

It's minus .09 with AC, 100% certain. And when I tested the other cameras connector, made sure to not reverse the probes. Do you think the fact the non working camera is showing minus whilst the working one is showing positive is a sign of anything? I done it the same way as shown in that website, outside of connector to unpainted screw of dvr casing. Not tested at camera end yet.

 

[alastairstevenson]

It's minus .09 with AC, 100% certain.

Well, that's weird. An AC measurement doesn't usually give a polarity.
Your multimeter has both an AC volts and DC volts selection - or is it an auto-detect selection?

Do you think the fact the non working camera is showing minus whilst the working one is showing positive is a sign of anything?

Hard to know, to be honest.