CCTV Installation Problems

[tmm]

Dear All,
I have problems with an installation consisting of 8 PT, 7 PTZ cameras and 16 dome cameras. All connections from the cameras are via CAT5 with baluns on both sides. Some cameras have local power supplies and the others are powered from a 12v (5amp 12v dc with 9 outputs) and 24v (6amp 24v ac with 6 outputs) power supply unit. The distance from the power unit to the various cameras vary from 2m to approx 50m. I am using 2 DVRs to terminate all the cameras. The problem is that all the cameras connected to the power supply unit have a Hum bar (which i read from this forum is due to earth looping). Also when only one of the cameras powered from the power supply is plugged into the DVR, the picture is fine, if another camera powered from the same power supply is plugged into the dvr, the bar appears on both displays. Any help would be much appreciated.

[Drift]

What balluns are you using? Cheap balluns can actually cause similar effects to ground loop issues. Before you go spending a fortune on decent ground loop isolators, try a pair of different balluns on a couple of the cameras and see if that solves the issue.

[FordTech]

One problem you may have is having ptz's connected to a common power supply, I have seen people running ptz's ac or dc of a common supply and it causes lines through the screen and the lines get worse when you move the ptz becuase of the more current being drawn. Have you measured the current being drawn by your dc cameras, do the cameras have ir?, remember when the ir kicks in the camera will draw more current, is the power supply big enough?. What is the voltage comming out of the power supply?, you might be supplying to much voltage at the camera. A 12vdc ir camera may not like 13+ vdc at it. One thing I have seen is people use 2 pairs of wire at a ballun ie green pair + of ballun and blue pair - of balun rather than a pair of wires for the ballun ie green + and green/white -. I would leave the ptz's disconnected if of a common supply and start of by only connecting fixed cameras that are powered from the same power point at the dvr. If that works ok then look at connecting other cameras one by one. If the site has 3 phase power then, the cameras you have powered locally may be on a different phase to the dvr and that can cause lines through the picture requiring a hum bug. As Drift said it may be your balluns and another thing you should have is a good battery operated cctv test monitor to check cameras individually.

[Drift]

There's a trap for young players with test monitors in that you'll get a perfect image regardless of ground loop issues on site, as there's no common ground. Just something to be mindful of lest you start thinking you're going nuts on site.

Also, just a minor niggle on FTs comment about voltage. Most, 12v cameras are quite happy to operate on between 11.5 & 14v without kicking up a stink. You'll only really start to see issues with voltages outside of these parameters.

Oh another thing just popped into my somewhat hungover head. The 12v PSUs you're using. If they're switch mode or cheaper regulated units, chuck a cro across the output and check for ripple under load. I've seen some shocking units lately that would almost pass as AC supplies. Yet another thing that can cause similar effects to ground loop.

[Privatteer]

Try disconnecting the cameras you have the remote power supplies on and test the cameras on the local power supply only.
Never had an issue with having multiple PTZ's on a decent quality power supply.

[tmm]

Wow,replies much better than i expected, will be checking out all the advise and giving feedback . Thanks a bunch, help me solve this one and i owe you all one.