Problem With Video Over Cat5e Using Baluns

[Djbesman]

Good day all. I hope someone can shed some light on this for me. I have a client who has done CCTV installation where they have installed ove 64 cameras. They are using Cat5e for all the cable runs and in some cases have 4 cameras running on one length of cat5e cable ( thats using 1 twisted pair per camera.) Now the problem they are having is that on a certain run where they have 4 cameras on the cat5e, 3 of the cameras out of the four were distorting, as if power interference. I.ve sent him cat5 ground loop isolators and this has somewhat cleared up the picture although he stilll has 5% of the top of each picture distorting. Strangely thouh this only happens when he plugs the cameras into the PC Based DVR but when pluged into a standard CRT/ CCTV monitor the picture is clear even with out the ground loop isolators. They'vetried re running new cable, changing the powers supplies and swopping the cameras around, but just on this cable run they have thsi problem of the distorted picture. What can be the problem and how can it be resolved. Any assistance will be very much appreciated.

Thank you....

[arfur mo]

Good day all. I hope someone can shed some light on this for me. I have a client who has done CCTV installation where they have installed ove 64 cameras. They are using Cat5e for all the cable runs and in some cases have 4 cameras running on one length of cat5e cable ( thats using 1 twisted pair per camera.) Now the problem they are having is that on a certain run where they have 4 cameras on the cat5e, 3 of the cameras out of the four were distorting, as if power interference. I.ve sent him cat5 ground loop isolators and this has somewhat cleared up the picture although he stilll has 5% of the top of each picture distorting. Strangely thouh this only happens when he plugs the cameras into the PC Based DVR but when pluged into a standard CRT/ CCTV monitor the picture is clear even with out the ground loop isolators. They'vetried re running new cable, changing the powers supplies and swopping the cameras around, but just on this cable run they have thsi problem of the distorted picture. What can be the problem and how can it be resolved. Any assistance will be very much appreciated.

Thank you....

the 'clue' is in that it works ok to the crt, had you not mentioned it already, would have advised to try that test 1st.

dvr's are far more 'fussy' about the signal stregnth and quality received than a crt, being digital the 'flyback' syncing is more critical, a weak signal often upsets the time base when stronger signals are available on other inputs and displaye at the same time.

so my guess is you will need active baluns on the affected camera's, choose ones with variable video gain adjustment, or fitting an adjustable video amp at the dvr end might fix it, and worth a try if you have one to hand.

regs

alan

[Djbesman]

the 'clue' is in that it works ok to the crt, had you not mentioned it already, would have advised to try that test 1st.

dvr's are far more 'fussy' about the signal stregnth and quality received than a crt, being digital the 'flyback' syncing is more critical, a weak signal often upsets the time base when stronger signals are available on other inputs and displaye at the same time.

so my guess is you will need active baluns on the affected camera's, choose ones with variable video gain adjustment, or fitting an adjustable video amp at the dvr end might fix it, and worth a try if you have one to hand.

regs

alan

Thank you Alan will give that a shot...........

[nikko]

Greetings.

What type of camera are they?

If the picture appears ok on a straight forward monitor but not the dvr, then this tends to be due to poor sync or video levels from the cameras composite video output. Such levels are more critical to devices which "process" composite video such as dvr's but can be tolerated by simple devices such as your monitor.

A composite video signal should comprise of 1vPP and 0.3vSYNC and a chromaburst level. I've known of 0.27vSYNC to cause tearing on the screen when going through processing, it can be that critical!

The best way of checking levels is by an oscilloscope terminated to 75 Ohms, alternativley use a handy level meter,CLICK HERE.

Secondly, try the camera by setting it up next to the dvr. If the problem goes away then distance is probably the issue, if it remains then the camera is the issue.

If the problem is distance then you can try fitting lauch amplifiers. If the problem is the camera, try swapping it for a known good one to see if the problem clears. If so, you have a dodgy camera which needs replacing.

[Ard Disk]

We had a similar problem at a site where we later found there was a serious mains earth fault-

there was no earth, it had corroded. (

We had problems with picture rolling and distorting (partly solved with isolators).

Good earth stakes on the mains supply in each building solved the problem for good.

[Djbesman]

We had a similar problem at a site where we later found there was a serious mains earth fault-

there was no earth, it had corroded. (

We had problems with picture rolling and distorting (partly solved with isolators).

Good earth stakes on the mains supply in each building solved the problem for good.

Thanks Ard, also sounds plausible. Will contact my client to have all the mains electrical plugs rechecked.

[Ard Disk]

Thanks Ard, also sounds plausible. Will contact my client to have all the mains electrical plugs rechecked.

Our "problem" ended up a year later with a cooker fault to the earth in the commercial kitchen, earthing through the best line of earth it could get....

our camera tower! Buried 1m in the earth, it became the focus of a 240v cookers lust down the 3pin plug of the monitor. Then it went to the earth sleeve of the coax to the DVR, then to the cat5, to the cameras, which where firmly bolted to the tower.

It melted all the cat5e, the baluns, the cameras were all shot once the baluns melted and applied 240v to the BNC output, the DVR case was humming even though it ran on 12v psu.

Only the monitor survived. The tower was undamaged.

Thank the lord for the client's insurance:-)

[sjonley]

Hi

Is the guy doing the install a CCTV installer? If not there a couple of questions that need answering firstly.

What type of distortion is occuring. describe it?

1. Is the cable a true CAT5 and not just a twisted pair. Does the spec say CAT5?

2. Are the problem cameras using passive or active baluns?

3. Are the baluns single or part of a hub?

4. How long are the cable runs for the cameras showing distortion?

5. Are there any "kinks" or very sharp bends in the cable run that may cause breakage?

6. Do the baluns terminate at the same point or are you trying to "breakout" at different points on the cable run?

Possible Solutions?

1. If the cable is not a true CAT5 specification, such as BT twisted pair, the "twists per inch" may not occur at the correct spacing.

2. With a passive balun the total distance including coax should not exceed 300m for a colour camera. If the cable run on CAT5 is up at the 300m mark and additional coax is then added both ends, lack of video content may occur.

When using active baluns, past experience has shown that when they are powered, if the distance is under 300m the signal can be overdriven and no adjustment to turn a bright image down is possible. A mixture of passive and active may be possible but consult the balun supplier/manufacturer.

Also with active baluns, only use one twisted pair, per CAT5. if more than one pair is used within the same CAT5, near and far end crosstalk can occur distorting images. Running four CAT5's next to each other (1 pair, per video signal) has enough spacing to stop near and far end crosstalk.

3. Have the Baluns been checked on a short length of CAT5 to test signal integrity?

The reason that when the signal is plugged into a monitor the image seems fine, is that the monitor is less tolerant to the 1v p-p signal than the pc dvr may be. If there is a slight dc offset on the camera signal, the pc dvr will be seeing more black level than the full 0.7v signal range, but the monitor may be tollerant upto 2v, hence a clear image.

[SystemQ]

the 'clue' is in that it works ok to the crt, had you not mentioned it already, would have advised to try that test 1st.

dvr's are far more 'fussy' about the signal stregnth and quality received than a crt, being digital the 'flyback' syncing is more critical, a weak signal often upsets the time base when stronger signals are available on other inputs and displaye at the same time.

so my guess is you will need active baluns on the affected camera's, choose ones with variable video gain adjustment, or fitting an adjustable video amp at the dvr end might fix it, and worth a try if you have one to hand.

regs

alan

That

[justin]

Also with active baluns, only use one twisted pair, per CAT5. if more than one pair is used within the same CAT5, near and far end crosstalk can occur distorting images. Running four CAT5's next to each other (1 pair, per video signal) has enough spacing to stop near and far end crosstalk.

Has anyone else had any problems sending multiple signals with active baluns down the same CAT5 cable. I have used passive ones before and not had a problem.

I have a site where I need to get 2 cameras on each of the 4 corners of a large building. I was looking at running one external grade CAT5 cable to each corner, installing two baluns in a 4x4 external box for the video connections.

I would also like to trust my RS485 data to go down the 3rd pair of the same cable for telemetry.

For the 4th and final pair I would like to send a normally closed alarm input back from a redwall or door contact etc to the DVR.

One cable would make life so much easier for this one.

If the distances turn out to be too far for the passive baluns and I need to fit an active one is this best at the camera or DVR end?

I can mix these can't I?

As I am led to believe, if the distance is not far enough two active baluns could cause a too strong signal.

Thanks in advance.