Extreme interference with active baluns

[koolmer 0]

Hi All,

 

I have a problem at a Warehouse. The screen is about 300 meters away from the DVR. First I used passive GE baluns. There was some noise and interference, but it was not horrible. I then got an active receiver, which made the picture clearer - not perfect.

 

After a few weeks I noticed that the picture had a lot of interference. I have not changed anything, but there was so much interference (hum bars, very grainy picture) that I had to change something immediately. I got an active transmitter and installed it at the DVR. I read the manual, tried all the different settings, but the picture got even worse after having installed the active transmitter.

 

I then removed both active baluns and tried the passive GE ones again. The picture is still bad, but at least I can see something. It was better than with the active receiver and definately a lot better than with active receiver + active transmitter.

 

I know that the cat5 goes along with 230VAC cable in some places, but I am not sure if this is the reason for the extreme interference that I am getting. Also the sudden change doesn't make any sense to me.

 

Any idea how to fix? I would prefer not to pull new cable, because it is really hard in this warehouse.

[zmxtech 0]

have you tried some different pairs there are 4 to choose from

 

z

[scorpion 0]

Has there been a dry spell, and all of a sudden you have had rain?

 

 

 

If yes, then you have a ground loop problem. This would be where you have several different buildings such as a camera on one building, and the DVR in another.

 

Is this the case?

Then ground loop isolater, or isolate the camera mount from the wall it is mounted to (such as metal warehouse buildings).

 

 

Another thing to do is to kill the power to the cameras, then repower them to see if the problem goes away.

 

If yes, then you may have had a power fluctuation where the cameras went "tilt" when the power came back on.

 

Is this the case?

Then add a battery back up.

 

 

Are you running 12 volt DC, or 24 volt AC?

 

____________________________________________________________

 

Note to others who are coming to this post from a search engine.

 

If you are running cameras a long distance from the DVR then use a very large wire to run power. Use 24 volt AC power. Get cameras that are dual voltage. The cameras will work off of 24 volt AC. At the end of the line where the power has dropped down to lower voltages (lets say 15 volts ac) the cameras will pull the lower voltage, but will convert it internally to DC, and it will be above the 12 DC threshold, and it should work. You will have to experiment what will work best for you.

 

This design is a bandaid, and does not replace good system design.

 

This would be common to large "mini warehouses" where you have a front office building, and several buildindgs to the rear. Most have a "vertical building to the left, and horizontal building at the "top", and another "vertical" building to the right creating a box, and maybe building in the center. It is common to see the wiring going from an office building to one of the buildings on the right, or the left, and to travel all the way around all of the "outside" buildings". The runs can be so long as to cause video problems at the "end of the line".

[koolmer 0]

I don't think its a ground loop problem. The screen is connected to the DVR output and the entire picture is bad. The cameras are ok - if I connect the screen directly at the DVR with a 2m cable, the picture is perfect. The problem is somewhere along the 300m of cable. Too much resistance? But then the active baluns should help, right? But instead of improving the picture, the active baluns make the picture even worse! The cable is cat5e from Excel (UK brand) and I have never had any problems with it.

 

I will try a defferent pair of wires, but I doubt that it will change anything. Any other suggestion?

[WRS_Mark 0]

300m run in a warehouse? Is there any reasonable possibility that the cable was hit or pinched somehow? Perhaps someone drilled through a wall/ceiling, rodents did some chewing, etc? It seems that if the system was working well at first then it usually will continue to work until something is changed.

[rory 0]

also check for any high voltage recently installed near the cable.

[koolmer 0]

also check for any high voltage recently installed near the cable.

 

This could be something that happened. I also think that it has something to do with the 230VAC cables that are next to the cable for about 30 meters. It is probably me who has to re-pull the cable. Is there any device that can handle/remove strong interference.

[zmxtech 0]

The way of finding it would be to use a oscilloscope to see what interference is present on the lines.

 

I have found many problems with data and power running too close to AC power. It induces all sorts of nasties

[koolmer 0]

The way of finding it would be to use a oscilloscope to see what interference is present on the lines.

 

I have found many problems with data and power running too close to AC power. It induces all sorts of nasties

 

I don't have an oscilloscope and have never used one. There is a connection in the middle of the cable after about 175 m. I have connected the screen there and it was ok with the passive balun and good with the active balun.

 

I started pulling a new cable from that location to the screen. Let's see how it is going to be then. Does it make any sense to pull screened cat5? Does that usually reduce interference? I have read somewhere that screened cable is not recommended for baluns.

[koolmer 0]

I re-pulled about 80 m of cable and made sure it is not near any high voltage cable. There are about 4 m where the cable is next to high voltage, but this cannot be avoided. For the other 220 m I used a different pair of the cable.

 

The result of this is a slightly better picture. All hum bars seem to be gone, but the picture is very noisy, like on a TV with an antenna and a poor signal. When I connect the active receiver balun the hum bars appear and picture is really bad.

 

Any other idea what I could try?

 

Edit: Does anyone think a ground loop isolator could help?

 

Edit2: I have connected an active receiver after about 200 m of the cable and the picture was clear. How about installing the receiver there, converting the picture with a passive balun again and installing another active receiver in the final location? Has anyone ever tried this?

[koolmer 0]

Ok - I am still working on it. Now I have installed the active receiver in the middle of the entire cable. About 200 m away from the DVR. The remaining 100 meters go with passive baluns. The picture is MUCH better now - don't ask me why.

 

However, it is not perfect yet and I am going to get another active receiver to install in the final location (screen). So I will have two active receivers and 2 passive transmitters for 1 signal. This should then give a pretty ok picture. Has anyone ever experienced something like this? I wonder why the active receiver hasn't helped at all.

 

koolmer

[Hoops 0]

Maybe you wished to consider NVT's UTP as they virtually guarntee interference and noise immunity using thier passive transmission and active receive up to a distance og 1Km and they also give a lifetime warranty.

 

Ciao,

 

 

Hoops

[Guest]

The way of finding it would be to use a oscilloscope to see what interference is present on the lines.

 

I have found many problems with data and power running too close to AC power. It induces all sorts of nasties

 

I don't have an oscilloscope and have never used one. There is a connection in the middle of the cable after about 175 m. I have connected the screen there and it was ok with the passive balun and good with the active balun.

 

I started pulling a new cable from that location to the screen. Let's see how it is going to be then. Does it make any sense to pull screened cat5? Does that usually reduce interference? I have read somewhere that screened cable is not recommended for baluns.

 

 

Sorry to say that this is the problem with twisted pair transmission.

 

We see many systems that are offering poor quality pictures because the engineer is not trained to install and problem solve such systems.

 

No engineer should tackle such systems without a pattern generator or a oscilloscope and the training on how to use them.

 

These are essential tools of the trade and you cannot set up this type of transmission system without this test equipment.

 

A pattern genenrtor can be purchased for only £120 ($180 USD) and would immeadiately isolate the camera side of the problem.

 

Please, please ask your employer for a training course.

 

It will end up saving him money!

 

Regards

 

Ilker

[koolmer 0]

Alright. Problem solved!!!

 

So - here is the end of the story:

 

I had installed the active receiver in the middle of the cable pull and after the active receiver I again used a pair of passive baluns for the remaining 100m. The picture got better, but still some interference left.

 

I mentioned before that the camera cable is running next to 230VAC cable for about 4m and this cannot be avoided. The power supply of my camera controller (Ktd-405) was plugged into the outlet at the end of this 230VAC cable (besides other equipment of course). Last week the controller failed and I traced it down to the power supply. It was a switchmode power supply, getting very hot. The moment I plugged it out from the outlet the image on the screen was PERFECT.

 

So somehow this PSU has induced interference into the 230VAC cable which then affected the camera cable and caused the noise in the picture. I have learned my lesson, but I really didn't expect that!

 

koolmer