Cat5 baluns

[kempelen 0]

I have a couple of BW bullet cameras which produced a very good picture when connected directly to a monitor.

They were not cheap but I think the price was mainly due to the exview chip used because as it turned out the manufacturer had cut cost by using the same ground wire for both the power and video. But this is not a commercial project so I was not too worried.

 

Anyway, I connected the cameras to a cat5 cable about 100m long using a couple of passive baluns.

The image I got was horrible. There was a ghost image rolling across the video and the image itself looked like I was seeing double.

 

After reading some posts on this forum, I connected a separate power supply to each camera but the difference was almost none.

I then opened up the balun on the camera side and it turned out that it was basically just a wire between a BNC socket and a pair of terminals. So I spliced the camera wires directly onto the cat5 wires. It made no difference at all.

 

I should also mention that the cat5 cable is in the same conduit with a couple of 12 and 24 volt wires (both AC and DC) but even when I turned everything else off the image did not improve.

 

I would like to stick with these cameras but I am running out of ideas what else I could try.

I read people's comments on using the cat5 cable and they all seem very positive.

 

Could it be the cheap baluns causing the problem? Or is there really no hope for this setup?

[Soundy 1]

I have a couple of BW bullet cameras which produced a very good picture when connected directly to a monitor.

They were not cheap but I think the price was mainly due to the exview chip used because as it turned out the manufacturer had cut cost by using the same ground wire for both the power and video. But this is not a commercial project so I was not too worried.

 

This is actually very common in low-to-mid-grade 12VDC cameras. You only start getting away from it in cameras that have built-in regulators, which most often means dual-voltage or 24VAC-only models.

 

I then opened up the balun on the camera side and it turned out that it was basically just a wire between a BNC socket and a pair of terminals. So I spliced the camera wires directly onto the cat5 wires. It made no difference at all.

 

Could it be the cheap baluns causing the problem?

Bingo!

 

In fact, if it's just a pair of straight-through wires, what you have isn't even a balun; it's a half-assed adapter and nothing more. If you paid more than $2 for it, you got ripped off.

[survtech 0]

Bingo!

 

In fact, if it's just a pair of straight-through wires, what you have isn't even a balun; it's a half-assed adapter and nothing more. If you paid more than $2 for it, you got ripped off.

+1

 

A balun should have a transformer in it.

[kempelen 0]

Aha! Thank you very much for the info.

 

Just a quick question.

The baluns came in pairs, one of the pair was the one I just described and the other of the pair actually does have something looking like a transformer inside.

If I take two of those baluns with transformers and use one near the camera end and the other on the monitor side, will that work?

 

I guess what I am asking is should there be a transformer on both ends or just one?

[Soundy 1]

The term "balun" comes from "balanced/unbalanced". Regular composite video cabling is unbalanced. What the balun does is create a balanced connection over the wire, which allows it to better reject and/or cancel noise. When you don't have a balun at both ends, the line isn't properly balanced.

 

Switching which end the transformer unit is on, MAY improve things, but it's still not a proper balanced line. Ideally, yes, you need the transformers at both ends.

[kempelen 0]

Thank you again.

 

I installed baluns on both ends and this time I made sure they actually were proper baluns.

The image has improved significantly but not completely. The rolling ghosts disappeared but I still had double image and a slight periodic flicker.

 

I searched through the forum and I believe this was caused by a ground loop.

 

The next thing I did was made sure that no other cameras were connected to the DVR (a PC DVR card actually). I should mention that those cameras were connected to a different power supply, but I guess the ground ended up being the same inside the DVR card.

This removed the image flicker but the double vision remained.

 

As a last test I used a coax cable of the same length and this finally resulted in a decent picture.

 

So it would seem that if the camera shares a common ground, it is next to impossible to use it over a Cat5 cable.

Or is there some device I could add to fix the problem?

 

One other thing I am going to test is to run +/- power over a twisted pair directly to the camera's location. Then use another pair to run the video and ground back to the DVR over baluns.

Because at the moment I have a twisted pair running video and ground to the camera and a single wire running the + power. Maybe that is the problem?

[Soundy 1]

Ummm, wait... you're using the video ground, through the balun, as your power ground as well?

 

Yeah, that would definitely be a problem.

 

If you're using Cat5, try using one pair for the video (I use blue), one pair for power ground (green), and one pair for power "hot" (orange).

[kempelen 0]

Something like this?

 

|--------------|                                                                            |--------------|
| DVR          |                                                                            | CAMERA       |
|              |   |-------|                                               |-------|        |              |
|    VIDEO_________| BALUN |                                               | BALUN |________|_____ VIDEO   |
|              |   |     + |------------------ BLUE -----------------------| +     |        |              |
|    GND  _________|     - |---------------- BLUE/WHITE -------------------| -     |____.___|_____ GND     |
|--------------|   |       |                                               |       |    |   |              |
                  |-------|                                               |-------|    |   |              |
|--------------|                                                                        |   |              |
| POWER SUPPLY |                                                                        |   |              |
|      GND_____|_______/------------------ GREEN -------------------------------\_______|   |              |
|              |       \---------------- GREEN/WHITE ---------------------------/           |              |
|              |                                                                            |              |
|              |                                                                            |              |
|      VCC_____|_______/--------------------- ORANGE ---------------------------\___________|______ VCC    |
|              |       \------------------- ORANGE/WHITE -----------------------/           |              |
|--------------|                                                                            |--------------|

[Soundy 1]

Exactly.

[CCCmarine 0]

Im curious on this one as well........below is the camera we are using Pelco CCC1370

 

From the power Supply 24VAC & COM is two combined pair going to the 24VAC on the camera.

 

Balun uses one pair to each BNC connector. What am I supposed to be running to the GRND ? Should I use the combined brown to a ground in the power supply? I thought I had this figured out until I came across this thread....

 

 

I am using these baluns: http://www.digimerge.com/video-balun-p-160.html

Thanks..

[kempelen 0]

I am sure someone will post a better reply but it was my impression that the replies here were related to DC power, not AC since AC would not suffer from interference as much as DC would.

 

I don't think AC will need the GRND terminal connected unless it is meant to ground the video signal somehow?

 

By the way, even with the setup mentioned in this thread I was getting ghosting etc although not as much.

I ended up going with a coax and that solved my problem.

[Soundy 1]

Im curious on this one as well........below is the camera we are using Pelco CCC1370

 

From the power Supply 24VAC & COM is two combined pair going to the 24VAC on the camera.

 

Balun uses one pair to each BNC connector. What am I supposed to be running to the GRND ? Should I use the combined brown to a ground in the power supply? I thought I had this figured out until I came across this thread....

 

 

I am using these baluns: http://www.digimerge.com/video-balun-p-160.html

Thanks..

Your wiring is correct; ground connection is not needed. It's on there to meet a certain spec, but I've never once used it.

[Soundy 1]

I am sure someone will post a better reply but it was my impression that the replies here were related to DC power, not AC since AC would not suffer from interference as much as DC would.

Neither is affected by "interference" as such. Where the problem arises is with cheap DC-powered cameras that use the same ground connection for video and power: with baluns, the video ground connection then passes through two transformers (one at each end), which makes it substantially longer wire path. You then get two separate ground paths between the camera and the DVR, one of them much longer than the other... and that leads to ground loops, especially as you add more cameras.

 

Better cameras with regulated supplies, including dual-voltage and AC cameras, avoid this because the video and power don't share their grounds.

 

I don't think AC will need the GRND terminal connected unless it is meant to ground the video signal somehow?

Again, the GND is there to meet UL spec. It will almost never be used in common practice.

 

By the way, even with the setup mentioned in this thread I was getting ghosting etc although not as much.

I ended up going with a coax and that solved my problem.

Probably the result of using cheap baluns.

[CCCmarine 0]

Thanks, great info!