Light horizontal scrolling lines

Actually that's a pretty good picture - especially from $65.
Hey - someone stole your jetski ;)

Sounds like A/C hum or a ground loop. A piece of lumber is invisble to RF so a stud inbetween Cat5 and A/C won't shield the noise.
 
DavidL said:
Actually that's a pretty good picture - especially from $65.
Hey - someone stole your jetski ;)

Sounds like A/C hum or a ground loop. A piece of lumber is invisble to RF so a stud inbetween Cat5 and A/C won't shield the noise.
Actually, it's my Seadoo Utopia 185 Jet Boat and it's still on the lift at the lake. I'm hoping to get one more hot day for a nice fall cruise before I take it out of the water and officially declare summer dead for 2005.

Could you explain what a "ground loop" is and what might cause it?

Thx.
 
Man, I looked with my reading glasses, I blew the images up to full screen, and even enhanced them in Photoshop, and I can't see the darn problem. My eyes must be getting old. I'm sure they are obvious when they are moving.
Could you explain what a "ground loop" is and what might cause it?
A ground loop is when a circuit is tied to ground in two separate places, causing current to flow through the ground. An example: If the power-supply to the camera has the negative of the DC tied to ground (unlikely, but possible) then the shield of the coax is tied to that ground as well. If the shield at the capture-card is tied to the computer's ground (likely) then the shield of the coax is tied to ground at two places. If there is any difference in potential between the two grounds (always the case, impedances being what they are) a small AC current flows through the coax, causing an AC hum on the image.

If the image is a single band that gradually gets lighter, and then darker again over about half the image vertically (all of the image, horizontally), that is very likely 60 Hz hum.
 
rocco said:
Man, I looked with my reading glasses, I blew the images up to full screen, and even enhanced them in Photoshop, and I can't see the darn problem. My eyes must be getting old. I'm sure they are obvious when they are moving.
Ok so it isn't just me, I thought those pictures were perfect as well ;)
 
I'll have to post a link to a video captue. The bands are easy to see "live" (especially in low light) but hard to see in still captures. Rocco, thx for the info. Any idea how to fix the ground issue if it is at the capture card?
 
jeffx said:
Any idea how to fix the ground issue if it is at the capture card?
Finding a ground loop isn't very difficult if you have an ohm meter or continuity checker, but it can be time-consuming. I would try it with everything powered off. Based on the symptoms, I would also concentrate on the shield of the coax.

Check the continuity between the coax shield at the PC and the PC chassis. They will likely be connected. If not, a ground loop looks less likely.

If there is a connection, then that's pretty normal. But now we need to make sure that it is the ONLY ground connection for the shield. At one of the cameras, check for continuity between the shield and each power pin. There is a strong likelihood that the shield will be connected to the negative terminal. If not, you don't have a ground loop, unless the shield connects to ground somewhere else along it's run, like at a lightning arrester.

If one of the power pins is connected to the camera's shield, then you are tying the two shields together by using a single power supply. That may or may not cause a problem, depending on what happens at the other end of the cables.

But now you have to check the cameras' power supply. Depending on it's design, the power-supply's power cord may have two or three prongs. If it is designed to have two prongs, then it is isolated, and you should not have a ground loop at that point. If it has three prongs, you need to check whether the ground prong is connected to either power lead. If it is, you have a ground-loop between your computer and the cameras' power-supply.

The best solution to a ground loop is to get the grounding correct. If for some reason you can't, as a last resort a video-isolator (often called a "humbucker", after a company that makes guitar pickups) can be put in-line to 'break' the ground loop. Video professionals always have an isolator with them for ground-loop 'emergencies' and for testing, so it may be worth getting one to try. It can often come in handy.
 
The video isolators completely crushed the image. Could this be because the isolators are the wrong frequency range? Or possibly the signal from the camera's needs to be amplified? I guess the lines aren't really that bad and I can live with them. Maybe I was expecting too much from an 8 port $140 capture card.

When I view the same camers through one of my TV Tuners' capture ports, there are no lines.

Here are the isolators I bought:

http://www.partsexpress.com/pe/showdetl.cf...tnumber=180-075

Funny thing is, I tried running my cable connection through one of these into my TV Tuner card, and it completely killed the TV image also. Can someone recommend a higher quality Ground Loop Isolator?
 
Yep, wrong isolators.

Those are meant for cable frequencies, not video, despite the description on the web page. The F-connectors give it away.

When I get a chance, I will lookup some others. The ones that I use are big, square, low-loss transformers, at about $150 each. Too expensive for casual use.
 
For what its worth, there is an old tech trick of combining two transformers to each other, 75ohm to 300ohm and 300ohm to 75 ohm. We used them in a pinch.

I can't find a diagram online anywhere, but here's some pics of whats needed.

http://www.pigselectronics.com/graphics/large/Vt375.JPG
http://www.atariage.com/howto/images/uhf_adapter.jpg

It's F connector to pig tails to pig tails to F connector, but I think you get the idea.

Now that i'm thinking back I seem to remember someone mentioning this was RCA or BNC so i'm sorry if this post is not as helpful as I imagined it.
 
It's been a while, but the scrolling line issue is starting to bother me again. I just stumbled upon some information that I had not read before:

"COAX with copper braid should be used for CCTV."

So, it looks like I'm going to buy some copper braided RG-59 and rewire the 3 cameras I have with this issue.

I found a 500' spool of copper braided RG-59 siamese here for $95 that I may try.
 
I've been using very similar siamese cable, and I can't say enough about how happy I've been since I switched from separate RG6 and power wires. For one, the wires are are lot more flexible and easy to route. And it cleaned up my videos quite a bit.

I did learn from one CCTV installer that for very very long installations, its best to use 24VAC, and the use a 12VDC transformer close to the camera. Apparently AC current travels long distances on cheap wires better than DC.
 
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