I have my dvr card set up to only record when there is motion. Lately when there is no motion sometimes the image will start to jerk and the software detects it as motion and starts recording unnecessarily for hours on end. Simply turning off or on lights will settle down the jerky video and all will be normal for a while. I have tried 3 different cameras and they all do the same. It seems to be a problem with the card or some kind of electrical interference but I have not been able to track down the culprit. Any ideas?

If not already done try powering the camera and dvr from the same power source.
Could you post a image?

One of the other cameras that I tried with it was plugged in the same outlet. The third camera I tried actually was running on a battery. The crazy thing actually made it all the way through yesterday without a problem. It is very un-predictable as to when it will malfunction. The next time I catch it I will post a small clip of it.

Could be improper loading on the video feed. On my DVR, I split the camera lines off to run to my test bench, and when I connect them to a box I'm working on, one camera on the DVR jumps all over the place until I disconnect it. Maybe check if your DVR has termination options for the inputs ("Hi-Z" vs. 75-ohm), and if you're splitting the line off to something else, disconnect that.

The card is 4 channel and I usually only use one. Just one cable straight from the card to the camera with nothing else split off. The other 3 inputs can actually be disabled within the software. The video will actually be jerky on any of the 4 ports if I move the cable from one input to the next and so on. Are you saying that I should terminate the un-used inputs with a 75 ohm terminator like the one pictured?

No, terminating the unused inputs will not (or SHOULD not) affect the problem on the other (if it does, there's something very screwy about the design of that card).

Have you tried a new cable run? Even if you just string it across the floor for testing... could be a damaged cable, could be running too near a strong EMI source (lighting ballast, A/C compressor motor, etc.), could be bad connectors on either end...

I've already tried different cables when I tried the other 2 cameras. Last night I ran a drop cord to power the unit from another circuit in the breaker box but still had the same problem all through the night. Tonight I will try actually relocating the pc to eliminate the possibility of it being too close to the possible interference you mention.

I tried to upload two small clips but couldn't. I can email them to anyone interested. One is functioning properly and the other is the shaky video detected as false motion.

Thanks very much for your input. Hopefully we'll solve this soon.

It's always possible the problem is simply the cheap hardware. For an experiment, try plugging a different type of video source, like a DVD player, directly into the card, see if it still has the same issues.

Well, after many hours of relocating equipment, trying other equipment, checking grounds, and unplugging various items around the house trying to find the culprit, I finally found the problem.

I had an X-10 remote transceiver in my attic and another in my basement that I haven't used in a long time and pretty much forgot they existed. Unplugged the one in the basement and the problem got much better. Crawled up in the attic and removed the other and the problem went away all together. It's been running trouble free for several days now.

Duhh...Now, looking back, I don't know why I didn't think about that first. The way the X-10 stuff works is by sending a signal (noise) through the household wiring. I thought it only sent a signal once it received a command from the remote but apparently it puts out some noise most, if not all of the time.

Thanks to everyone for all of the suggestions!