Video and DC Power by Coax

[PA3CMD]

For a remote placed camera I want to feed the dc Power also via the coax cable.
The simplest way to do this is using an capaitor to block the dc and adding an inductor to block the video.
My question is wat is the best value of both items.
At this moment I am using 1000nF blocking capacitor and 33uH inductor. The image of the camera is walking and i very disturbed.
It would be handy to have a schematic of a working system.

What am I doing wrong and what is the easiest way to solve this problem.

Eim

 

[Skogsgurra]

Assuming that the coax is a 50 or 75 ohms type (like an RG58 or so) then your sync components in the video signals may have a problem with transients between the inductor and cable capacitance. Have you tried reducing Q by adding a resistor in series with the inductor? Also, 1000 nF (1 uF) sounds like a lot to have in the composite video path.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[VEBill]

With raw video (as opposed to RF) I suspect you might require more inductive reactance. The video will have some spectral components at relatively low frequencies. And 33uH isn't much. Perhaps keep the 33uH as the first, but add a much higher value inductor in series. Something to help block the low frequency spectral components.

You'll need to confirm the DC drop through the system to your camera.

Such DC Injectors and DC Blocks for composite video should be available for purchase. How much Googling have you done already?

 

[jimkirk]

If your camera outputs composite video, the luminance signal extends down to DC. You can probably afford to lose some of that.

The vertical sync is about 60 Hz, and you'll need to pass enough of that to keep your monitor (or whatever is receiving the signal) happy. Circuits are available to help reconstruct the sync information.

Also, the absolute DC level is important, and many circuits and chips are available to reconstruct that.

Check out chips from National or Maxim and others. They have some good information and apps notes.

Another way to go, but with some loss of video quality, is to modulate the baseband to RF. (Cheap $10 modulators are available to convert baseband video to channel 3 ot 4.) The RF is much easier to separate from the DC. Then just convert it back.