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phantom power for CMOS camers

Discussion in 'Electronic Components' started by Paris, Aug 5, 2004.

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  1. Paris

    Paris Guest

    Is there any way that I can send power down the co-ax video cable to my CMOS
    cameras without destroying them. I know in audio mics this concept is called
    phantom power. Any ideas on how I can pull the same thing off with my board

  2. Mark (UK)

    Mark (UK) Guest


    I know Panasonic did that for some of their smaller cameras, plugged
    into the CCU by just one Coax - no idea how they did it though.

    Yours, Marek.
  3. It would be easy if you RF modulate the signal (use same technique as
    aerial amplifiers). It would be harder for a composite video signal
    as the frequency range is pretty much down to DC, or when image gets
    dark you might find a DC shift through blocking capacitors might lose
    frame hold or similar effects.
  4. There are things for that available, but phantom power is when it's thru
    a center tapped winding of a transformer. You can use DC blocking
    capacitors on each end of the center conductor to isolate the DC from
    the signal, but you have to make them big enough so that the low freqs
    of the video don't get attenuated. The DC is injected thru a higher
    value resistor, several times higher than the usual 75 ohm video cable
    impedance. You can also use a choke in series with the resistor to
    reduce the video going back into the PS.

    There weil be some losses in the cable itself, but a lot more losses in
    the resistors on both ends, so you have to take that into consideration.
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