phantom power for CMOS camers

[Paris]

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
cameras?

Thanks
paristotle

 

[Andrew Gabriel]

In article <bKwQc.31058$Jq2.1477104@news20.bellglobal.com>,
"Paris" <paristotle@hotmail.com> writes:

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
cameras?

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.

--
Andrew Gabriel

 

[Mark (UK)]

Hi!

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.

Paris wrote:

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
cameras?

Thanks
paristotle

 

[Watson A.Name - \"Watt Su]

"Paris" <paristotle@hotmail.com> wrote in message
news:bKwQc.31058$Jq2.1477104@news20.bellglobal.com...

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
cameras?

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.

Thanks
paristotle