Modulating camera feed


Active Member
Was wondering if someone had any experience modulating a camera feed to be displayed on a in-house CCTV while also sending it to a DVR? I was recently on a job where 4 cameras were coming in and being split two ways. One output going to a PC camera system, and other going to a 4 channel modulator. The only problem was the feed to the PC system was severely degraded after splitting. Taking the splitter out of the loop cleared up the feed. I tried three different passive splitters with the same result, so I don't think it was a particular splitter. It seems to me it would be awful cumbersome to have to amplify each feed before splitting them, so am I missing something? If I was doing this in a SW panel, that would be 4 1x2 amplified splitters, which would take up a good bit of space and add a chunk of change to the equation.

Depending on the PC's video capture card, you may be able to add a loop through card for relatively low $. Install it and feed the modulator after the PC.

I'm not familar with the loop through cards you mentioned. Do you have a link I can look at? Thanks!

A CCTV signal is about 1 volt. I frequently tell people that a pager battery has more power then a video signal. I have never tried to split a video signal but it is typically looped through devices. A video signal needs a 75 ohm terminating resistor at the last device. Years ago CCTV monitors had a switch marked for 75 ohm or HiZ for a loop through connection. In todays world almost all TVs have a video in connection and I have never tried to see if it is terminated with a 75 ohm resistor. A ohm meter can quickly check this.

It might work to modulate the signal into the existing CATV path (change to RF signal) and then loop the video on to the DVR. You will need a notch or low pass filter and a modulator to do this but all TVs will be able to watch the cameras.
Yes you will want to use a loop through output, you want all DVRs to be the first device from the camera.

Once you have a loop out you can do quite a few things.
To add to what Anthony, Gizzmo and Collin said:

Video signals should not be split, as in a tree-like topology. This would cause reflections that degrade the video signal.

Video should be "looped-through", which is pretty much the same as daisy-chaining. The video "network" should look like one long run, with a 75 ohm terminator at each end. Most video sources have a built in terminator.

Unfortunately, most consumer-grade video equipment also have a built in terminator that cannot be disabled. Such devices are what ruin the elegance of the video-network model.

Probably the largest that I have setup was eight to ten monitors and recorders, driven from a video camera over approximately 500 feet. Again, just one 75 ohm terminator at each end, and all monitors and recorders set to Hi-Z.
The other thing used for Video are Distribution Amplifiers or DA's. Very common in old TV stuff. As it's been 10 years since I worked at a station I can't say that they are still in use or not. Grass Valley was the bomb in that space back then.

A brief search shows them all over the place in prices these days, but perhaps something like this if you are looking to get by cheap.

<Not and endorsement of the above product...I have no idea what I am talking about.>
Thanks for the information guys. I was under the impression that a camera feed was like an regular cable signal and could be split/amplified as such. So loop it through the Geovision first then send it to the modulator, correct?

Skibum said:
Get the cheap splitter like chakara suggests. Save $$. :(
The loop through is the smaller alternative price is about a wash, well once you have 4 of those splitter/amps and their shipping anyway. If there is no loop out option for your system then you must use devices like those.