add video to dc power and then later recover video

Modulate the video and return it on the coax carrying the power. A simple filter should be able to seperate the signal from the DC at either end. I have a 'Channel 3' modulator used for feeding video into a TV set.

Hi Paul

Thanks for the reply.

I Should have told you a little more.

The application is on an articulated truck/lorry. I have to use the existing wiring of the lorry. There will not be any co-ax - well at very small bit at either end.

Thanks

Anbeyon

The other option to Pauls suggestion is to use cat5 cable, and a suitable interface, which if you google for CCTV cat5 will probably eventually give some almost useful hits

martin

Video doesn't travel very well over plain old wires. You could try-- put a 10mH choke at each end of the DC wire, couple the video to the wire in between with a pair of 1uF capacitors.

You'll get *something* out, but it will be rather smeary, fuzzy, and noisy video.

If you don't need a immediate real-time picture, you could use a webcam, and send the data using PPP over the wire, and get pretty good data. But I suspect you need the image right away, not three seconds later. Hard to back up a truck with a 3-second delay!

Must be mid-terms.

Cheers! RIch

then get a 2.4GHz video sender, check out campervan accesories for old gits who can't reverse properly

martin

Then give up, or rewire the truck - you'll never get reliable video to go through ordinary truck wiring.

Good Luck! Rich

The lorry chassis is a bit of a hotbed of electrical noise as it acts like a substantial steel aerial. Also, the chassis loom wiring (electrically) looks like a mass of unterminated, high quality, open transmission lines/resonators that spend their lives singing gentle medium wave tunes to themselves in response to every single transient/ change on the battery/alternator. Sending -clean- 1V video down unshielded wire from say the rear light cluster up through the Suzi connector and into the cab for inductively splitting off, looks a problem. Myself, I'd be looking at a seperate coax feed. john

Probably

Filter the DC out with an inductor.

Try it and see if it works. Ideally you want a piece of coax cable.

The problem with adding DC to the raw video is that video is DC coupled. The filter at the other end will take out the reference to the black level. One could build a circuit to recover it, but that would probably be more involved than RF modulation.

BTW, Martin's idea for a 2.4 GHz wireless link would seem to be the best if one cannot modify or add to the truck wiring. 100% off the shelf solution.

It's a monitor - black level is not such a big deal.

messagenews: snipped-for-privacy@hovnanian.com...

Thanks for all of your suggestions/thought and comments

Anbeyon

On a sunny day (15 Feb 2007 13:24:05 -0800) it happened snipped-for-privacy@btinternet.com wrote in :

One thing you could try is use a 74HC4046, set it to oscillate at about 20MHz, or higher if you can, connect the video the the VCO input, this will give you good linear FM. Add a small inductor on both sides of the supply line, and superimpose the 20MHz. On the receiving side use the same chip in PLL mode with the XOR phase comparator, and grab the video from the source follower output. Watch cable impedance, likely around 100 Ohm.....

Actually in the olden days (1968) I used 2 x 74121 ones hots, byting their tail, with a video modulated current source at about 12 MHz, not the resistor. If you use a low frequency making a low pass will become more difficult.

The FM method keeps DC component, but it will likely be H clamped anyways in the monitor. Works great for audio too.

Well, you'll get a DC component, but it's very likely to wander a bit.

True. Or you can restore the DC level with a diode and two resistors.