Coax Modulator

[bh00]

Hi,

Many CCTV systems use stuff like this: https://www.electro-tech-online.com/custompdfs/2009/10/ASTVDS2730_en.pdf to send power, data and video over a piece of coax.

Does anyone have any ideas or circuits on how I can make my own version?

Thanks

 

[Nigel Goodwin]

It's just a question of filtering, the signal and power are combined and separated by a simple capacitor and choke at each end.

 

[bh00]

Thats what I thought at first. I can understand how to do power by just DC coupling. But most of them translate RS485 into something, as well as video? Do they need to use modulators and demoduators? WHat frequencies would be split?

 

[Nigel Goodwin]

Easiest way is to use an RF carrier, for example a Sky satellite receiver sends out both DC (to power a 'magic eye' or amplifier) and a UHF TV signal to feed a TV. At the same it also receives an HF signal carrying the remote control data from the 'magis eye'.

 

[bh00]

i see, so using capacitors and some modulators, i can modulate the frequency of comms one way to a certain frequency, comms the other way to another, and the video signal to a uhf frequency, finally the power can be dc coupled in? is there any way to modulate many video signals on together?

 

[Nigel Goodwin]

i see, so using capacitors and some modulators, i can modulate the frequency of comms one way to a certain frequency, comms the other way to another, and the video signal to a uhf frequency, finally the power can be dc coupled in? is there any way to modulate many video signals on together?

Stick them on different carrier frequencies - just like on analogue cable, or an aerial distribution system

 

[bh00]

ok ill take a look for some suitable circuits.
what kind of quality losses should i be expecting however?