Can I Use Twisted Pair Balun For Hd Over Coax Camera

Matt Ion

In answer to Undisclosed #2 | 06/03/16 03:55am

Also, what do y'all recollect isolation transformers exercise and then?

Video baluns are not the same equally sound baluns. Audio baluns ARE isolation transformers. Your typical video balun is non.

Typical audio balun schematic (though they have the impedences reversed - the RCA side is hullo-Z while the XLR side is 600 ohm):

Typical video balun schematics:

If what you lot were maxim was true then there would not be any basis loops with one camera and recorder.

There aren't... at least, not due to the use of video baluns (there are plenty of other possible causes). As I already stated, one photographic camera - no trouble. As you lot add cameras, the problem becomes worse. And it ONLY happens (in my experience) on cheap cameras with a shared video and sound footing, and a shared power supply. Dual-voltage cameras, no problem. AC-only cameras, no trouble. 12VDC cameras with regulators, no problem. Anything that isolates your power connection's ground from the video connexion'due south ground, eliminates this effect.

See, I came from an audio background, live and studio. I was very familiar with audio "isolation-type" baluns. I've also used isolation transformers in motorcar sound to interruption ground loops.

So when I discovered this trouble on a system using baluns and a buttload of inexpensive cameras, I couldn't effigy out why it was happening, because I figured video baluns were isolation transformers as well. But I besides noticed, on this particular site, that when I took cameras off the power can and gave them their ain 12V wall wart, they cleaned right up. Cameras still on the can - racket; cameras on separate power, no dissonance. Two cameras on a wall wart gave a trivial noise. 3 got even worse. In short, whatsoever fourth dimension multiple cameras shared a ability connexion, they got noise. Anything not on that same power was fine.

Later on I bought a couple dozen super-cheap "baluns" my buddy came across... they didn't work, so I took one apart to encounter how they were wired: it substantially matched the first diagram I have under video baluns. I metered it... yup, resistance from one balanced pin to the coax eye pin, but infinite resistance measured betwixt pins, and between eye pin and shield on the coax side - not what you would expect from an isolation transformer. So I looked up video balun schematics, and there they were...

Look, in a perfect world, yous DON'T want DC from the power supply traveling in the coax.

Of class you don't. But when the photographic camera uses the same ground for power and video, that'southward what happens, whether you want it or non. And that's why CHEAP cameras take this trouble.

Its the DC in the coax that gives you the artifacting you run across in the screen.

You lot are literally looking at the electric current flowing between the two different ground potentials.

Yes you are. Differing potentials acquired past the (relatively) massive DC resistance introduced by the balun designs shown above, where a coil is inserted in-line with the signal.