Why do Video Switchers Need Power?

[Outland]

I was looking at a few composite video switchers, and I noticed that some of them (such as this one) need separate power.

What is the power for? I would assume all it's doing is mechanically making contact with the different inputs and outputs. Others don't need power at all.

[Celt]

Mechanical contact switchers don't need power. Electrical ones that use relays or some other scenario, do.

[CoogarXR]

I had one similar to that Archer. It has a built-in signal amplifier. Those are more like a matrix switch, any input can connect to any output. If you think about it, say you have a VCR connected to an input. Then you select that input on the other 3 dials. That signal is split 3 ways. It has to be amplified or it would get dimmer with each output you add.

If it was just one input selected to one output, then you wouldn't need an amplifier. But to send it across potentially multiple outputs, it needs an amplifier.

[Dave A]

Simple mechanical switchers like the Archer are just that. They change when you move the switch regardless of where the scan on that frame is. In the middle of the scan or wherever...it just changes and hopefully your recorder does not belch on the non-standard change. You could do the same with ganged light switches.

A real electronic switcher of the analog era waits to the end of the current scan and makes the change, so as to not disrupt the full scan, at the vertical interval point in the scan. No roll, no re-lock, and sync changes with the video...very clean and coordinated with the next frame. Sync rules in this scenario.

[Outland]

Great information.

Dave, the Archer does have a power cord. Did you mean to say that if it didn't, it would be a mechanical switch, or is it indeed an electronic switch due to the presence of power? Or is it simply a mechanical switch, but amplified as Coogar said. Does amplification/waiting for sync have any effect on image/audio quality?

If not, what would be an example of an electronic switch from the '80s or '90s era?

[Dave A]

It still needs power for the pilot lamp and the video path and any processing. All are electronic. This is a mechanical switch trying to live in an electronically synchronized world. A live change from one source to another DURING a recording will upset sync as the video may change mid-scan and not lock right away to the new sync unlike a modern switcher that waits to the end of the frame/sync to do the switch. If you use it only for a one-pass recording, you should be fine. Think of this as more like a router than a switcher.

[ppppenguin]

I have designed video switchers for professional/broadcast applications (up to 64 in, 64 out) so am aware of the requirements.

The first problem is that if you have more than 1 output and wish to connect one input to more than 1 output you need an amplifier. This is simply because video inputs are (should be!) terminated in 75 ohms. If you don't have an amplifier you will connect multiple 75 ohm loads to one source resulting in wrong signal levels quite apart from any impedance mismatch.

The other question is timing of the switch. This has been mentioned here but the explanations aren't entirely correct. In a broadcast environment you try to keep signals synchronous, in other words with their field syncs at the same point in time. Hence you can switch between them freely without causing sync disturbance. The switch is usually done on a specific line in the field interval https://www.document-center.com/stan...8/history/BASE

In a domestic environment the various signals are not synchronous so you might as well take the switch at any random time. You'll get a disturbance regardless. If you wish to switch between non-sync signals without disturbance you need a frame store synchroniser.

[Damnation]

Also keep in mind "powerless" switchers tend to suffer from degradation of video (and probably sound) quality.

[dieseljeep]

Originally Posted by Outland

Great information.

Dave, the Archer does have a power cord. Did you mean to say that if it didn't, it would be a mechanical switch, or is it indeed an electronic switch due to the presence of power? Or is it simply a mechanical switch, but amplified as Coogar said. Does amplification/waiting for sync have any effect on image/audio quality?

If not, what would be an example of an electronic switch from the '80s or '90s era?

I have a Radio Shack branded video switcher and it has some kind of an IC, that does the switching. This one switches the RF inputs, VCR, cable antenna, etc. One of the inputs was dead from a spike???
I was able to order the chip from RS. It was like $1.25 each, I bought two.
That's when RS was a real store and not a cell phone peddler. Very good support!