Firewire or Y/C

[oco]

What is better? (quality of signal, speed of switching...)
To connect 3 studio cameras (JVC GY-DV5000) on VT3 on 3port firewire card with firewire cable 'TecNec - DV-DV-164foot' (110$)
or on Y/C connector with Y/C cable. Distance is 30 - 50 meters.

[jcupp]

Y/C = fewer things to go wrong and lower latency

Fear not the analog, grasshopper.

[mgrusin]

Huh, latency aside (T3 is supposed to be better at this than T2), I'm guessing that the Firewire would provide better quality at long distances.

Firewire is (to the best of my knowledge) a twisted-pair differential signal which makes it good for long distances and rejecting interference. Analog will have voltage drop and suck up electrical interference the whole way. Digital will suck up interference too, but by its nature the signal will stay "intact" longer (it will still turn entirely to mush at some point).

Definitely check the specs for Firewire and see if it's rated to run at that length; as a desktop bus it may not be up to it. That's a pretty serious cable run for any high speed low level signal (except fiber); you might need some sort of booster or repeater to get it to work.

Good luck, -MG.

[ScorpioProd]

Yeah, some companies make "special" long length firewire cables that are supposed to work fine, but the real spec for firewire is A LOT shorter than that, AFAIK.

I've had no problem at those lengths doing composite cable runs.

For those kind of lengths, I think I would lean toward the Y/C versus firewire. There are firewire repeaters that can be bought though. With that I guess I would lean to firewire.

Thing is a little analog degradation will look better than a little digital degradation. Since if you see digital degradation, you don't see your signal.

Also, for switching live with VT[2/3], the analog inputs will still have the lowest latency and be the best way to switch live, AFAIK.

[EanJay]

I would also go Y/C, signal loss on a couple of hundred feet of good coax (Belden 8281) is only a couple of db at the most. Easy to make up good quality Y/C cables for long runs.

Not sure of the specs. on firewire for 'video', or on the cable that is sold for this purpose, but standard firewire use to be limited to about 15 feet?.

EanJay

[Paul Lara]

Originally posted by EanJay
...firewire used to be limited to about 15 feet?

It still is.
You can, however, link cables together with a Firewire repeater (http://www.macally.com/spec/firewire/connecting/fh110.html).

That said, I'd also recommend Y/C over 1394. ;)

[EanJay]

Well if you wanted to convert to anything, in order to run camera cables over long distance, might as well convert DV or composite/componant to SDI at the camera, then SDI back to DV or whatever at the switcher. Distance would not be a problem - SDI would get you over 800 feet. This asumes money no object - any convertion tend to get costly compared to the price of good coax.

EanJay

[mgrusin]

The pros have spoken. ;) If firewire is only spec'd for 15 feet, I'd be wary about trying to get it to work at 10 times that length. As said, be sure to get good quality cables. A distribution amp at the camera end may help too.

Good luck! -MG

[vanguard]

When we do long runs we use good 'ol composite.

Why? , well we put an adjustable DA at the camera end to drive the video level/chroma comp to correct levels at the receiving end of the signal (over 700' away for the pitcher POV at a baseball game.

You could use Y/C for the same thing, but would need to find a way to increase the signal at the source (NEVER at the switcher end, you'd be amping the noise as well as the signal).

Also Y/C cables tend to be more fragile than RG series cables.

Somebody mentioned money no object:

Get triax cameras, and remote CCUs.

Frankly, I find the 1394 artifacting annoying enough. Almost as bad as MPEG2, so I would stay away from 1394 as a long-run signal path for the reasons posted above.

If anybody is interested, I'd be happy to post the specs for signal loss for RG series cables, and explain why 1394 gets flakey after 3m...

[Paul Lara]

Originally posted by vanguard
When we do long runs we use good 'ol composite.
...
If anybody is interested, I'd be happy to post the specs for signal loss for RG series cables, and explain why 1394 gets flakey after 3m...

Yes, Jerry, I would!

[vanguard]

OK there are generally two types of "video" cable in use:

8281 - Which is the "precision" cable... (also suitable for what is now SDI, and by the way also referred to as RG-59) This is a double shielded cable which is used in large (read: expensive) facilities... Like your local network affiliate.

RG-59 - The stuff you probably have around your place. (actually 8241, but only called that when talking to Belden...) Usable for digital, but in short lengths only.

So the losses table is like this:

8281 (RG-59)
@ 1MHz .25db/100ft.
@ 10MHz .78db/100ft.
@ 50Mhz 1.70db/100ft.

RG-59 (8241)
@ 1MHz .6db/100ft.
@ 10MHz 1.1db/100ft.
@ 50Mhz 2.4db/100ft.

So with the stuff you have lying about, you need about 150' to have 1db (half the input) at video's approximately 4.5MHz signal frequency.

Of less interest now that we all own VTs (because they automatically time everything up) is the time loss/SC shift for a given length...

For Example:

8281

Time | Length
nsec | feet
1 | .77
2 | 1.54
5 | 3.84
10 | 7.68
50 | 38.4
100 | 76.8
500 | 384
1000 | 768



RG-59 (8241)

Time | Length
nsec | feet
1 | .65
2 | 1.30
5 | 3.25
10 | 6.50
50 | 32.5
100 | 64.9
500 | 324.5
1000 | 649

NTSC subcarrier frequency is 3.579545MHz, or one cycle of subcarrier approximately every 0.0000002793 seconds. Thats one full cycle or 360 degrees, so one degree of subcarrier is .776 nsec (rounded a bit)

So:

8241 in feet | RG-59 in feet | Deg. SC
.5 | .6 | 1
2.5 | 3.0 | 5
5 | 6 | 10
25.2 | 29.8 | 50
50.4 | 59.6 | 100
181.3 | 214.6 | 360

This is why discrete Frame Synchronizers were soooooo important way back when... And to us old-hands the VT is soooo cool.

Imagine in our old linear suite we had a "delay room" where (large) loops of cable were hung to get things to arrive at the switcher on time! Literally hundreds of feet long. All to make stuff the correct color, and to have the fill for a key match the hole that was cut.

Ahhh

Oh I almost forgot, why 1394 gets flakey:

OK the 1394 signal is like any other digital signal in that it is VERY sensitive to timing along the data stream.

Now imagine the 1394 cable in your hands had no connectors, and was inside a perfectly shielded environment. The only losses would be from the wires themselves.

Now plunk two connectors on there, you just zapped 2db of signal before plugging it in!

Now plug it in, whoops there goes 2db more.

So we are down 4db already.

Now run that signal.

The signal hits the connector and wham .5 (or so) db of that signal is reflected (not absorbed!) back down the line! Bouncing off the incoming signal (and "denting" it on the way).

These echos are like multipath in a transmission through the air system.

Broadcast analog TVs showed us these with ghosts of the main signal. (BTW this is why the current DTV standard is soooo wrong...)

Basically without getting more sillier than my tangent has already gotten:

The signal strength of the 1394 (transmitter) source isn't enough to overcome cabling losses, and not sturdy (or filtered) enough to withstand SWR (reflected signals) on long runs.

The losses are the main problem, being chased by the SWR which will cause intermittent data loss, and blank screens....

Whew!

OK I'm done now. Tired yet?