Cable Line Loss

[Cpt Rick]

Drax, maybe you can refresh me here, since for the life of me, I can't remember how to figure this out (too many drugs in college)...

I'm running a long input cable from a computer to my mixer (50 ft +). I need the formula for figuring line loss per foot based on cable size to determine what cable to put in, and where exactly to run it to achieve the lowest loss and least noise possible. This is a permanent installation in my own bar.

Thanx.

[Bill Cronheim]

Hello Captain,

Since you're dealing with a lo-voltage signal your line loss will be insignificant.

The quality of your cable will be the most important factor. 22ga. would be recommended.

[DJ Dr. Drax]

Bill is fairly on target. as for the formula for line loss under 100', he is right. Tt line levels, it is an insignificant value.

The things I think that is important is the following.

1.) When ever you have to cross a Power line or a speaker cable do so at right angles.
2.) Use a balanced output from the PC to a balanced input on the mixer. If your PC is unbalanced, either get a Professional grade sound card that provides balanced outputs, or use a direct box. If your Mixer doesn't accept balanced inputs get a direct box for it as well.
3.) Use a grade of cable of at least 22ga. that is 3 wires & a shield. This will provide the best possible performance.
4.) If your wires must run parallel to power or speaker wires, seek to keep at lease a foot of separation at all times.
5.) Avoid locating the wires near any electrical devices such as floodlights, transformers, heater wires, anything with large current flows.

These are not absolutes, but are viewed as the best measures to assure absolute low noise performance when sending line leval signals over long distances.

[ November 01, 2002, 10:00 AM: Message edited by: DJ Dr. Drax ]

[Cpt Rick]

Thanx guys, I will be cabling this coming weekend and week.

It makes me wonder about something else though, my surveillance cameras run at low voltage (1 volt p-p), but the company insists that I install their amplifiers at anything over 300 feet. Does that make sense, or is the distance enough to make a difference?

[DJ Scott]

I have run RG-6 to 1500 feet on black-and-white cameras. Only very slight phase shifting, but VERY slight.

[DJ Dr. Drax]

Rick,

IT really all depends upon the kind of signal.
If your sending this as composite Video, anything really over 50' will start to potentially ghost & get fuzzy.

If it was me I would use the X-10 Transmitters. While you don't have to go wireless, you could, but the built in TX for NTSC Ch 3 or 4 is very good.

You could do that, then use RG-58 coax & go up to about a half a mile. The signal has more integrity when transmitted on a carrier.

A composite or S-video signal WILL degrade & have losses. The difference in the two examples you have stated all has to do with frequency. 50' or so at AF <20Khz the losses are negligible. AT RF >500Khz which is where Composite video lies at around several Mhz bandwidth, the losses & degradation goes up significantly.

[KJDJ]

Baseband out of a camera Video 0-5Mhz. RG-6 .61 Db/100ft loss at 5Mhz.
Composite Video includes audio add another 1 Mhz 0-6 Mhz .69Db/100'

Capt. I add like Drax, use the direct box out of your PC you need the common mode noise rejection that a balanced line gives you. Plus you will get the added electrical isolation safety between the PA and PC.

I personaly don't run more than 3' with unbalanced audio lines with my PA or DJ system.

[DJ Dr. Drax]

Also more important that mere line loss is the signal degradations that occur in RF over distance due to impedance changes. This is the WHOLE reason for coax, to create a uniform line impedance.

[Cpt Rick]

Thanx again Gentlemen. Now for another question [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

It's funny you mentioned X10 Drax, since my whole place is running off it. I have a few of those cheapo XCams (2.4Ghz wireless) besides my standard wired B&W composites. They don't work very well through 18" thick brick walls I've noted. I have two of said walls between my receiver and one of the cameras, plus it's on the first floor (receiver is on second floor). It's actually only about 60 feet straight line away.

Any way to amplify the signal or tweak the antenna on the 2.4 to get better penetration through the walls? I took one of the antennas apart and found two thin copper plates separated by a piece of plastic, but I'm not familiar enough with 2.4 to figure out how to increase the gain.

Thanx, Rick

[DJ Dr. Drax]

Increasing the gain on planar antennae is all but impossible from a mechanics point of view unless you really understand how they work. Most of these types of units are not made for adjustment. Electrically you would need to know a whole lot more to actually add an additional stage to it.

My suggesting them was not so much to use the wireless aspects, but to use the VHF Tx built into every Tx. This would allow you to pump it into a coax cable, that you could run it to anywhere you needed.

You could do this with all the cameras, then run them into a cable switch, then into a receiver to convert it to composite or s-video.

[ November 03, 2002, 03:45 PM: Message edited by: DJ Dr. Drax ]