CATV Coax Splice

[alokwww]

We're running cameras in our school and one of my friends spliced them together just twisting the together the center pin and the shielding. I told him this was absolutely wrong and would cause lots of signal leakage and he had to put on f-connectors on each end and use the couplers. Am I wrong or is he wrong? Does anyone know of a website that I can print out to show him?
Thanks
-Alok

 

[jeffmoss26]

It may work, for a day. Always use connectors of the proper type. You wouldn't ever just twist the wires together if you were connecting electrical wiring. You would use wire nuts which would be the correct connector. He should have either used F connectors or BNC connectors. Were these security or tv cameras? jeff moss
jeffmoss26@adelphia.net

 

[alokwww]

these were security cameras (CCTV) the cameras themselves are bnc, i told him to just get f connectors and f couplers and conenct them instead of his cheesy splice and to just terminate with bnc where he needs to. im not sure if that is okay to switch between f connectors and bnc connectors. is it?

 

[rpearson]

Definatley not the way to go,especially for a long term installation.Your right he's wrong.

 

[jeffmoss26]

I'm not a video expert so I don't know. It may work depending on the cable size, eg RG59, RG6, etc.
Why does he need to splice anything? Are you extending cable runs for the cameras? jeff moss
jeffmoss26@adelphia.net

 

[alokwww]

yes our runs go roughly 3-400 feet through conduit due to the 24volt ac required to power the cameras so we have junction boxes throughout the runs that were cut to distribute.

 

[daronwilson]

The splice will let signal leak out, and allow foreign signals to enter the system. Looking at coax, remember it is unbalanced, the center conductor carries the signal while surrounded by a shield at ground potential. Anytime you change that, you mess with characteristic impedance of the cable and signal loss will result.

Are you carrying the 24 volts on the coax? If you are, be sure to use solid copper RG-59 or something similar. You need copper braid and a copper center conductor to carry the voltage reliably, don't use regualar steel center RG6.

Good Luck! It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[alokwww]

Thanks for the response Daron. We're running (12 gauge I believe) 24 V AC alongside the coax. Do you see this as a problem which could cause interference. 2 of the cameras are up and running and we didnt see anythign wrong with the signal.
Thanks
-Alok

 

[franklin97355]

You can make almost anything work for a while but if your going to do a job it should be done right then you won't have to go back and fix it. As you add to this system you will at some point find this type of connection causes trouble. Then you will spend the time and expense you saved trying to find the problem. Take this from a school technician where the electricians installed the phone systems. (wire nuts as splices)

 

[daronwilson]

I prefer the seperate power wire myself, we generally run figure 8 CCTV wire with 2 conductors 18 gage for power in one jacket, and the all copper RG59 in the other jacket. I don't believe you will have any problem with interference, not usually a problem.

Normally interference sneaks in when there is a break in the shield and some outside source slips in.

Good Luck! It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[jeffbouldin]

Well this is my bread and butter. I do this day in and day out.

F-connectors are balanced for cable TV(CATV), the signal runs on the sheild. You are running closed circuit TV(CCTV), the signal runs on the inner conductor. You need to use BNCs. You can get two males and a coupler, or one male and one female. The way he has done it will work for awhile, but probably degrade over time. Tape the connection with electrical tape to prevent it from shorting against something.

As for the 24vac you'll be fine. There is not enough voltage or amperage to cause a problem.

 

[InnoTech]

so as jeffbouldin puts it (which is put very well) both of you were wrong!!! if i were you i would just get the BNC's and tell him they are f-connectors!! ;-) "Jack of all trades. Master of none."

 

[daronwilson]

Hmm, I dissagree with a couple points here.

First, F fittings and/or CATV is definately not balanced. Any single center coax is an UNbalanced feedline. Balanced feedlines have two equal conductors (remember the old flat twinlead 300 ohm tv wire?). As far as one type of connector being preferred over another, since you are installing CATV I would stick with BNC. By design, the BNC fitting shields the center conductor better by having a ground sleeve that actually doubles up on the shielding at the connector. It is a far better connector than the standard "F" fitting.

Second, the signal does not run on the shield in CATV cabling. The signal is modulated on the center conductor, and kept there by providing a shield (grounded) around it at a specific distance giving the circuit it's characteristic 75 ohm impedance. In CATV installations, the shield is grounded at the entry to every home (or should be). I do not know of any RF system that carries the signal on the shield of the cable.

If you want to do it right, put in a BNC connector and make the splice with a 'barrel' or put one of each gender of BNC connector in there.

Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com