Cable and Resistance

[cctv_down_under 0]

Can someone explain to me why you can use a barrel joiner close toa DVr witha very short run and it will not affect video but joining in the middle of a cable run does.

 

Surely the resistance does not change, however I have always heard that you can join a cable so long as it doesn't run far from the join.......the maths just doesnt work in my head because the resistance is the same?

[Soundy 1]

I've done just this in numerous installs, I've never noticed a difference. One job, we have three FLIR thermals and a Pelco Esprit atop a 50' tower, all runs up the tower using baluns over Cat5e, then connected with barrels to about 400' of direct-burial RG59 in a weatherproof box at the tower base... there's no discernible issues with this setup, all video is rock-stable (and those FLIRs can be REALLY picky about bad cabling, too).

 

Anytime I've seen problems with barrels, it's simply been a bad connection on one of the two BNCs (ie. a bad crimp, or a corroded/dirty connection). Happens a lot with outdoor splices if they're not sealed well.

[survtech 0]

The location of the barrel connector should make no difference. Soundy's right about the BNC connections. Also, I've seen cheap barrel connectors that don't have gold-plated center pins get corrosion there and lose connection over time.

 

The best practice is to minimize splices wherever possible. For one thing, each connection loses 1/2 db of signal so a barrel adds 1db of attenuation. Plus each connection is an opportunity for a bad connection so a barrel adds two opportunities.

[Soundy 1]

One thing, if you do have to do outdoor splices... I've found it really helps to put a little dielectric grease (typically sold at auto-parts stores for use on battery terminals to prevent corrosion) into the ends of the barrel before snapping on the BNCs. That keeps water and damp air from getting inside the connection (actually, almost any thick grease should work). Using weather-tight compression BNCs is a good idea as well.

 

After that, wrap the whole thing up tight with good-quality electrical tape - it doesn't need a ton of layers if you pull the tape really tight and stretch it a bit as it goes on, so it form-fits better. I've also successfully used a brush-on "liquid electrical tape". I've tried heat-shrink tubing, but the wide disparity in the diameters of the cable and the BNC fittings means it doesn't really seal tight unless you stack several layers.

[survtech 0]

Or try Coax Seal.

 

http://www.coaxseal.com/

 

[Soundy 1]

Nice! I gotta get me some of that!