Advisory: Baluns Versus Adapters

From Steve Lampen, PLM VSS  steve.lampen@belden.com

There are lots of other people who believe attaching some Category 5e UTP to anything will make it work better. Such is not the case. All ‘category’ cables require that they be driven as balanced lines. That’s why, when Cat 5e or Cat 6 cables are used for audio or video cables, where those signals are not balanced lines, you need a ‘balun’ to match that balanced line to the unbalanced source. BALanced to UNbalanced, as the name implies.

For quite some time, a few manufacturers have been making adaptors that fit into faceplates that start with RCA plugs (unbalanced audio or video) and convert those to an RJ-45 or punch down strip. This “implies’ that you can punch down any cable and it will work. But these adaptors are not baluns. You can tell because there’s nothing in there except wires, no transformers, no other parts.

What these adaptors do is unbalance the balanced pairs they are attached to. Those pairs then lose all the noise rejection they were designed to provide. It also severely limits the distance you can go. With RCA-based audio, for instance, it begins to affect the audio around 30 ft. Now, if they put an actual balun in there, you maintain all the natural noise rejection of a twisted pair, and you could go hundreds (even thousands) of feet.

The real problem is that, when these adaptors are used, and the sound is terrible or the circuit is noisy, they most often point to the cable. Or, you might tell them, “Oh, that’s because you’re not using Belden cable, with bonded pairs…etc. etc.” But, when they subsequently purchase a Belden Bonded-Pair cable, guess what, it won’t work either. Because the cable is not the problem, it’s those adaptors.

So, if you see faceplates with RCA connectors on one side and Category cable on the other, have a real good look inside that module! If it’s just wires, warn them! You could be saving that customer a real headache!

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Steve Lampen has worked for Belden for 18 years and is currently Multimedia Technology Manager and also Product Line Manager for Entertainment Products. Prior to Belden, Steve had an extensive career in radio broadcast engineering and installation, film production, and electronic distribution. Steve holds an FCC Lifetime General License (formerly a First Class FCC License) and is an SBE Certified Radio Broadcast Engineer. On the data side he is a BICSI Registered Communication Distribution Designer. His latest book, "The Audio-Video Cable Installer's Pocket Guide" is published by McGraw-Hill. His column "Wired for Sound" appears in Radio World Magazine.