Is Your HDMI Balun Really a Balun?

I can remember the first time I heard about a Cat 5 extender given the name “balun” - I couldn’t help but chuckle at the use, because baluns serve an entirely different purpose.

I thought that it would get corrected, but I was wrong.

Baluns have been around for many moons, and the word actually came to be as an abbreviation “BAL-UN.” It was a short way of saying “Balanced to Unbalanced,” and was used just in the radio frequency and audio frequency arenas as transformers. Passive in design, these transformers would accept a balanced line configuration at particular impedance and convert it to an unbalanced line configuration to a different impedance or vice versa. At that time it was most popular with RF transmission lines.

The only alternative long-distance transmission device I am familiar with is the Coax 5 wire RGB designs. These convert HDMI TMDS balanced video to an unbalanced format at the source. At the sink the unbalanced is then converted back to balanced.

Category 5/6 extenders are typically NOT baluns. They fall in the category of HDMI Alternative Transmission Devices (ATD). Cat 5/6 extenders in most cases do not use transformers. In fact, most Cat 5/6 extenders do not convert HDMI at all. Their only job is to take balanced line HDMI TMDS video and extend its distance either by way of equalization or some form of data conversion, but they do not support balun rules.

Also, real baluns typically are built as passive devices. Their intention is not to necessarily provide gain, but to correct for impedance matching. So you see my point here. How could anyone come up with an HDMI Cat 5/6 solution and call it a balun when knowing it isn’t. Then again we are assuming they know; now that’s scary!

As integrators expand to commercial or the commercial professionals expand to audio/video, terminology plays an important role in their understanding of new systems.

Do HDMI baluns provide impedance matching? Not really, there is no need to match different transmission lines impedances because Cat 5’s native impedance is already 100 ohms, exactly the same as HDMI.

Do HDMI baluns convert balanced line to an unbalanced format or vise versa? Not necessary; they typically pass through HDMI’s balance line TMDS format.

So don’t think that because you have an HDMI balun you can use it to correct for an impedance mismatch. They are not designed for that. We have seen people in the field in a jam where they must use completely different cable to finish the job and think that the balun will correct for any mismatches. They won’t.