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How do I extend SymLink up to 200 feet?

SymLink is one of the fastest, easiest to use audio busses in the industry, but some integrators want to run SymLink cables longer than the maximum specified length of 10 meters. In the past it just wasn’t possible, but we are happy to announce that this is no longer the case — with a few stipulations.

First, let’s explore some background on SymLink. Put on your propeller caps for a quick cable lesson.

As you may know, SymLink uses standard STP (shielded twisted pair) CAT5 cable supporting up to 10 meters in length. Typical CAT5 cable, by design, has different twist lengths for each pair which means that each pair has a different physical length. This difference in length causes a signal delay difference from pair to pair which is known as skew. Excessive skew between the twisted pairs that carry data and the audio clock can cause a great deal of grief.

Fear not! Your friendly Symetrix engineers have found an alternative solution brought to us from the land of video, a cable that can increase the maximum SymLink cable length from 10 meters to 61 meters, or 200 feet worth of SymLink. Read on for the details…

We’ve tested a new low-skew cable manufactured by Belden, model number 7987. Designed for long distance video runs, Belden 7987 has extremely low skew. It is even available in Plenum-rated and Riser-rated versions. The Belden part number for the plenum-rated version is 7987P while the riser-rated version is 7987R.

To attain SymLink distances of 200 feet, three conditions must be met:

1. You need a cable with sufficiently low skew.

2. Since the Belden 7987 is an unshielded cable, particular attention needs to be paid to the ground potential between SymNet devices.*

3. Lastly, the quality of the RJ-45 connections must be perfect. Sloppy connections or slightly bent pins will reduce the achievable length.

*In our testing of a worst case scenario (one device floating and the other grounded), we measured a ~50 VAC (RMS, measured with multi-meter) mismatch between the devices. However, as soon as a SymLink cable was connected between them, even an unshielded cable, the ground difference was reduced to a few volts. While the SymLink transmitter/receiver chips have some built-in protection to prevent any damage, the long term effects of a large voltage differential between units is unknown at this time.

As always, your mileage may vary. While this revelation in cable technology has proven itself in our lab environment, we can not possibly test all of the unknowns one may encounter in a real-world installation. A little care to ensure that all devices are indeed grounded and all SymLink RJ-45 connections are tight should provide great reward.

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