Catapult™ Development

Twisted pair cable was invented by Alexander Graham Bell in 1881. Twisting the wires in a pre-determined ratio creates a magnetic field that rejects noise. Early telephones could transmit a signal several kilometers before it had to be boosted. By 1900, the entire American telephone line network was either unshielded twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometres of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers.

The same unshielded twisted pair configuration is employed in Cat 5 and Cat 6 Ethernet cable. This makes it effective for transmitting audio signals. The benefits of using Cat 5 cable are numerous: the huge installed networks, ready availability from a host of suppliers, and relatively low cost versus using heavy jacketed PVC cable.

Although RJ45 Ethernet connectors are certainly not the most robust, improvements with connectors like the Neutrik Ethercon™ have elevated durability to the level where it has become an accepted solution. And because the inside of the Ethercon is in fact a standard RJ45, terminating the connector can easily be done in any jurisdiction around the globe.

Using Cat 5 for audio

In 2014, Jensen Transformers™ launched a product called the CI-RJ2R that enables two channels of analog audio to be transmitted over Cat 5. During discussions with the Jensen team, the idea came to produce a larger 4-channel version that could be used on a stage. Given that Radial is well known for building durable boxes, this seemed to fit our product range.

We started with a simple 4-channel XLR to XLR system. We soon discovered that in order to transmit 48V phantom power from a mixer to some mics, we needed a ground wire. The good news is that Cat 5 and Cat 6 cable is readily available with a shield. This provided an easy solution to the challenge. We then asked ourselves a number of questions: where would the Catapult be used? And for what application? Would it be to transmit mic signals or line signals? When running longer distances between distant mixers, would there be noise problems?

The more we thought about it, the more solutions seemed to be at hand. Radial is well known for its wide use of isolation transformers and is well versed at building custom audio snakes. So making these options available seemed to follow suit. We then thought about AES signals and figured out that they too could use the Catapult as part of a network. It soon became apparent that several boxes were needed or more specifically, variations of the same basic framework.

After a lot of back and forth discussions, we finally settled upon 6 models: 3 input or transmit (TX) modules and 3 output modules. The input modules would have mic or line inputs and have thru-puts to feed local devices such as a monitor mixer or recording system. The output modules or receivers (RX) would have split outputs to allow the system tech to further split the signal to feed two systems. In other words, the open ended design would provide complete flexibility.

We then added options for either line level or mic level transformers so that either type of signal could be employed. This would enable the audio company to carry a variety of modules and simply select the one that is appropriate for a given application.

Finally, and probably the most difficult challenge of all, was figuring out a mechanical design that would enable the Catapult to actually be built. With XLR connectors on both sides and an internal circuit board, a special design was needed. This resulted in a split-flanged top cover design that provides the much needed rigidity, while allowing our production team to actually manufacture the device.