Why Rane’s HAL System RADs & DRs Require Shielded CAT 5e Cables

Shielded CAT5e or better cable for all RAD and DR devices is required solely to satisfy the high-frequency emissions and susceptibility requirements of government (FCC) and commission-based (CE) regulatory agencies. If you use unshielded cable at an installation, you are improperly installing these products, and violating the approved use restrictions in the US and CE countries. Shielded RJ-45 connector

Keep in mind, however, that the audio in the HAL System will function without degradation with your illegal unshielded cabling – at least in the audio band. Nearby high-frequency devices may encounter interference – especially in the 6 MHz band. Here’s why:

Ethernet and many other data signals transported over unshielded CAT 5e (or better) cables is random and bursty. There is no fixed carrier clock. This means there is a very considerable reduction, or complete lack of data transitions when no data is sent. Thus, no emissions.

Equally important, some of these encoding schemes are specifically optimized to randomize the transitions between ones (X volts) and zeros (-X volts). Ethernet is typically plus or minus 1 volt and sometimes as small as half a volt. Just like Ethernet, RAD and DR data & digital audio is balanced differential – plus or minus some number of volts. Rane’s RADs and DRs happen to use plus or minus 2.5 volts.

Pros & Cons of 6 MHz

All RAD audio data is also balanced differential AES3: 24-bit, 48 kHz. When transporting AES3 encoded data, there is no reduction or randomization of the transitions and a constant 6 MHz clock is always being sent down the cable – even when no audio is being sent. Thus, the 6 MHz signal and the requirement for shields for EMI reduction purposes. This AES3 is both a pro and con. The con is, the 6 MHz EMI. The pro is, installers and consultants (and Rane telephone tech support) can know for 100% sure that audio is successfully being sent to each and every room in a building using RADs. See Halogen’s Get on the Plane Indicator.

There’s another quite major pro for sound system designers. This relatively low 6 MHz maximum data rate means that RAD and DR cables can traverse punch-down blocks, and RJ-45 patch bays are also easily permitted.  You can’t do this with most Ethernet transports these days – especially Gigabit Ethernet. This also means the bend radius minimums are quite relaxed for RAD and DR cables. These cables can also be longer-than-Ethernet transport: 150 meter (500 feet) RAD, and 300 meters (1,000 feet) DR maximum lengths are supported.

Shielded CAT 5 cable foil with drain wire

To Ground or Not to Ground

Unlike transformer-isolated Ethernet where there’s no ground reference, RADs and DRs are ground referenced and therefore not isolated. Isolation does not reduce emissions or susceptibility from EMI. Ground terminations at both ends of RAD and DR cables do. For example, if one cable end is left floating, you’d have a great 6 MHz antenna.

Both RADs and DRs use RS-485 communications transport with the highest common mode immunity parts available. This is required since the common mode voltage developed between a distant RAD in a grounded electrical box, and the HAL equipment rack ground must not damage the devices or interfere with data transmission. The shield helps in this typical situation because the shield contacts before the internal data and power conductors, safely reducing or eliminating the common mode voltage. Note that in technical grounding systems, isolating the RAD or DR from the electrical box is required by using nylon screws and a mud ring, for example.

From S&VC magazine, here’s more about shielded CAT 5 cables.

For the Ferrari of shielded connector approaches – and for those with nimble hands – check out the Sentinel Connector Systems shielded plugs at the bottom of this page.

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