ethernet – Engineering Radio

Shielded Category Cable

There is some disagreement in the organization that I work with regarding the use of Shielded Cat 5e cable. Is it needed and if so, when and where? Category cables commonly used in Ethernet computer networks and also used for analog audio and other data applications come in a variety of flavors. Shielded (Shielded Twisted Pair or STP) and unshielded (Unshielded Twisted Pair or UTP) Cat 5, 5e, and 6 are the most common in radio broadcast facilities.

The main purpose for using UTP and STP for high-speed data transmission is common-mode rejection. Cables that are installed in office buildings are subject to various electric and electronic noise sources. Properly installed UTP works to reject these unwanted signals by using differential signaling, which is balanced. Differential signaling can best be described as transmitting information using two complementary signals that are opposite from one another.

Noise rejection, differential signaling. "DiffSignaling" by Linear77 - Own work. Licensed under CC BY 3.0 via Wikimedia — Noise rejection, differential signaling. “DiffSignaling” by Linear77 – Own work. Licensed under CC BY 3.0 via Wikimedia

The key performance measurement in category cable is Common Mode rejection. Outside noise will introduce a common mode signal on the cable which will be canceled out by the differential amplifier on the receiving end of the circuit. Proper terminations and good wiring techniques are very important for proper performance.

Using the correct patch panel termination, terminating block or RJ-45 (8P8C) connectors are required to maintain the advertised bandwidth of the cable. There is also a difference in the connector and terminating block designs for solid versus stranded cables. Using improper connectors for the type of cable installed can cause dropouts and loss of data.

When installing category cable, care must be taken not to kink the cable, not to exceed the recommended minimum bending radius, or exceed the maximum pulling force. Each of these will degrade the cable performance by changing the physical characteristics of the cable. Each pair of wires in category cable has a different twist. Altering these twist ratios by stretching the cable or bending it too sharply will increase the NEXT (Near End Cross Talk) and FEXT (far end cross talk) between pairs. In Gigabit networks, this will degrade throughput and create bottlenecks.

Generally speaking, the minimum bending radius is four times the cable diameter, or approximately one inch for Category 6 cable. The maximum pulling tension is not more than 25 ft/lbs or 110 Newtons.

In high EMF environments, shielded cable (STP) can be beneficial in mitigating high electrical noise along with the proper installation techniques noted above. Signaling levels on 100BaseT are +1, 0, and -1 volt (MLT-3 Encoding). On Gigabit Ethernet, the levels are +1, +0.5, 0, −0.5, and −1 Volt (PAM-5 Encoding). Induced voltages on cables from external sources can degrade network performance and create bottlenecks. High EMF environments would include places like transmitter sites and anything on a tower or rooftop. Properly terminated shielded cable is necessary for EMP protection from lightning strikes or other sources. STP has special shielded metal connectors which each category cable class. These connectors supply the path to the ground through the RJ-45 jack.

Ungrounded shields are useless.

RJ-45 or 8P8C shielded plug for Category 6 STP

There are also other cable characteristics to consider such as UV-resistant jacking for outdoor installations or gel-filled (AKA “flooded”) cable for wet locations. Fortunately, there are plenty of sources for these types of cables and they are not terribly expensive.

To answer the question at the beginning of the post; STP can be beneficial at high EMI/EMF or RF sites to mitigate induced voltages on the cable from external sources provided it is properly terminated. In office and studio locations that are not at or next to a transmitter site, UTP is more than adequate provided it is properly installed and terminated.

Fifth Generation WLAN

Like all data-carrying technology, WLAN, or WiFi, continues to evolve into a better, faster, and more robust platform. The IEEE wireless ethernet specification 802.11ac combines all of the past developments, plus some added features, into one specification. Here are some of the highlights:

Operation on 5 GHz only. Many more available channels in this spectrum than in 2.4 GHz
Increased channel bonding makes wider channels carry more data. In the 5 GHz spectrum channels are 20 MHz wide and do not overlap. 802.11ac allows for 40, 60, 80 or even 160 MHz channels. This is great for short distances, longer distances will be prone to greater interference over wider channels
Modulation schemes that allow up to 256 QAM. A 256 QAM constellation is going to look pretty crowded unless it is on a wide channel. Again, this would be good for short distances.
Increased MIMO. Up to 8×8 MIMO (Multi In Multi Out) which can greatly improve throughput. MIMO means multiple transmitters and antennas in the same unit. The first number is the transmitter count the second number is the antenna count. Thus an 8X8 system will have eight transmitters and eight antennas. This allowed beam forming by use of phased antenna arrays, which can greatly reduce multi-path
MU-MIMO (Multi-User MIMO). Basically, the access point sends the data frame only to the desired host, thus instead of acting like an ethernet hub sending the frame to every connected host, the AP is acting more like an ethernet switch.

The goal of all of these modifications is to get gigabit transfer rates over WLAN.

What does all of this have to do with radio broadcast, one might ask? That is a good question.

There are several applications that have to do with remote broadcasting. Many sports areas, nightclubs, or other likely places to be broadcasting from have WIFI installed. Using a laptop with an AoIP client installed not only can connect to the studio for audio delivery, but the same laptop can also use RDP or VNC to control the station’s automation computer as well. This means easier integration of the remote into voice-tracked or syndicated programming.

Secondly, wireless LAN bridges between the studio and the transmitter site can act as an STL, a backup STL, a remote control return link, a bridge for a network-connected transmitter, a VoIP phone link, IP security camera backhaul, or almost anything else that can send ethernet data. I have found it useful to simply have a computer available at the transmitter site, even if it is only to download manuals and whatnot. We have taken several old Windows XP machines and reloaded them with a Linux variant and installed them at various transmitter sites. It saves the trouble of having to download a manual on the smartphone and then page back and forth across a really small screen to read it. As for using unlicensed WiFi to link to a transmitter site; the link between the WICC studio and transmitter site runs 78 Mbps most days. This is a two-mile link over mostly water. I will say, when there is fog, the link rate drops to 32 Mbps, which is still pretty good, all things considered.

Of course, office network applications; laptops, tablets, smartphones and other personal devices.

Finally, Broadcast Engineers really need to keep abreast of networking technology. There are many, many applications for WiFi units in the broadcast industry.

Category 7 Cable

As data transfer technology progresses, so do cable types. Category 6 UTP copper cable is commonly used today in ethernet installations where 1000BaseT (or gigabit ethernet) systems are required. Cat 6 cable has a certified bandwidth of 250 MHz (500 MHz for Cat6a). Category 6 cable is a newer version of Category 5 and 5e cable wherein the wire pairs are bonded together and there is a separator to keep each pair of wires the same distance apart and in the same relationship to each other. The four twisted pairs in Cat 6 cable is also twisted within the overall cable jacket.

Category 7 cable is much different from its predecessors. It has an overall shield and individual pairs are shielded:

Shields on individual pairs are required to reduce cross-talk (FEXT, NEXT). It also requires special shielded connectors called GG45 plugs and jacks. Pinouts and color codes are the same as gigabit ethernet (Category 5e and 6) however, Category 7 (ISO 11801 Class F) jacks and plugs also have to contact the corners of the connector or jack. This allows better shielding. A small switch in the jack senses when a Category 7 type connector is inserted and switches to the corner contacts, thus keeping jacks and patch panels backward compatible with Category 5/6 cables.

Category 7 GG45 connectors, jack and plug

Category 7 cable is rated for 600 MHz bandwidth (1000 MHz for 7a) which translates to 10 GB ethernet. This was previously the domain of fiber cable. Copper cable has some advantages over fiber; lower propagation delays require less complicated equipment, copper is less expensive than fiber and more durable. It is nice to have the flexibility to use copper cable on 10 GB ethernet for runs of 100 meters or less. Longer runs still require fiber.

Category 7 and 7a cable looks remarkably similar to the older Belden multipair “computer cable” pressed into service as audio trunk cable seen so often in older studio installations.

Pinouts

Over the years, I have collected many pinouts for all sorts of interfaces, connectors, jacks, etc. These are all stored on my laptop and on my smartphone. It is easy enough to look these things up online, however, there are occasions when the internet is not available for whatever reason. Thus, this is my collection of pinouts, many of which have been adapted from Wikipedia articles. Many times I put things here for my own use. However, if I have spent ten minutes looking for the USB pin out on my smartphone, someone else has done the same thing. Most of these images have higher resolutions available.

Enjoy!

EIA/TIA 568a and b ethernet cable standard

Standard networking connectors for Ethernet connections. Rumor has it that only the “A” standard is accepted for government work and the “B” standard is being depreciated.

803.3af Power over Ethernet, imposed on EIA/TIA 568 a and b

Power over Ethernet pinouts. More and more commonly used in VOIP phone systems, but can also be found in wireless access points and other things of that nature.

10/100 base T cross over cable — 10/100 base T cross-over cable

Ethernet crossover cables are useful for connecting to similar pieces of equipment together, e.g. a computer to a computer, or a switch to a switch. Many new switches have port sensing, which will automatically cross the connection if a straight through cable is used. Others have a specific port or a switch for a specific port which will cross over the cable. Gigabit Ethernet uses all four pairs, thus a 1000 base T crossover looks a little bit different.

10/100/1000 base T Ethernet crossover cable

This type cable is backwards compatible with 10/100 base T systems.

Telephone system equipment jacks.

Registered Jack (RJ) 48, commonly used on T-1 and ISDN circuits

RJ48 and 48X used on T-1 (DS-1) and ISDN connections. Since BRI and PRI ISDN are two wire circuits, the active pins are 4/5, which is the same as an RJ11. I have often used RJ11 jacks for ISDN and found no issues with doing so.

Crossover cable for T-1 (DS-1 or DSX-1 interface). Note, this is different from an Ethernet crossover cable, which will not work for in a DS-1 interface. A T-1 loopback connector goes from pin 1 to pin 4 and pin 2 to pin 5 on a 8P8C connector.

RJ21 and 21X connectors are often found on the side of punch blocks and make for quick connections on cabling trunks.

The generic 25 pair color code, which is always a good thing to have.

RS-232 data pins out for various connectors

RS-232 is still commonly used for data transfer in broadcast facilities. RS-485 is also used, however, that standard is often used with screw terminals or some other generic connection.

Null modems for connecting equipment together and testing.

Universal Serial Buss (USB) connections and pinouts

Various USB connectors and pinouts. USB has replaced RS-232 data ports on most newer computers.

Computer graphics card pinouts.

Computer parallel port pinout, not used very much anymore, replace by mostly USB devices. Can also be used as a limited GPI/GPO interface. Some small automation software programs use pins 10,11,12,13 and 15 for closure information and pins 1, 14, 16, and 17 for output switching, machine starts and the like.

PS2 mouse and keyboard connectors, again, replaced by USB but still found on older motherboards.

RJ-45 to balanced analog and digital audio

RJ-45 to balanced audio. This is a fairly standardized audio application for RJ-45 connectors developed by Radio Systems/Studio Hub. It is also used by Telos/Axia and Wheatstone, although often the +/- 15 VDC power is not included.

XLR connectors, old technology, still used

The ubiquitous XLR connector, still used for analog audio and also AES/EBU digital audio.