Coax Cables

The BNC (Bayonet-Neill-Concelman) connector is the most commonly used coax connector. This large ”bayonet“ connector features a slotted outer conductor and an inner plastic dielectric, and it offers easy connection and disconnection. After insertion, the plug is turned, tightening the pins in the socket. It is widely used in video and Radio Frequency (RF) applications up to 2.4 GHz. It is also common in 10BASE2 Ethernet networks, on cable interconnections, network cards, and test equipment.

The TNC connector is a threaded version of the BNC connector. It works in frequencies up to 12 GHz. It‘s commonly used in cellular telephone RF/antenna applications.

The N connector is a larger, threaded connector that was designed in the 1940s for military systems operating at less than 5 GHz. In the 1960s, improvements raised performance to 12 GHz. The connector features an internal gasket and is hand tightened. It is common on 2.4-GHz antennas.

The UHF connector looks like a coarse-threaded, big center-conductor version of the N connector. It was developed in the 1930s. It is suitable for use up to 200–300 MHz and generally offers nonconstant impedance.

The F connector is most often used in cable and satellite TV and antenna applications; and it performs well at high frequencies. The connector has a 3/8–32 coupling thread. Some F connectors are also available in a screw-on style.

The SMA (Subminiature A) connector is one of the most common RF/microwave connectors. This small, threaded connector is used on small cables that won’t be connected and disconnected often. It’s designed for use to 12.4 GHz, but works well at 18, and sometimes even up to 24 GHz. This connector is often used in avionics, radar, and microwave communications.

The SMC (Subminiature C) connector is a small, screw-on version of the SMA. It uses a 10–32 threaded interface and can be used in frequencies up to 10 GHz. This connector is used primarily in microwave environments.

The SMB (Subminiature B) connector is a small version of the SMC connector. It was developed in the 1960s and features a snap-on coupling for fast connections. It features a self-centering outer spring and overlapping dielectric. It is rated from 2–4 GHZ, but can possibly work up to 10 GHz.

The MCX (Micro Coax) connector is a coax RF connector developed in the 1980s. It has a snap-on interface and uses the same inner contact and insulator as the SMB connector but is 30% smaller. It can be used in broadband applications up to 6 GHz.

Digital signal (DS) speeds are used to classify the capacities of lines and trunks as designated by the Trunk (T) carrier systems. The most well-known T carrier system is the North American T1 standard, which was originally designed to transmit digitized voice signals at 1.544 Mbps (DS-1). T carrier systems now carry digital data as well as voice transmissions.

DS-3 lines offer the functional equivalent of 28 T1 channels, operating at 44.736 Mbps (commonly rounded up to 45 Mbps). These lines handle up to 672 voice conversations and are used in high-speed interconnect and DS cross-connect (DSX) applications.

DS-4 offers 274.176 Mbps transmission—the same as 4032 standard voice channels—and has 168 times the capacity of T1. This performance level is generally used for carrier backbone networks.

Products offering DS-3 and DS-4 functionality comply with T3 and T4 standards, respectively, and with Bellcore GR-139-CORE specifications.

Depending on the environment and how the electrical signal is sent over the cable, coax can be used for three types of transmissions.

Baseband transmissions use the entire communication channel capacity to transmit a single data signal. Many LANs employ Thin coax for baseband signaling.

Broadband transmissions use different frequencies to carry several analog signals simultaneously. Each signal can for be a different type of information—data, voice, even video. Broadband transmissions over coax employ either one or two cables. With single-cable coax wiring, frequencies are split into individual channels for each station; some channels are allocated for bidirectional communication. Dual-cable coax wiring uses one cable for sending and one cable for receiving data, each with multiple channels. Broadband transmissions are ideal for long distances. Thick coax is often used for broadband transmissions.

Unlike broadband transmissions, carrierband transmissions can only use one information channel. Carrierband is best suited for the horizontal subsystems (subnetworks) in industrial settings. Many LANs use Thin coax for carrierband signaling.

The Ethernet standard supports 10-, 100-, and 1000-Mbps speeds. It supports both half- and full-duplex configurations over twisted-pair and fiber cable, as well as half-duplex over coax cable.

However, the Thick and ThinNet Ethernet standards support only 10-Mbps speeds.

Standard (Thick) Ethernet (10BASE5)
• Uses “Thick” coax cable with N-type connectors for a backbone and a transceiver cable with 15-pin connectors from the transceiver to the network interface card.
• The maximum number of segments is five, but only three can have computers attached. The others are for network extension.
• The maximum length of one segment is 500 meters.
• The maximum total length of all segments is 2500 meters.
• The maximum length of one transceiver cable is 50 meters.
• The minimum distance between transceivers is 2.5 meters.
• No more than 100 transceiver connections per segment are allowed. A repeater counts as a station for both segments.

Thin Ethernet (ThinNet) (10BASE2)
• Uses “Thin” coax cable (RG-58A/U or RG-58C/U).
• The maximum length of one segment is 185 meters.
• The maximum number of segments is five.
• The maximum total length of all segments is 925 meters.
• The minimum distance between T-connectors is 0.5 meters.
• No more than 30 connections per segment are allowed.
• T-connectors must be plugged directly into each device.