DiSEqC (pronounced D-eye-seck) is the acronym for Digital Satellite Equipment Control, an open standard developed by EUTELSAT (European Telecommunications Satellite Organization) and the satellite industry. Designed primarily to address the problem of multi-satellite systems reception, DiSEqC is now an internationally acknowledged standard, allowing for efficient communication between satellite receivers and their external peripherals, including Low Noise Block converters (LNBs), Integrated Receiver/Descramblers (IRDs) and multi-switches. Deploying equipment with DiSEqC enables the delivery of multiple satellite feeds over a single coax cable, and eliminates the need to install numerous wires into a residence to receive multi-channel satellite.

Multiple Channels without DiSEqC

In satellite transmission, a multitude of channels is transmitted over the same bandwidth to enable the delivery of today's broadband content requirements. Satellite transmission squeezes more channels onto a frequency bandwidth by dividing the channels between vertical and horizontal polarization and by using multiple satellites. Traditionally, the receiver uses voltage as a guide to "see" either vertical or horizontal transmissions from a single dish. A typical system is illustrated below.

In the early days of multiple satellite reception, two Universal LNBs were used -- one 12-volt switch and one receiver. For one satellite receiver to control the two LNBs, two different cables ran from the receiver to the external switch near the antenna. One was an RG6/11 cable, while the other was a 2-core electrical cable. The switch used applied voltage to transfer from one port or LNB to the other. If zero volts were applied to the switch, it stayed at port 1. If 12 volts were applied, the switch changed to port two.

In newer systems, an integrated "dual" LNB was developed and the need for a 2-core electrical cable was eliminated. The switching voltage was passed over the coaxial cable feeding the LNB. Only the needed polarity, as indicated by the voltage, was present over the coax. However, because this system could not handle multiple satellite feeds, there was still a need to expand its switching capabilities.

Initially, a 22KHz-tone generator was added to the receivers. When the switch "heard" the 22KHz tone, it switched to the other LNB. This allowed the system to control up to four polarities: 13V only, 18V only, 13V with a 22KHz tone and 18V with a 22KHz tone.

The Advantage of DiSEqC

DiSEqC acts effectively as a traffic cop for the various satellites and satellite signals. It directs the right satellite signals to the right customers and creates an integrated multi-satellite network with efficient signal-switching capabilities.

Based on the digital expansion of the 22KHz signal, DiSEqC relies on a switching box that detects the 22KHz tone pulsing rapidly on and off. There are various levels of DiSEqC technology, but for the purpose of this article, we will discuss DiSEqC Level 1.2. DiSEqC 1.2 not only allows digital commands to control polarization, frequency band and satellite position, but it permits a motorized satellite system to be completely controlled and powered by a single cable.

By using a DiSEqC 1.2 system, a single switch and a single cable can control multiple LNBs, allowing for multiple channel delivery without additional wiring or equipment.

With the DiSEqC standard, messages are sent in sequences of short bursts of 22KHz tones and carried over the single coax cable from the receiver's LNB input port to the switch. Each message is made up of digital bytes consisting of eight bits. Each bit consumes a specific time, and the proportion of that time filled with the 22KHz burst determines whether the bit is a 1 or a 0 byte.

• The first byte allows for the listening devices (slaves) to synchronize to the signal and includes information about whether a response is required or if the message is a retransmission.
• The second byte indicates the message's intended destination device.
• The third byte is the command byte that tells the listening devices what to do. This is followed by a number of data bytes containing information necessary to carry out the command, such as the required angle of the polarizer.

One of the biggest advantages of DiSEqC is its backward compatibility. DiSEqC accessories can be integrated into older 13/18 volt and 22KHz systems. For example, two older universal LNBs can be connected behind a DiSEqC multiswitch, with communications between the receiver and the multiswitch made possible through DiSEqC commands.

Because DiSEqC provides for the delivery of multiple satellite channels over a single wire, and is backward compatible with existing equipment, it is a technology of the future that works with the technology of the past. It is ideal for the broadband provider that wants to deliver multiple video channels to the already-wired receiver efficiently and cost effectively. Today, DiSEqC is more widely used in Europe than it is in North America, but as satellite television becomes increasingly a part of the American consumer's entertainment budget, that is likely to change. The DiSEqC standard has been adopted by EchoStar in its line of IRDs.

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