Round Trip Time, or RTT, refers to the amount of time it takes for a signal to travel from a particular terrestrial system to a designated satellite and back to its source. Round Trip Time is also referred to as Round Trip Delay.
There are several factors that affect Round Trip Time. Generally, the speed of light limits Round Trip Time. The type of satellites used also affect Round Trip Time. Geostationary satellites have the longest Round Trip Time when transferring signals. On the other hand, Low Earth Orbit (LEO) satellites have the shortest Round Trip Time.
The concept of Round Trip Time is also applied in data transfers between computers. In this context, Round Trip Time is the amount of time required by a computer to send data packets to a remote computer and back again to the original source. Several factors affect the Round Trip Time for computers. These include the data transfer rate of the Internet connection of the source computer, the physical distance between the source and the destination, the amount of traffic currently present on the local area network, and the number of nodes or computers between the source and destination.
In both cases, Round Trip Time can range from a few seconds to a few milliseconds. The better the transfer rate and the nearer the two units, the faster the Round Trip Time. Also, Round Trip Time incorporates a theoretical minimum which comes from the premise that it can never be lower than the time the signals or data require to propagate within the transmission media.
A satellite finder is a specialized device that has a signal reader to point satellite dishes to the direction where there is good signal strength. In conjunction with satellite dishes, LNB’s or Low Noise Blocks also make use of satellite finders.
Satellite finders are of two major types:
- Analog satellite finders determine the strength of the signal that the satellite dish is receiving. It will then display on its screen the signal strength. An individual can use this device first by pointing the satellite dish to a location where he thinks the satellite is situated. He then has to read the analog satellite finder. If the device displays low signal strength, he can adjust the satellite dish to get better signal. Analog satellite finders are generally inexpensive as they have a compact set of features.
- Digital satellite finders are a more intricate type of device for locating high signal strength. These satellite finders have been pre-programmed with information regarding the exact locations of satellites. Through the digital satellite finder, a user not only can determine that he has found a satellite, but he can also know which satellite he has found. Digital satellite finders are more expensive than analog satellite finders mainly due to the information the former contains.
Certain satellite finders are now incorporated in a number of advanced devices. Newer models of mobile phones and other handheld pieces of hardware have satellite finders that enable users to find the best signal strength while on the move. There are also satellite finding software which users can install on their computers. These applications rely on information provided by telecommunications and broadcast networks.
The Ku (Kurtz-under) band is part of the electromagnetic spectrum’s microwave range of frequencies. In applications such as radar, the band covers the scope of 12 to 18 GHz according to IEEE standards’ frequency band nomenclature.
Satellite communications uses Ku bands, specifically for broadcasting and editing satellite TV. Multiple segments divide this band further split into geographical areas as identified by the International Telecommunications Union (ITU).
The Ku band’s range of frequencies covers 11.7-12.7 GHz for downlink frequencies and 14-14.5 GHz for uplink frequencies.
Digital Video Broadcasting (DVB) is the most popular Ku band format for digital reception, competing with the Digicipher II format.
The National Broadcasting Company (NBC) was the first commercial TV network to extensively use the Ku band in most affiliate feeds back in 1983.
ITU Region 2 sectors encompassing the larger part of North and South America cover 11.7 to 12.2 GHz, currently orbited by more than 21 Fixed Satellite Service (FSS) Ku band satellites.
Each sector needs a 0.8-1.5 meter antenna and uses 12-24 transponders which consume 20-120 watts per transponder for clarity of reception.
Broadcasting Satellite Service (BSS) takes the 12.2-12.7 GHz sector of the Ku band. These direct-broadcast satellites usually have 16-32 transponders.
Each transponder offers a bandwidth of 27 MHz while using up 100-240 watts per device, with receiver antennae as small as 18 inches (450 mm) .
ITU Region 2 sectors of the Ku band correspond to Europe and Africa (with 11.45-11.7 GHz and 12.5-12.75 GHz band ranges, respectively) reserved for the FSS, with an uplink frequency range of 14.0-14.5 GHz.
Direct Broadcast Satellite (DBS) dishes use a low-noise block converter with an integrated feedhorn (LNBF). Often times, small diplexers allocate the resulting intermediate frequency signal in the same cable television wire that transmits lower-frequency signal from a terrestrial antenna. A separate diplexer then divides the signals to the integrated receiver-decoder (IDS) of the DBS set-top box and to the receiver of the TV set.
Up-to-date Ka band systems use more intermediate frequency blocks from the LNBF. One of these intermediate frequency blocks will cause disruption to UHF and cable TV frequencies that are more than 250MHz, ruling out the use of the diplexers. The other block is superior to the original with frequencies up to 2.5 GHz. This would oblige connection of the LNB to first-class all-copper RG-6/U cables. This would also add up to the higher electrical current and electrical power requirements for multiple dual band LNBFs.
For some free-to-air (FTA) and satellite Internet, seasoned individuals recommend a universal LNB. Majority of the DBS signals in North America use circular polarization, rather than linear polarization. This uses a different type of LNB for suitable reception. With this, the polarization must attune to the counterclockwise and clockwise directions, instead of the vertical and horizontal.
In the case of DBS, the voltage provided by the set-top box to the LNB establishes the setting of the polarization. In multi-TV systems, a dual LNB enables both to function at once using a switch that serves as the distribution amplifier. The amplifier then transmits the proper signal to each box in accordance to the selected voltage. The most recent systems may choose polarization and which LNBF to utilize by transmitting DiSEqC codes. The earliest satellite systems power-drove a rotating antenna on the feedhorn, during the time when there was only one LNA or LNB on a very large TVRO dish.
One of the problems encountered by people using LNB is loss of signal due to moisture accumulation, especially during inclement weather. During snowy or rainy conditions, the snow or rain collecting on the LNB tends to interrupt the signal. Wiping off the moisture from the LNB will cause the signal to return. Some would even tie a plastic bag around the device just to keep moisture away.
An LNBF with appropriately constructed shield over the device can eliminate the problem with moisture accumulation and signal loss. This protects the device from precipitation while not obstructing signal reception.
The Ka band is an electromagnetic frequency range which covers 26.5 – 40 GHz. The Ka band is a portion of the K microwave band, which ranges from around 18 to 40 GHz. ‘Ka’ is short for ‘K-above,’ denoting that this range approximately covers the upper third of the entire K band. The term ‘Ka’ frequently refers to the band with the recommended operating frequency of the WR-28 waveguide (within 26.5 – 40 GHz) .
The IEEE K band is segmented into three secondary bands:
- Ka (K-above) band – ranging from 26.5–40 GHZ, which is primarily used in experimental communications and radar
- K band – ranging from 18–27 GHz
- Ku (K-under) band – ranging from 12–18 GHz, mainly for radar, satellite communications, and terrestrial microwave transmissions
Downlink within the 18.3–18.8 or 19.7–20.2 GHz bands, communications satellites, and high-resolution close-range targeting radar (aboard military aircraft) use the 30/20 GHz band. The uplink for the 30/20 systems are around 30 GHz. This radar range is used for vehicle speed identification required by law enforcement.
The Ka band uplink frequencies are within 27.5–31 GHz, while the downlink frequencies are within 18.3–18.8 and 19.7–20.2 GHz.
Ka band satellites usually transmit using more power than C band satellites, although C band dishes are bigger than Ka band satellites. Ka band dishes range from 2 feet to 5 feet in diameter, while C band dishes range from 7 feet to 12 feet.
C band dishes are also known as BUDs (Big Ugly Dishes) due to their relative size. Conversely, due to the higher frequency range and smaller dish size, the signals are more prone to signal disruptions and quality problems caused by adverse weather conditions such as rainfall (recognized as rainfade).
Free satellite is a service that enables users to have numerous digital TV channels, including a number of high definition programs. It allows viewers to have access to high definition and free-to-air digital television. Free satellite also lets users have access to more radio stations. This service is gaining much popularity in the UK and some other countries.
How can one acquire this service? After contacting a company that provides a free satellite service, a user needs to pay for hardware such as a dish and a set-top box. The price of a set-top box ranges from around 60 dollars to well over a hundred dollars. This depends on the box’s support for high definition programming.
The user also needs to pay for the installation of the said equipment. A professional from the company will carry out the installation. The cost of free satellite installation including the dish is around a hundred dollars. Once the pieces of hardware have been set up, the user can enjoy the channels provided by the satellite service without paying a monthly subscription. Hence, it is termed “free satellite”.
Free satellite uses advanced technology to provide more channels. Companies that offer this service make use of a specialized type of receiver, card, and dish. These pieces of hardware have a lower tendency to fail, which results to continuous viewing.
Individuals who wish to acquire this service need information to enable them to choose the best free satellite service. They can visit establishments and public areas where a television set uses a certain free satellite service and look at the quality of the images. One can contact the company that provides the service if he finds the satellite service appropriate.
LNB stands for low-noise block converter. This is the downlink antenna of a parabolic satellite dish. When two LNBs are in one dish, this becomes a dual band LNB. The LNB may be designed as a feedhorn, that is, an open-ended waveguide constructed with an increasing cross-sectional area. The waveguide is a structure intended to guide electromagnetic and sound waves towards a desired direction.
A dual band LNB with an integrated feedhorn has a pair of low noise blocks attached to the waveguide output probes that are used to down-convert the arriving moderated carrier Ku and C band signal to moderated intermediate frequency signals. In addition, a dual band LNB also has a Ku band waveguide set up on the clamp for changing of focus, a clamp for a Ku band waveguide, and a housing that rotates for a C band coaxial waveguide.
A servomechanism, a device set into motion by another mechanism but which assists that other mechanism’s operation, thrusts the support member to place the energy output coupling probes of the waveguides. This is to suit the polarization of the inward RF energy. This significantly reduces insertion loss and eliminates the need for polarizers. The minimized insertion loss allows defocusing of the Ku band waveguide to broaden the beam width to perk up accuracy without reducing the expansion and degrading performance.
Attached to the outer surface of the housing is a pair of power modules and a position adjustable scalar. The power modules have voltage regulators and transient suppressors attached to the pair of LNB. These block out incoming transients and modify the incoming dc voltage while producing the moderated intermediate frequency carrier signals. Hence, the heat produced by the power modules is set away from the low noise blocks, ensuring an increased life and a better operating performance.
The features specifications of a dual LNB are as follows:
- Conversion gain: 58dB (min.)
- DC current consumption: 90mA (max.)
- Input frequency range:
Output frequency range:
- Low band: 10.7~11.7GHz
- High band: 11.7~12.75GHz
L.O. frequency: 9.75/10.6gHz±1MHz (max.) 25°C
L.O. frequency stability: 9.75/10.6GHz ± 2MHz (max.) at -40~+60°C
Output connector type: 75Ω female connector
Output VSWR: 2.0:1 (typical)
- Low band: 950~1,950GHz
- High band: 1,100~2,150GHz
Dual LNB with multi-switch for terrestrial television
One dual LNB comes with a multi-switch, enabling dc voltage from the satellite receiver to pass through the terrestrial antenna input without resulting to an alteration or interference of the signal strength of the satellite and the outdoor antenna pictures. By incorporating an external dc block adapter with the LNB, the multi-switch can be used with improved and unimproved antennas without requiring external power injector.
C Band is a label for particular segments of the electromagnetic spectrum. It also refers to a range of light wavelengths used in the communications field. The IEEE (Institute for Electrical and Electronics Engineers) C band and its variants are the ranges used in some satellite television transmissions, some cordless home phones, Wi-Fi devices, and weather radars. The lower C band frequencies suit best with harsh weather conditions (than Ku or Ka band frequencies) for satellite communications.
The C band uses the 5.925-6.425 GHz range for uplink and 3.7-4.2 GHz range for downlink. Large satellite dishes require the C band. Dishes for this frequency band are usually between 6 to 9 feet across with varying signal strength.
IEEE C Band
The microwave frequency range of the electromagnetic spectrum from 4 GHz to 8 GHz refers the IEEE C band.
The IEEE C band was the first band allotted ground-to-satellite commercial communications. Open-satellite communications use C-band for round-the-clock satellite television networks or raw feeds. This employment differs from Direct Broadcast Satellite (DBS), a closed system that delivers subscription programming sent to small dishes linked to receiving equipment.
C band is usually associated with Television Receive-Only (TVRO) satellite systems. These ‘big dish’ systems are optimal for the C band, as opposed to small receiver antennae.
C band dishes are much larger than other band dishes, and sometimes referred to as BUDs (Big Ugly Dishes). Most antennae for C-band compatible systems are within the range of 7.5-12 feet for commercial satellite dishes.
The NATO C Band
The segment of the electromagnetic spectrum from 500 MHz to 100 MHz is known as the NATO C band.
The 5.4 GHz band used for IEEE 802.11a Wi-Fi and wireless home phone devices occasionally lead to interference with weather radar working within the C band.
PSK, or Phase Shift Keying, refers to a specific form of phase modulation. Phase shift keying is done through the use of a distinct number of states. On the other hand, phase modulation is a form of frequency modulation where the phase of the carrier wave is modulated to accept and encode digital information. Modulation takes place during each phase change.
QPSK, which stands for Quadrature Phase Shift Keying, refers to a type of phase modulation algorithm where there are four states involved. These four states also refer to four phases wherein a particular carrier is sent to QPSK. These states consist of 45, 135, 225, and 315 degrees.
QPSK is an algorithm providing procedures used in calculating and finding a specific value. With regards to its encoding, QPSK is capable of processing two bits for each symbol. This is due to the fact that QPSK has four possible states.
Compared to other phase modulation algorithms, QPSK has a higher tolerance level for link degradation. QPSK generally has a lower tendency of causing system failure. However, QPSK normally provides less data capacity than other types of algorithms.
QPSK is applied extensively on certain systems. It can be used to maintain the data rate while ensuring that the bandwidth of the signal is stable. This enables the system to efficiently utilize its bandwidth resources.
In addition, QPSK is implemented in transmitters and receivers used by particular communication systems. Wireless LAN standards also make use of QPSK in setting their structures. Likewise, certain Bluetooth technologies also apply QPSK in sending and receiving data.
Digital Satellite Equipment Control (DiSEqC) is a communication protocol standard used to connect satellite receivers to devices like an antenna rotor from a small dish or a multi-dish switch. DiSEqC allows more channels within a specific frequency bandwidth by transmitting channels with horizontal or vertical polarization.
Eutelsat, a European satellite service provider, developed DiSEqC and is now the protocol’s standard agency.
DiSEqC uses coaxial cables to transmit bi-directional information, two-way signals, and power. It is mainly used to manage motors and switches.
DiSEqC messages are transmitted in a series of rapid bursts (22KHz tone) adjusted by the coax cable power supply from the input on the receiver. Messages are digital bytes comprised of eight bits.
- DiSEqC 1.0 – allows switching among a maximum of 4 satellite sources;
- DiSEqC 1.1 – allows switching among a maximum of 16 satellite sources;
- DiSEqC 1.2 – allows switching among a maximum of 16 satellite sources, and controls a horizontally panning satellite motor;
- DiSEqC 2.0 – adds bi-directional communication to DiSEqC 1.0;
- DiSEqC 2.1 – adds bi-directional communication to DiSEqC 1.1; and
- DiSEqC 2.2 – adds bi-directional communication to DiSEqC 1.2
The system was apparently created by Eutelsat to allow Continental European users to shuttle between the SES Astra 1 satellite block and Eutelsat’s HotBird system. Majority of Europe’s satellite receivers now support DiSEqC version 1.0 upwards. All receivers supporting Eutelsat’s standard are now certified to use the DiSEqc logo indicating the version that they support.
DiSEqC 1.3 and 2.3 are often used by retailers and manufacturers to identify DiSEqC used with other protocols. Eutelsat, however, does not authorize such terminology.
A transponder is a wireless device that transmits and receives electrical signals. The word “transponder” is derived from two words: “transponder” and “transmitter”. In telecommunications, the term is abbreviated as XPDR, XPNDR, TPDR, or TP.
A transponder is an automatic device, which acts as a signal receiver, amplifier, and re-transmitter. It is also defined as an automatic device that transmits an encoded message in resoponse to another encoded received signal. A transponder is also considered as a receiver-transmitter generating a signal in response to electronic interrogation.
Transponders were initially created to locate objects, and they are still used for the same purpose at present. World War II saw the initial use of transponders aboard aircrafts to identify whether the craft was “friend” or “foe”. Sending the correct encoded messages in response to predetermined interrogation frequencies would help radar operators to identify pilots.
A transponder operates by receiving an interrogator signal (which “asks” for information) and then transmits a radio wave at an encoded frequency. A built-in frequency converter broadcasts a signal on a frequency other than the one previously transmitted on. The transponder and interrogator signals are identified simultaneously because of the different receiving and transmitting frequencies.
Transponders can also measure distance by formulating the time elapsed from sending the interrogator signal and receiving of the transponder signal.
Transponder technology is now widespread. Highways utilizing electronic toll systems using this technology can automatically compute the toll to be paid. Some cars are equipped with these devices, which help locate the vehicle in cases of emergency.
Mobile or cellular phones have a more compact version of the transponder chip on board. Televisions also employ the use of this device. Ground-based satellite transmitters send compressed digital audio/video to a transponder in their orbiting satellites, and the local stations receive and broadcast the programs to a landlocked dish.
8PSK, or 8 Phase Shift Keying, is a modulation method. It generally involves variations within a specific waveform so the said signal can produce data.
In 8PSK, the modulation of data is carried out to the bits directly from the output produced by the physical channel mapping procedure.
Since 8PSK is considered a phase modulation algorithm, this technique can be used to calculate certain waveform measures and find a particular value.
8PSK is an extension of QPSK. The main difference between the two is that the former uses 8 states whereas the latter uses 4. Another type of PSK related to 8PSK is 16PSK which, as its name suggests, uses 16 states.
Given the above characteristics, 8PSK tends to slightly use more DSP (Digital Signal Processor) cycles than other PSKs. Nevertheless, 8PSK is capable of transferring a greater amount of data with the same bandwidth.
In contrast to the other types of PSKs which can process only two bits per symbol, 8PSK can process 3 bits per symbol. This is made possible by 8PSK’s eight states. In addition, 8PSK has a less amount of tolerance to link degradation than other PSKs.
8PSK is used in a number of technologies. Antennas of devices such as radios and other telecommunication system hardwares are created using the 8PSK modulation technique. New models of modems also make use of 8PSK. It allows the said type of hardware to send and receive more data in less time. Aside from these, wireless LAN systems also use of 8PSK devices.