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Sebuah antena penerima satelit 2,5m untuk akses internet melalui satelit dua arah.

VSAT adalah singkatan dari Very Small Aperture Terminal adalah stasiun penerima sinyal dari satelit dengan antena penerima berbentuk piringan dengan diameter kurang dari tiga meter. Fungsi utama dari VSAT adalah untuk menerima dan mengirim data ke satelit. Satelit berfungsi sebagai penerus sinyal untuk dikirimkan ke titik lainnya di atas bumi. Sebenarnya piringan VSAT tersebut menghadap ke sebuah satelit geostasioner. Satelit geostasioner berarti satelit tersebut selalu berada di tempat yang sama sejalan dengan perputaran bumi pada sumbunya. Satelit geostasioner mengorbit selalu pada titik yang sama di atas permukaan bumi, maka dia akan selalu berada di atas sana dan mengikuti perputaran bumi pada sumbunya.

Daftar isi

[sembunyikan] 1 Mengirim Dan Menerima Data 2 Perangkat

3 Komponen

4 Kedudukan Satelit

5 Keunggulan dan kekurangan

[sunting] Mengirim Dan Menerima Data

Mendapatkan data Internet dari setelit sama saja dengan mendapatkan sinyal televisi dari satelit. Data dikirimkan oleh satelit dan diterima oleh decoder pada sisi pelanggan. Data yang diterima dan yang hendak dikirimkan melalui VSAT harus di-encode dan di-decode oleh encoder dan decoder terlebih dahulu. Satelit Telkom-1 menggunakan C-Band (4-6 GHz). Selain C-Band ada juga Ku-Band. Namun C-Band lebih tahan terhadap cuaca dibandingkan dengan KU-Band. Satelit ini menggunakan frekuensi yang berbeda antara menerima dan mengirim data. Intinya, frekuensi yang tinggi digunakan untuk uplink (5,925 sampai 6,425 GHz), frekuensi yang lebih rendah digunakan untuk downlink (3,7 sampai 4.2 GHz).

Sistem ini mengadopsi teknologi TDM dan TDMA. Umumnya konfigurasi VSAT adalah seperti bintang. Piringan yang ditengah disebut hub dan melayani banyak piringan lainnya yang berlokasi di tempat yang jauh. Hub berkomunikasi dengan piringan lainnya menggunakan kanal TDM dan diterima oleh semua piringan lainnya. Piringan lainnya mengirimkan data ke hub menggunakan kanal TDMA. Dengan cara ini diharapkan dapat memberikan koneksi yang baik untuk hubungan data, suara dan fax. Semua lalu lintas data harus melalui hub ini, bahkan jika suatu piringan lain hendak berhubungan dengan piringan lainnya. Hub ini mengatur semua rute data pada jaringan VSAT.

Frame TDM selalu berukuran 5.760 byte. Setiap frame memiliki 240 sub-frame. Setiap sub-frame adalah 24 byte. Panjang waktu frame tergantung pada data rate outbound yang dipilih. TDMA selalu pada 180 ms. TDMA disinkronisasi untuk memastikan bahwa kiriman data yang berasal dari stasiun yang berbeda tidak bertabrakan satu dengan yang lainnya.

Pendapat umum mengatakan bahwa koneksi dengan satelit adalah koneksi yang paling cepat. Kenyataanya adalah tidak. Waktu yang dibutuhkan dari satu titik di atas bumi ke titik lainnya melalui satelit adalah sekitar 700 milisecond, sementara leased line hanya butuh waktu sekitar 40 milisecond. Hal ini disebabkan oleh jarak yang harus ditempuh oleh data yaitu dari bumi ke satelit dan kembali ke bumi. Satelit geostasioner sendiri berketinggian sekitar 36.000 kilometer di atas permukaan bumi.

[sunting] Perangkat

Terminal Antena Sangat Kecil adalah alat di stasiun bumi dan digunakan untuk mengirim serta menerima pancaran frekwensi daripada satelit. Antena VSAT berukuran lebih kurang 2 hingga 10 kaki (0.55-12 m) dipasang di atap ,dinding atau atas tanah dan pemilihan besar kecilnya antena sangat tergantung pada jenis frekuensi (misalnya C band atau Ku band) yang akan digunakan.

[sunting] Komponen

Komponen VSAT, terdiri dari:

.Unit Luar (Outdoor Unit (ODU)): 1. Antena/dish/parabola ukuran 2 hingga 4 kaki (0.55-2.4 m), yang dipasang pada

atap, dinding atau di tanah.

2. BUC (Block Up Converter), yang menghantarkan sinyal informasi ke satelit.Juga sering disebut sebagai Transmitter (Tx).

3. LNB (Low Noise Block Up), yang menerima sinyal informasi dari satelit. Juga sering disebut sebagai Receiver (Rx).

Unit Dalaman (Indoor Unit (IDU)):

1. Modem (Modulator / Demodulator), sebuah alat dipanggil Return Channel Satellite Terminal yang menyambungkan dari unit luar dengan IFL kabel berukuran panjang tidak lebih 50 meter.

2. IFL (Inter Facility Link). Merupakan media penghubung antara ODU & IDU. Fisiknya biasanya berupa kabel dengan jenis koaksial dan biasanya menggunakan konektor jenis BNC (Bayonet Neill-Concelman).

Satelit

1. Merupakan alat di orbit bumi khusus untuk menerima/ menghantar maklumat secara nirkabel, berkomunikasi melalui frekuensi radio.

menggunakan Satelit Telkom 2 (Indonesia) digunakan untuk Depdagri, dengan teknologi C band yang lebih tahan dengan cuaca di Indonesia (berhubungan dengan masalah curah hujan yang cukup tinggi di Indonesia). Menggunakan Komunikasi 2 arah, menerima dan menghantar isyarat. Daerah yang dipasang VSAT dikenali sebagai remote terminal, dikawal oleh hub station. Semua isyarat dari satelit dikirim ke hub terlebih dahulu sebelum dikirim kembali ke terminal remote lain, yaitu Propinsi / Kabupaten.

Kapasitas muat turun (download) ialah 1 Mbps tetapi boleh dinaiktaraf sehinga mencapai 45 Mbps**

Kapasitas muat naik (upload) pula ialah 128 Kbps tetapi boleh dinaiktaraf sehinga mencapai 1.1 Mbps**

Kontrak perjanjian SchoolNet hanya 1 Mbps muatturun dan 128 Kbps muatnaik

[sunting] Kedudukan Satelit

Jenis-jenis satelit bergantung kepada kedudukannya dengan permukaan bumi.

Ada 4 jenis satelit :

GEO -Geostationary (geo-synchronous) earth orbit MEO -Medium earth orbit

LEO - Low earth orbit

HEO -Highly elliptical orbit

[sunting] Keunggulan dan kekurangan

Keunggulan VSAT:

Pemasangannya cepat. Jangkauan terjauh dapat mencapai setengah permukaan bumi.

Kekurangan VSAT:

Koneksinya rentan terhadap gangguan cuaca (terhadap molekul air). Memakan tempat, terutama untuk piringannya.

Ku bandFrom Wikipedia, the free encyclopedia

Jump to: navigation, search

The Ku band (pronounced "kay-yoo") is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to "K-under" (in the original German, "Kurz-unten", with the same meaning)—in other words, the band directly below the K-band. In radar applications, it ranges from 12 to 18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521-2002. [1][2]

ITU Radio Band Numbers 4 5 6 7 8 9 10 11 12

ITU Radio Band Symbols VLF LF MF HF VHF UHF SHF EHF

NATO Radio bands A B C D E F G H I J K L M

IEEE Radar bands

HF VHF UHF L S C X Ku K Ka V W

edit

Ku band is primarily used for satellite communications, most notably NASA's Tracking Data Relay Satellite used for both space shuttle and ISS communications. Ku band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting. The band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU). NBC was the first television network to uplink a majority of its affiliate feeds via Ku band in 1983.

Contents

[hide] 1 Segments and regions

o 1.1 The Americas

o 1.2 Europe and Africa

o 1.3 Australia

o 1.4 Others

o 1.5 Indonesia

2 Advantages

3 Disadvantages

4 References

5 External links

[edit] Segments and regions

[edit] The Americas

Segments in most of the Americas are represented by (ITU Region 2) and they are, the 11.7 to 12.2 GHz (Local Oscillator Frequency (LOF) 10.750 GHz) band is allocated to the FSS (fixed service satellite, uplink 14.0 to 14.5 GHz). There are more than 22 FSS Ku-band satellites orbiting over North America, each carrying 12 to 24 transponders, 20 to 120 watts per transponder, and requiring a 0.8-m to 1.5-m antenna for clear reception.

The 12.2 to 12.7 GHz (LOF 11.250 GHz) segment is allocated to the BSS (broadcasting satellite service). BSS/DBS direct broadcast satellites normally carry 16 to 32 transponders of 27 MHz bandwidth running at 100 to 240 watts of power, allowing the use of receiver antennas as small as 18 inches (450 mm).

[edit] Europe and Africa

Segments in those regions are represented by ITU Region 1 and they are, the 11.45 to 11.7 and 12.5 to 12.75 GHz bands are allocated to the FSS (fixed satellite service, uplink 14.0 to 14.5 GHz).

In Europe Ku band is used from 10.7 to 12.75 GHz (LOF Low 9.750 GHz, LOF High 10.600 GHz) for direct broadcast satellite services such as those carried by the Astra satellites.

The 11.7 to 12.5 GHz segment is allocated to the BSS (broadcasting satellite service).

[edit] Australia

Australia is part of ITU Region 3 and the Australian regulatory environment provides a class license that covers downlinking from 12.25 GHz to 12.75 GHz and uplinking from 14.0 GHz to 14.5 GHz.

[edit] Others

Other ITU allocations have been made within the Ku band to the fixed service (microwave towers), radio astronomy service, space research service, mobile service, mobile satellite service, radiolocation service (radar), amateur radio service, and radionavigation. However, not all of these services are actually operating in this band and others are only minor users.

[edit] Indonesia

The ITU has categorized Indonesia as Region P, countries with very high rain precipitation. This statement has made many people unsure about using Ku-band (11 – 18 GHz) in Indonesia. If frequencies higher than 10 GHz are used in a heavy rain area, a decrease in communication availability results. This problem can be solved by using an appropriate link budget when designing the wireless communication link. Higher power can overcome the loss to rain fade.

Measurements of rain attenuation in Indonesia have been done for satellite communication links in Padang, Cibinong, Surabaya and Bandung. The DAH Model for rain attenuation prediction is valid for Indonesia, in addition to the ITU model. The DAH model has become an ITU recommendation since 2001 (Recommendation No. ITU-R P.618-7). This model can create a 99.7% available link so that Ku-band can be applied in Indonesia.

The use of the Ku-band for satellite communications in tropical regions like Indonesia is becoming more frequent. Several satellites above Indonesia have Ku-band transponders, and even Ka-band transponders. Newskies (NSS 6), launched in December 2002 and positioned at 95° East, contains only Ku-band transponders with a footprint on Indonesia (Sumatra, Java, Borneo, Celebes, Bali, Nusa Tenggara, Moluccas). The iPSTAR satellite, launched in 2004 also uses Ku band footprints. Measat has named the Ku-band footprint directed towards Indonesia Ku-band for Indonesi. Measat 4 plans to cover the whole of Indonesia from West to East. This satellite will be launched by Malaysia in 2007.

[edit] Advantages

Compared with C-band, Ku band is not similarly restricted in power to avoid interference with terrestrial microwave systems, and the power of its uplinks and downlinks can be increased. This higher power also translates into smaller receiving dishes and points out a generalization between a satellite’s transmission and a dish’s size. As the power increases, the dish’s size can decrease.[3]

The Ku band also offers a user more flexibility. A dish smaller size and a Ku band system’s freedom from terrestrial operations simplifies finding a suitable dish site. Ku band is generally cheaper and enables smaller antennas (both because of the higher frequency and a more focused beam).[4] Kuband is also less vulnerable to rain fade than the Ka-band frequency spectrum.

[edit] Disadvantages

There are, however, some disadvantages of Ku band system. Especially at frequencies higher than 10 GHz in heavy rain fall areas, a noticeable degradation occurs, due to the problems caused by and proportional to the amount of rainfall (commonly known as "rain fade").[5] This problem can be mitigated, however, by deploying an appropriate link budget strategy when designing the satellite network, and allocating a higher power consumption to reduce rain fade

loss. The Ku band is not only used for television transmission, which some sources imply, but also very much for digital data transmission via satellites, and for voice/audio transmissions.

The higher frequency spectrum of the Ku band is particularly susceptible to signal degradation, considerably more so than C-band satellite frequency spectrum. A similar phenomenon, called "snow fade" (where snow or ice accumulation significantly alters the focal point of a dish) can also occur during winter precipitation. Also, the Kuband satellites typically require considerably more power to transmit than the C-band satellites. Under both "rain fade" and "snow fade" conditions, Ka and Ku band losses can be marginally (but significantly) reduced using super-hydrophobic Lotus effect coatings.

[show] v • d • e

Wireless video and data distribution methods

[edit] References

1. ̂ IEEE Std 521 - 2002 URL only available to IEEE members2. ̂ Note that in the band 11.2–12 GHz the working definitions of Ku band and X band

overlap; satellite communications engineers would generally regard frequencies above 11.2 GHz as being part of the Ku band)

3. ̂ Mirabito, M.,& Morgenstern, B. (2004). Satellites: Operations and Applications. The New Communication Technologies (fifth edition). Burlington: Focal Press.

4. ̂ Satellite Communications: Advantage and Disadvantages

5. ̂ What is Ku band?

What is C Band?C Band is the original frequency allocation for communications satellites.

C-Band uses 3.7-4.2GHz for downlink and 5.925-6.425Ghz for uplink.

The lower frequencies used by C Band perform better under adverse weather conditions than the Ku band or Ka band frequencies.

C Band Variants

Slight variations of C Band frequencies are approved for use in various parts of the world.

Band TX Frequency RX Frequency

Extended C Band 5.850 - 6.425 GHz 3.625 - 4.200 GHz

Super Extended C-Band 5.850 - 6.725 GHz 3.400 - 4.200 GHz

INSAT C-Band 6.725 - 7.025 GHz 4.500 - 4.800 GHz

Palapa C-Band 6.425 - 6.725 GHz 3.400 - 3.700 GHz

Russian C-Band 5.975 - 6.475 GHz 3.650 - 4.150 GHz

LMI C-Band 5.7250 - 6.025 GHz 3.700 - 4.000 GHz

C Band Dishes

C Band requires the use of a large dish, usually 6' across. C Band dishes vary between 3' and 9' across, depending upon signal strength.

Because C Band dishes are so much larger than Ku and Ka Band dishes, a C Band dish is sometimes referred to in friendly jest as a BUD (Big Ugly Dish).

What is Ku band?

Sumber : http://www.tech-faq.com/ku-band.shtml

The Ku band (Kurtz-under band) is primarily used for satellite communications, particularly for editing and broadcasting satellite television. This band is split into multiple segments broken down into geographical regions, as determined by the ITU (International Telecommunication Union).

The Ku band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 11.7 to 12.7GHz. (downlink frequencies) and 14 to 14.5GHz (uplink frequencies).

The most common Ku band digital reception format is DVB (main profile video format) .vs the studio profile digital video format or the full-blown Digicipher II 4DTV format.

The first commercial television network to extensively utilize the Ku Band for most of its affiliate feeds was NBC, back in 1983.

The ITU Region 2 segments covering the majority of the Americas are between 11.7 and 12.2 GHz, with over 21 FSS North American Ku-band satellites currently orbiting.

Each requires a 0.8-m to 1.5-m antenna and carries twelve to twenty four transponders, of which consume 20 to 120 watts (per transponder), for clear reception.

The 12.2 to 12.7 GHz segment of the Ku Band spectrum is allocated to the broadcasting satellite service (BSS). These direct broadcast satellites typically carry 16 to 32 transponders.

Each provides 27 MHz in bandwidth, and consumes 100 to 240 watts each, accommodating receiver antennas down to 450 mm (18 inches ).

The ITU Region 1 segments of the Ku spectrum represent Africa and Europe (11.45 to 11.7 GHz band range and 12.5 to 12.75 GHz band range) is reserved for the fixed satellite service (FSS), with the uplink frequency range between 14.0 and 14.5 GHz).

Ku Band Difficulties

When frequencies higher than 10 GHz are transmitted and received used in a heavy rain fall area, a noticeable degradation occurs, due to the problems caused by and proportional to the amount of rain fall (commonly known as known as "rain fade").

This problem can be combatted, however, by deploying an appropriate link budget strategy when designing the satellite network, and allocating a higher power consumption to overcome rain fade loss. In terms of end-viewer TV reception,

it takes heavy rainfalls in excess of 100 mm per hour to have a noticeable effect.

The higher frequency spectrum of the Ku band is particularly susceptible to signal degradation- considerably more so than C band satellite frequency spectrum, though the Ku band is less vulnerable to rain fade than the Ka band frequency spectrum.

A similar phenomena, called "snow fade" (when snow accumulation significantly alters the focal point of your dish) can also occur during Winter Season.

Also, the Ku band satellites typically require considerably more power to transmit than the C band satellites. However, both Ku and Ka band satellite dishes to be smaller (varying in size from 2' to 5' in diameter.)

Ku Band Satellite Service Downlink Usage Frequency Range

The Ku band downlink uses frequencies between 11.7 and 12.7GHz.

The Ku band downlink frequencies are further subdivided according to their assigned use:

Ku Band Usage Downlink

Fixed Satellite Service 11.7 - 12.2GHz

Broadcast Satellite Service 12.2 - 12.7GHz

Services that can be found on the Ku-band include educational networks, business networks, sports backhauls, tele- conferences, mobile news truck feeds, international programming, and various SCPC (Single Channel Per Carrier) transmissions of analog audio, as well as FM audio services.

If you already have a operational C-band system in place, you can retrofit it to accept Ku band frequencies.

In order to do so, you will need to obtain a Ku-band LNB as well as a C/Ku band feed-horn, plus some coax cable for your Ku-band LNB.

As for the coax cable recommended- RG-6 is optimal for low loss in the 950-1450 frequency range- what Ku-band LNB processes. However, if RG-59 is your only viable option, it'll work in a pinch.

Ku Band Dish Antenna Compatibility

Iif you have a solid dish, you should have no problem converting from C band, to Ku band.

However, with a mesh dish- if the "holes" in the mesh are greater than a quarter inch, the chances of computability are not in your favor, due to the fact that your dish won't reflect Ku-band signals properly.

Therefore, you'll want to strongly consider upgrading to either a solid dish, or a mesh dish in which the hole size under 1/4", and ideally you'll want a dish that is 1 piece (or at least very few pieces); as 4 section dish is more optimal than an 8 section dish.

The fewer the sections, the more accurate your parabola shape is and thereby the more difficult it is for your dish to become warped (the smaller the number of seams- the better). And insofar as dish mounts go, the H2H (Horizon-to-Horizon) dish mount is more desirable than a polar mount.

This is due to the fact that the Ku-band demands that the dish antenna system is well-targeted and able to closely follow the orbital arc, of which the H2H mount does quite admirably, as compared to a polar mount. Also, bear in mind that you will be adjusting both the azimuth and elevation, which can be a bit tricky occasionally.

Importance of Satellite Antenna Dish Parabola

The parabolic shape of your dish is of critical importance, as warpage causes signal degradation via mis-reflection, seriously down-grading your overall system performance. Some tape and string is all that is required to do a quick warpage check and some tape.

Anchor a piece of string, stretched as tight as possible, "north" to "south" across your dish face, edge to edge. You'll want to do the same thing again, with another piece of string, only "east" to "west" across the dish face- at 90 degree angles. Be sure that both strings are tight-

If the strings come together anywhere but the direct center, then your dish has sustained warp damage and needs to be bent back into proper parabola shape, for optimal performance. If they connect in the center of your dish, likely that your dish is not warped.

So therefore, you'll want to use either the tri-supports or quad supports , as they will greatly assist in keeping your Ku-band feed-horn highly stable, even in high winds.

When your button-hook feed moving in the wind, your Ku-band reception can can easily drop out. By putting guy-wires on the button-hook feed, you'll create the much-needed support, in the event you are not able to obtain a tri support or quad support.

What is Ka band?The Ka band uplink uses frequencies between 27.5GHz and 31Ghz and the downlink uses frequencies between 18.3 and 18.8Ghz and between 19.7 and 20.2Ghz.

Ka band dishes can be much smaller than C band dishes. Ka band dishes vary from 2' to 5' in diameter.

Ka band satellites typically transmit with much more power than C band satellites.

The higher frequencies of Ka band are significantly more vulnerable to signal quality problems caused by rainfall, known as rainfade

What is L band?L band is a fequency range between 390MHz and 1.55GHz which is used for satellite communications and for terrestrial communications between satellite equipment.

The high frequencies utilized by C band, Ku band, and Ka band would suffer from high signal loss when transported over a copper coax cable such as an Intra-Facility Link.

An LNB is used to convert these higher frequency bands to L band, which can be transmitted over the IFL and processed by the IDU.

Some satellites transmit on L band, such as GPS satellites.

What is S band?S band is a frequency range from approximately 1.55 to 5.2GHz which is used for Digital Audio Radio Satellite (DARS) satellite radio systems such as Sirius Satellite Radio and XM Satellite Radio .

Vsat 120

General Features

The VSAT 120 is designed for receiving and transmitting in Ku band.

The high reliability and stability in aiming is determinant in making this antenna the most advanced equipment in maritime satellite communications, allowing transmission and reception in every weather condition with excellent signal quality.

The heart of the system is the inertial solid state stabilization system installed on the antenna. The VSAT is also provided with an automatic spiral search that allows faster satellite pointing procedure.The two systems together make the antenna the most effective equipment you can find on the market.

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The advanced solutions adopted should not impress too much.The totally integrated GPS and the internal Gyro interface device make the antenna a definitely user friendly apparatus.The A.C.U. needs just the operator to select the satellite to point.

DOWNLOAD BROCHURE

technical characteristics Active stabilization on the three orthogonal axes.

· Gyroscopic compensation of ship movements in yaw, roll and pitch.· Pointing capability with satellite in zenith position.· Automatic search, pointing and tracking.· Satellite identification through Integrated DVB-S receiver

· Step tracking for antenna pointing optimisation.· Simplifyfied satellite selection and search

The system is composed by two major blocks :

Above deck equipment, under a radome:· Stabilized pedestal with rotary joint.· Parabolic carbon fibre antenna, feed and orthomode tee· Transmitting/receiving set for Ku bandUnder deck:· Antenna Control Unit.· Modem

Type

front fedParabolic dish 1.2 mFrequency band KuTransmission frequency 13,75 ÷ 14,50 GHzReceive frequency 10,70 ÷ 12,75 GHzTransmit gain >43,2 dBi @ 14,25 GHzTx Beam width +/- 0.36 °Receive gain >41,5 dBi a 12,70 GHzPointing losses <1 dB ( ± 0.21 ° )Sidelobe patterns Eutelsat EESS 502 standard M

Sumber : http://www.vsat-technology.com/our-products/vsat-antenna/vsat-120/

What are Satellite Systems?The basic types of satellite systems include geostationary (GEO), Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Highly Elliptical Orbit (HEO) satellites. There are also public and private satellite systems such as Television Receive Only (TVRO), Direct Broadcast Satellite (DBS), Global Positioning System (GPS), and multibeam satellite operations.

Geosynchronous satellites orbit the Earth on repeatedly regular points over time. Each GEO satellite is stationary over one spot above the equator and therefore does not need any tracking from receiving and transmitting antennas on the Earth. GEO satellites enable the coverage of weather events. They are especially useful for monitoring severe local storms and tropical cyclones. They are best for television transmission and high-speed data transmission.

Low Earth Orbit (LEO) satellite systems fly very closely to the surface of the Earth, up to 1,500 kilometers in altitude. They deliver more significant voice quality over GEOs and transmit signals with a small margin of delay. Some LEO systems are designed for satellite phones or global mobile personal communications systems . These can carry voice traffic among other data formats.

Medium Earth Orbit (MEO) satellite systems operate at about 10,000 kilometers above the Earth, making it lower than GEO orbits but higher than LEO orbits. They have a larger capacity than LEOs. This enables them more flexibility in satisfying shifting market demands for voice or data services .

Highly-elliptical orbit (HEO) satellite systems orbit the Earth in an elliptical path unlike the LEO's and GEO's circular paths. Its elliptical orbit allows a wider view of the Earth and maximizes the amount of time each satellite spends in viewing populated areas. It therefore requires fewer satellites than LEOs while providing an excellent line of sight.

TVRO (Television Receive-Only) and DBS (Direct Broadcast Satellite) are satellite TV systems. TVRO relies on unencrypted feeds transmitted using open standards. They are also often referred to as C-Band Satellite TV, Big Dish TV, or Big Ugly Dish (BUD).

DBS works on higher frequencies. It is capable of transmitting higher power signals. DBS was primarily intended for home reception. This is why it is also known as Direct to Home satellite.

DBS satellites are owned by satellite TV providers. This means it is restricted to provide free channels.

A global positioning satellite system receives and compares the signals from orbiting GPS satellites to determine geographic location. Each satellite can transmit its exact location with a timed reference signal which the GPS uses to determine the distance between satellites. The location can be marked by calculating the point at which all distances cross. The information can be displayed in latitude or longitude format, or as a position on a computer map.

The multibeam satellite operation uses Spatial Division Multiple Access (SDMA) technology. This allows a single satellite to simultaneously communicate to 2 different satellites using several directional antennas.

What are Satellite Dishes?The major types of satellite dishes are motor-driven dishes, multi-satellites, VSAT, and ad hoc satellites. Other types include DTH, SMATV, CABD, automatic tracking satellite dishes, and big ugly dishes.

A motor-driven satellite dish is mounted on a pole which rotates around an axis to detect and receive various satellite signals in the sky. It is driven by a stepper motor, which can also be controlled to face any satellite position in the sky. It's standards, DiSEqC, USALs, and 36v positioners are supported by many receivers.

DiSEqC stands for Digital Satellite Equipment Control. It is a communication protocol specially designed to be used between a satellite receiver and a device that may be a multi-dish switch or a small antenna rotor. USALS, or Universal Satellite Automatic Location System, is a satellite dish motor protocol that can automatically create a list of available satellite positions in a motorized satellite dish setup. It is also known as DiSEqC 1.3, Go X, or Go to XX.

Multi-satellite dishes can pick up data transmissions from several satellite dishes at the same time. Its design enables simultaneous reception from multiple different satellite locations without having to reposition the dish.

A VSAT (Very Small Aperture Terminal) is a 2-way satellite ground station that provides two-way satellite Internet communication for consumers and private networks. It is commonly used to transmit narrowband data (credit card, polling, or radio-frequency identification ) or broadband data (satellite Internet access to remote locations, VoIP, or video).

Satellite operators configure VSAT networks in topologies. A star topology means the VSAT network uses a central uplink site to transmit data to and from each VSAT terminal via satellite. A mesh topology, on the other hand, minimizes the need for a central uplink site because VSAT terminals are allowed to relay data via satellite by acting as a hub to another terminal.

Ad hoc satellite dishes are used mainly as recipient reflector antennas of radio frequencies. It is easier to pick up signals on ad hoc satellite dishes when used with a DTH (Direct to Home) satellite.

DTH dishes are used in a single residence. SMATV, or Satellite Master Antenna Dishes, on the other hand, are shared among numerous dwellings. It is also called Communal Antenna Broadcast Distribution (CABD).

ATS (Automatic Tracking Satellite) dishes are used in vehicles in motion. They use gyroscopes to detect changes in position and Global Positioning System (GPS) sensors. Automatic tracking dishes use satellite identification data and an integrated Digital Video Broadcasting (DVB) decoder to identify the satellite it is pointing to.

The term "big ugly dish" is a colloquial term for a TVRO (Television Receive Only) satellite dish. The term refers to its large-sized receiving dishes. TVRO dishes are used to receive satellite television signals from fixed service satellites in the microwave C-band. The system relies on unencrypted feeds transmitted using open standards.

What is an LNB?An LNB - Low Noise Block (also called an LNC- Low Noise Converter), is used for communications (broadcast) satellite reception. The LNB is usually affixed either in or on the satellite dish.

The purpose of the LNB is to utilize the super heterodyne effect; and amplify and convert a wide block (band) of frequencies. This helps compensate the signal loss associated with typical coaxial cable at relatively high frequencies.

The term 'low noise' relates to the quality of the 1st stage input amplifier transistor, measured in either called Noise Temperature units, Noise Figure units or Noise Factor units.

Both Noise Factor and Noise Figure are easily converted into Noise Temperature units. A lower Noise Temperature rating is always better (i.e. an LNB with a Noise Temperature of 100K is 2x as good as one rated 200K).

The term 'Block' refers to the conversion of a higher block of microwave frequencies (received from the satellite- typically in the range 4 GHz to 21 GHz) being down-converted to a lower block range of frequencies for the receiver.

The "low-noise" part also indicates that amplification and mixing takes place prior to cable attenuation, in a circuit that requires no power supply or receiver.

With the high frequencies that satellites operate at, it is critical that the noise is controlled prior to signal processing.

An LNB helps keep the overall sound and picture of satellite TV from becoming greatly degraded, without the need of introducing a much larger dish reflector.

For wide-band satellite television carrier reception (generally 27 MHz wide band), the tolerance (accuracy) of the LNB local oscillator frequency needs to be in the range of ±500kHz,. This makes low cost DRO's (dielectric oscillators) feasible.

However, for reception of narrow bandwidth carriers (i.e. 16-QAM)- a highly stable, low phase noise dedicated LNB (local) oscillator is required.

They typically contain an internal crystal oscillator (or 10 MHz reference from the indoor unit) and a PLL (Phase-Locked Loop) oscillator, and naturally tend to be noticeably more expensive.

LNB Feedhorns (LNBF's)

DBS (Direct Broadcast Satellite) dishes use an LNBF, which matches the antenna's feedhorn up with the LNB.

Often times, small diplexers are utilized to distribute the resulting IF signal (typically in the 950 MHz to 1450 MHz range) and "piggyback" these signals with same TV cable that carries lower-frequency (terrestrial) television signals from a typical outdoor (terrestrial) antenna.

The TV set receiver also has another diplexer that separates the signals.

Universal LNB's

A universal LNB can receive both polarizations and the full range of frequencies in both the Ku and C satellite band.

Some LNB's can receive both polarizations simultaneously (through 2 different connectors), while other LNB's have either switchable or adjustable polarization.

Typical Universal LNB specifications are:

Local Oscillator (LO): 9.75 GHz /10.6 GHz Frequency: 10.7 GHz-12.75 GHz

Noise Figure (NF): 0.7 dB

Polarization: Linear

Standard DBS LNB example:

Local Oscillator (LO): 11.25 GHz Frequency: 12.2 GHz-12.7 GHz

Noise Figure (NF): 0.7 dB

Polarization: Circular

Typical North American C-band LNB specs:

Local Oscillator (LO): 5.15 GHz Frequency: 3.6-4.2 GHz

Noise Figure (NF): 15 to 100 Kelvins (uses Kelvin ratings as opposed to dB rating)

Polarization: Linear

Dual and Quad LNB's are multiple LNB's contained in one package, to allow for multiple receivers (on one dish).

A Dual LNB consists of 2 universal LNBs (affixed at a small offset angle in a single housing), and uses only one "F" connector and coaxial cable connection to the converter box.

Though also a Dual LNB system, the Monobloc LNB has only one output and only one (satellite) transmission is viewable at a time, as compared to dish systems which have two or more separate LNB's, each connected to separate receivers, in which both transmissions can be simultaneously viewed or recorded.

The Monobloc LNB was specifically designed to receive signals from satellites that are spaced very close together. For example, parts of Europe use a Monobloc LNB to receive the Astra 1 (19E) and Hotbird (13E) satellites, eliminating the need for an expensive rotator.

Quad Universal LNB (a.k.a. Quad-Output LNB)

The Quad Universal LNB can accommodate four separate receivers, as each receiver has independent control of band and polarization via 13v. and 17v. and 22kHz on/off switching respectively.

This LNB is primarily deployed in the Sky Digiboxes (with 2 LNB inputs and internal hard disks for recording one program while you're watching another).

Two LNB outputs would go to one "Sky Plus" Digibox, leaving the other 2 LNB outputs for either 2 standard Digiboxes or to one additional Sky Plus Digibox.

OCTO LNB's

An OCTO LNB is the same as above, except that it has 8 independent outputs.

Quattro Universal LNB's

This is a 4-output LNB, specifically designed for use as a "head end" I.F. distribution system (for apartment complexes). LNB's can generally supply (up to) 16 outputs for separate dwellings or Digiboxes. The 4 outputs of the Quattro Universal LNB are:

Low band horizontal polarization High band horizontal polarization

Low band vertical polarization

High band vertical polarization

As a general rule of thumb, any standard (universal) LNB will work with any circular (prime focus) dish or offset focus dish. Though actually taller than it is wide, an offset focus dish appears circular, as far as the LNB is concerned.

However, dishes that are wider than they are tall require a special LNB.

LNB's that are used for satellite TV reception contain DRO's (dielectric resonator stabilized local oscillators), which is a 'pellet' of material that resonates at the required frequency.

A DRO is relatively unstable, as compared to a quartz crystal resonator or oscillator.

Tolerances vary by as much as +/- 250 kHz to 2 MHz (Ku band), which includes the extremes of the full operating range.

Because most TV carriers are quite bandwidth-wide (i.e. 27 MHz band) even a 2 MHz error can successfully be received.

Though PLL LNB's are typically more expensive, the advantage of deploying an external reference PLL LNB is that constant temperature stability is much easier to maintain.

LNB Supply Power

The DC supply (typically in the 13v. to 19v. range) is cable line-fed to the LNB, and it is often times possible to alter the polarization by changing this voltage.

Alteration via the frequency band is also possible, albeit less common. Efficiently weather-proofing the outdoor connector is critical, as oxidation and corrosion occur rapidly. This, in turn, directly relates to signal degradation.

Both the outer and inner conductors must make solid electrical contact.

High resistance will cause the LNB to switch permanently into the low voltage state, over time, and lead to overall signal deterioration.

If you are physically trouble-shooting your system, be aware that the electrical antenna contacts between the BUC chassis and LNB are often times difficult to navigate, and 'earth loop' currents may also propose a problem.

As a matter of fact, it is entirely possible to become severely shocked in discovering 50 Hz or 60 Hz AC Mains currents on the outer conductors. Do be extremely cautious.

The quality and smoothing of the DC supplies used for the LNB's is also of great importance.

Testing an LNB

Check the ammeter drawing the DC current from the power supply (approx. number of mA's provided by the manufacturer).

Poor quality (or corroded) F type connections are the most typical cause of concern.

The center pin (of the F connector plug) should stick out ~ 2mm, away from the threaded surrounding ring.

A satellite finder power meter is also helpful. By pointing the LNB up at outer space (clear sky), the noise temperature contribution from the surroundings becomes negligible.

The meter reading will directly correspond to the noise temperature of the LNB.

If, for example, pointing the meter to outer space reads 100K (K is short for Kelvin, which measures absolute temperature), then you point the LNB towards the ground (say at a temperature of approximately 300K), the noise power meter reading should go up accordingly, to roughly 400K (100K +300K).

LNBs that fail on a particular polarization (or particular frequency band), may only do so at certain temperatures.

If you're attempting to replace an LNB in a VSAT system, be sure to check the both the supply voltage and the transmit reject filter; as continuously blowing up LNB's can get cost-prohibitive, quite rapidly.

Overloading an LNB

If you have a very large dish (i.e. ~7m diameter), and aim it at a satellite with signals intended for small dish antennas (i.e. ~70cm diameter), then the overall 20 dB increase in signal strength (being fed into the LNB) may be ample enough to overload some of the internal transistor amplifier stages.

Because this is not always obvious, it is wise to measure the composite output power of the LNB (using a power meter) and compare this with the -1 dB compression point supplied by the manufacturer.

Alternatively, you can do an antenna pattern test (on both a high power and a low power satellite). Any non linearity problem (with the high power satellite) will become clearly discernible.

To overcome this problem, you may need to invest in a special LNB (low gain or high power output level), if you have a large dish.

The "poor man's" field expedient means of fully testing an LNB is to hook it up to the desired dish (aligning the dish and LNB) and connect it to a satellite receiver.

Note the time of day and standard thermometer temperature, and check to see if each channel is there.

If all channels are present, take note and wait until there is a temperature variance of ~40 to 50 degrees higher or lower (Fahrenheit), and perform the exact same test again.

If it continues to work through a net temperature swing of at least 40 degrees, then the LNB should get you by for at least a while.

Keep in mind, however, that the reverse is not necessarily true. Missing channels can also be due to a faulty of the cable, receiver, or the dish (due to distortion, warpage, or misalignment).

Good old-fashioned process of elimination (by swapping the dish, the cable and the receiver), and bearing in mind that not all receivers work correctly with all LNB's will go a long way in aiding your trouble-shooting endeavors.

Also bear in mind that while a cheap satellite finder meter will give you the average strength of all frequencies, and an expensive satellite finder meter can let you target specific frequencies- neither will indicate to you whether frequencies are missing.

Lastly, most testers and meters draw off of low amperage battery power. If the battery can not supply enough current to the LNB, it'll ultimately give you a false reading.

An LNBF is an LNB with an integrated feedhorn.

Most LNB's in use today are actually LNBF's.

A Dual LNB is an LNB with two outputs.

A Dual LNB will enable you to connect two televisions to your satellite dish and tune into different channels on each television.

Triple and Quad LNB's are also available, for viewers with more than two television receivers.

What is a Linear LNB?LNB stands for low noise blocker and it is essentially an amplifier on the end of your small satellite TV dish or communications dish. The "Linear" portion of Linear LNB stands for the characteristics of the radio waves that are transmitted via the satellite in space to your dish (LNB).

Two Types of Polarization

Circular Polarization

Circular polarization is a characteristic of radio waves that are transmitted from a satellite in space, in which the actual radio waves rotate in a spiral. The spiral of radio waves either rotates clockwise or counter clockwise. A great analogy of how circular radio waves approach your satellite dish (LNB) is by picturing an airplane propeller. The airplane propeller follows a specific path, but as it approaches the radio wave is spinning vertically.

Linear Polarization

Linear Polarization is the characteristic of radio wave in which the radio wave rotates on a single horizontal plane. A great analogy is instead of an airplane propeller, the radio wave approaches your satellite dish in the form of a helicopter rotor. The radio waves spin horizontally.

Besides the direction of the wave being either horizontal or vertical, satellite receivers usually only are able to work with one type of polarization. However, they are able to pick up both signals, the difference is about 50% loss in signal strength (-3dB).

Determining Polarization

Usually Linear Polarized LNB's will use specific terms to describe their polarization. They are either "FSS" or "FTA". You should also note that a Universal LNB is always linear. Circular polarized LNB's usually use the terms "DSS" or "DBS" to denote that its satellite signal is polarized in nature.

What is Downlink?Downlink is the signal path from a satellite towards the earth.

The opposite of downlink is uplink. Uplink is the signal path from an earth station towards the satellite.

Downlink Frequencies

Satellite Band Downlink Frequency

C Band 3.7 - 4.2 GHz

Ku Band 11.7 - 12.7 GHz

Ka Band 18.3 - 20.2 GHz

What is Uplink?Uplink is the signal path from an earth station to a satellite.

The opposite of uplink is downlink. Downlink is the signal path from the satellite toward the earth.

Uplink Frequencies

Satellite Band Uplink Frequency

C Band 5.925 - 6.425 GHz

Ku Band 14 - 14.5 GHz

Ka Band 27.5 - 31 GHz

What is VSAT?VSAT is an abbreviation for a Very Small

Aperture Terminal. It is basically a two-way satellite ground station with a less than 3 meters tall (most of them are about 0.75 m to 1.2 m tall) dish antenna stationed. The transmission rates of VSATs are usually from very low and up to 4 Mbit/s. These VSATs' primary job is accessing the satellites in the geosynchronous orbit and relaying data from terminals in earth to other terminals and hubs. They will often transmit narrowband data, such as the transactions of credit cards, polling, RFID (radio frequency identification ) data, and SCADA (Supervisory Control and Data Acquisition), or broadband data, such as satellite Internet, VoIP, and videos. However, the VSAT technology is also used for various types of communications.

Equatorial Communications first used the spread spectrum technology to commercialize the VSATs, which were at the time C band (6 GHz) receive only systems. This commercialization led to over 30,000 sales of the 60 cm antenna systems in the early 1980s. Equatorial Communications sold about 10,000 more units from 1984 to 1985 by developing a C band (4 and 6 GHz) two way system with 1 m x 0.5 m dimensions.

In 1985, the current world's most used VSATs, the Ku band (12 to 14 GHz) was co-developed by Schlumberger Oilfield Research and Hughes Aerospace. It is primarily used to provide portable network connection for exploration units, particularly doing oil field drilling.

Implementations of VSAT

Currently, the largest VSAT network consists of over 12,000 sites and is administered by Spacenet and MCI for the US Postal Service (USPS). Walgreens Pharmacy, Dollar General, CVS, Riteaid, Wal-Mart, Yum! Brands (such as Taco Bell, Pizza Hut, Long John Silver's, and other fast food chains), GTEC, SGI, and Intralot also utilizes large VSAT networks. Many huge car corporations such as Ford and General Motors also utilizes the VSAT technology, such as transmitting and receiving sales figures and orders, along with announcing international communications, service bulletins, and for distance learning courses. An example of this is the "FordStar Network."

Two way satellite Internet providers also use the VSAT technology. Companies like StarBand, WildBlue, and HughesNet in the United States and SatLynx, Bluestream, and Technologie Satelitarne in Europe, and many other broadband services around the world in rural areas where high speed Internet connections cannot be provided use it too. A statistic from December 2004 showed that over a million VSATs were in place.

VSAT Configurations

Most of the current VSAT networks use a topology:

Star topology: This topology uses a central uplink site (eg. Network operations center (NOC)), which transports the data to and from each of the VSAT terminals using satellites

Mesh topology: In this configuration, each VSAT terminal will relay data over to another terminal through the satellite, acting as a hub, which also minimizes the need for an uplink site

Star + Mesh topology: This combination can be achieved (as some VSAT networks do) by having multiple centralized uplink sites connected together in a multi-star topology which is in a bigger mesh topology. This topology does not cost so much in maintaining the network while also lessening the amount of data that needs to be relayed through one or more central uplink sites in the network.

VSAT's Strengths

VSAT technology has many advantages, which is the reason why it is used so widely today. One is availability. The service can basically be deployed anywhere around the world. Also, the VSAT is diverse in that it offers a completely independent wireless link from the local infrastructure, which is a good backup for potential disasters. Its deployability is also quite amazing as the VSAT services can be setup in a matter of minutes. The strength and the speed of the VSAT connection being homogenous anywhere within the boundaries is also a big plus. Not to forget, the connection is quite secure as they are private layer-2 networks over the air. The pricing is also affordable, as the networks themselves do not have to pay a lot, as the broadcast download scheme (eg. DVB-S) allows them to serve the same content to thousands of locations at once without any additional costs. Last but not least, most of the VSAT systems today use onboard acceleration of protocols (eg. TCP, HTTP), which allows them to delivery high quality connections regardless of the latency.

VSAT Drawbacks

As with everything, VSAT also has its downsides. Firstly, because the VSAT technology utilizes the satellites in geosynchronous orbit, it takes a minimum latency of about 500 milliseconds every trip around. Therefore, it is not the ideal technology to use with protocols that require a constant back and forth transmission, such as online games. Also, surprisingly, the environment can play a role in slowing down the VSATs. Although not as bad as one way TV systems like DirecTV and DISH Network, the VSAT still can have a dim signal, as it still relies on the antenna size, the transmitter's power, and the frequency band. Last but not least, although not that big of a concern, installation can be a problem as VSAT services require an outdoor antenna that has a clear view of the sky. An awkward roof, such as with skyscraper designs, can become problematic.