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In teleports and satellite ground stations a method of inter-facility linking is needed to transport the RF payloads between the field-based antennae and equipment or control rooms. Transmission from satellites is received at the antenna in the higher frequency C, Ka and Ku bands. This is then down converted to the commonly used L band frequency range for handling the signals within the ground station. L band is chosen because much of the equipment is more cost effective when designed for this lower frequency. Historically, inter-facility linking has been performed using copper based coaxial cables which remains adequate in some installations where the distance between control and antenna location is short or data rates are low. However, site expansion necessitates the need to deploy longer interfacility transmission links and deliver increasing bandwidth.
In many locations site expansion has pushed conventional copper coax to its operational limit due to signal attenuation and degradation, which necessities the use of costly amplifiers. The subsequent rise in capital investment to expand sites and the compromised quality of service has created an opportunity for competing platforms. Fiber optic technologies have taken up this opportunity and a range of specifically designed, commercially available products offering cost effective inter-facility linking. Site engineers have been installing optical fiber for some years to fulfil long-term facility capacity requirements. Large scale multi site equipment installs have now reached widespread adoption in many leading satellite operators ground stations
ViaLite technology is found in standard and customised satcom installations, broadband VSAT systems, broadcast centers and military communication networks all over the world. Satcom is the most widespread application of ViaLite fiber optic links because they provide a reliable, high performance, cost effective alternative to conventional coax-cable systems for satellite communication systems. ViaLite fiber optic links create a transparent connection between satellite antenna up/down-converters and control room modems. The use of optical fiber overcomes problems inherent in copper based solutions including electrical interference, path length and electrical safety isolation. ViaLite has a proven track record in addressing customer applications in many satcom market segments including:
A typical satcom RF-over-fiber system consists of an optical transmitter and receiver linked by optical fiber. The system uses intensity modulation where the incoming RF signal directly modulates the intensity of a laser diode light source. This technique removes the need for any additional frequency conversion or digital conversion, and results in a very low noise and low distortion transmission path. ViaLite links offer exceptionally low phase noise performance, which makes them suitable for narrowband schemes. Intensity modulation also makes the links suitable for any modulation format making them inherently future proof. ViaLite is used for both up linking and down linking most common satcom frequency ranges. The ViaLite L-band link covers 950-2150MHz, suitable for the transmission of downconverted C, X and Ku band signals or directly transmitting L-band signals. For intermediate frequencies (70/140MHz) which are also transmitted across satcom installations the ViaLite IF link is used.
The ViaLite satcom product range includes options to suit many different applications. Different laser technologies are employed to produce short haul links for up to 2km (depending upon exact link budget), standard links for 2-40km, or long haul links for >40km distances. If fiber count is a problem this can be solved using the ViaLite CWDM platform that allows up to 8 transmit-to-receive channels to be passed through one fiber. Modules are also available to offer fully redundant systems and SNMP to integrate with M&C networks.
For VSAT applications ViaLite offers a range of different sized outdoor enclosures that allow the RF to fiber conversion equipment to be mounted close to, or even on, antennas or inside RADOMES. A range of rack options are available for the VSAT control end enabling the most cost effective solution to be designed, even for budgetary constrained installations.
The best dynamic range in the industry means that ViaLite links offer superb performance over a wide range of input signal levels, without the need for time-consuming and expensive set-up procedures.
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