Equipment
Special LNBs have been developed for use in single cable distribution systems. All four sub-bands of the Ku band (low frequency/horizontal polarity, high frequency/horizontal polarity, low frequency/vertical polarity, high frequency/vertical polarity) are received by a conventional front end, amplified and downconverted to the L-band, to be fed to a number of Single Cable Router (SCR) chips – one for each user that can be connected - to further downconvert the required section of the received spectrum to centre on the user band IF frequency. The LNB further includes a mixer to combine the user bands together and a microcontroller to receive the instructions as to which frequency is required by each user and control the SCR chips.
Alternatively, a single cable distribution system can use a conventional LNB feeding the four sub-bands to a separate SCR device, as a substitute for a traditional multiswitch, that needs a dedicated coaxial cable for every receiver (or tuner) connected.
Unicable LNBs and SCRs also include either a legacy mode of operation or a legacy output which provides conventional LNB IF for use with an installation of non-Unicable receivers.
A receiver required to operate in a single cable distribution installation can be essentially conventional. It should be able to tune to the user channel (within the normal IF tuning range) and modulate the LNB power voltage with the 22 kHz signal required for issuing DiSEqC commands. It will then require only software modification to operate as a single cable distribution receiver.
For correct operation, two-way splitters are required to feed the combined signal to each receiver. These allow bi-directional passage of both RF and DC signals, to provide for the passing of DiSEqC commands between the LNB and receiver(s).
As of March 2010, SES' Single Cable Distribution factsheet lists 88 receivers as supporting single cable distribution technology although this list is not exhaustive. Several receivers for the HD+ German high definition platform broadcast from Astra 19.2°E are compatible with the SCR system.
Read more about this topic: Single Cable Distribution
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