ST AN2056 APPLICATION NOTE

AN2056

APPLICATION NOTE

Extension of the SRC DiSEcQ 1 standard for control of Satellite Channel Router based one-cable LNBs

1 System overview

1.1Description

ST Microelectronics has introduced a new device that targets the LNB, multi-switch and SMATV market. This device, called SaTCR-1 (Satellite Channel Router), is able to translate a transponder to any location in the satellite bandwidth (950-2150 MHz). Multiple SaTCR devices coupled with band-pass filters and RF matrix allow to combine transponders from different polarizations and bands on a single coaxial cable.

The purpose of this document is to describe the AN2056 protocol extension used to control a LNB based on SCR technology.

1.2Standard LNB versus SaTCR LNB

A Ku-band satellite can provide up to 4.1 GHz of useful bandwidth (2 polarizations x (12750 MHz -10700 MHz)). A standard DVB-S tuner can receive frequencies from 950 MHz to 2150 MHz which means slightly more than 1 GHz bandwidth.

		13/18 volts detector	F
BPF	X	&
		22KHz detector
BPF	X
LO	LO	4 x 2
BPF	X	Matrix
	X	13/18 volts detector	F
BPF		&
		22KHz detector
		Twin LNB

To be able to receive all the available channels in the Ku-band using a conventional LNB, a settop box has to select the polarization and the local oscillator corresponding to the desired transponder. The polarization is selected by changing the voltage of the LNB supply (13 volts for vertical polarization, 18 volts for horizontal polarization). The local oscillator is selected by adding or not a 22 KHz tone on the LNB supply (when 22 KHz in on the highest LO is selected). Local oscillator frequency can be 9750 MHz or 10600 MHz depending on the location of the transponder. If the respective transponder is in the lower part of the spectrum (<11700 MHz) the 9750 MHz LO is selected, otherwise 10600 MHz LO is selected. The tuner has to be set to the correct frequency using the following formula:

Ftuner = Ftransponder - FLO

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With a LNB integrating SaTCR-1 devices, the transponder selection (polarization, LO selection and frequency translation) is done through a single DiSEqC command named ODU_ChannelChange (see Section 3.2.1 on page 8)

BPF

X

BPF

X

LO LO

BPF X

BPF

X

SaTCR

4 x 2

Matrix SaTCR

SaTCR twin LNB

I²C

DiSEqC

BPF 1210 MHz

F

BPF

1420 MHz

First stage of a SaTCR LNB (up to the matrix) is similar to a conventional LNB. As a consequence, the transponder frequency at the input of a SaTCR device is the same as Ftuner with a classical LNB:

Fsatcr_input = Ftransponder - F LO

Then, the SaTCR device should translate the transponder inside the bandwidth of its associated band pass filter. To perform that operation, the SaTCR VCO has to be set according to the following formula:

Fsatcr_vco = F satcr_input + Fbpf = Ftransponder - FLO + F bpf

In addition, SaTCR LNB includes new features that allow auto-detection of its parameters.

1.3What does this mean for the set-top box?

1.3.1Setup

The control of a SaTCR LNB requires more parameters than a standard LNB. Those parameters can be entered manually by the user or automatically detected by the set-top box. Automatic setup is recommended for all set-top boxes including tone detection capabilities (see Section 2.1 on page 5).

1.3.1.1Manual

In this mode, the set-top box should display an LNB setup screen where the user should enter the following parameters:

–• LNB type: the type of LNB used (see Table 3 on page 11 for SaTCR LNB application type)

–• Local Oscillator frequencies: depending on the LNB type, 1 or 2 frequencies should be entered

–• SaTCR band-pass filters frequencies: depending on the SaTCR application type, up to 8 frequencies should be entered.

1.3.1.2Automatic

In that mode, the set-top box LNB setup screen should contain a button that launches the LNB auto-detection procedure (see Subsection 2.2: Detecting LNB parameters on page 5) using

ODU_SCRxSignalON, ODU_Config and ODU_LOFREQ DiSEqC commands.

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1.3.2Tuning to a known transponder

Tuning to a known transponder is done by sending ODU_ChannelChange DiSEqC command (to select the polarization, the local oscillator and to perform frequency shifting) and tuning to the shifted frequency.

This procedure is described more in detail in Subsection 2.3: Searching for a channel on page 7.

1.3.3Scanning a complete satellite

Bandpass filter located in the LNB has limited bandwidth and this bandwidth can change from one application to another. In consequence, the most secure solution to scan the complete satellite is to split the bandwidth into small sections (typically 10 MHz), to shift them using ODU_ChannelChange DiSEqC command, and to scan them using the tuner as described below:

950 MHz	2150 MHz
	Frequency shifting
	Search range (10 MHz)
Tuner scanning
	Satellite scanning

1.3.4Standby mode

When the set-top box enters in standby mode or (in case of PVR boxes) when a tuner is not in use, its associated SaTCR should be set in power-saving mode using ODU_Power_OFF DiSEqC command.

1.4How to manage multiple set-top boxes?

When using several set-top boxes connected to the same cable, the following items should be taken into account.

1.4.1SaTCR allocation

In order to avoid having two set-top boxes or two tuners of the same set-top box trying to use the same SaTCR, each set-top box tuner should be allocated a dedicated SaTCR. In consequence, the LNB setup screen will display all SaTCR band-pass filters frequencies and the user will select one, two or more of them depending if the set-top box is a standard one (single tuner), a PVR (dual tuner) or multi-tuner box. When installing other set-top boxes, the user will have to take care not using an already allocated SaTCR device.

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1210 Mhz 1420 Mhz 1680 Mhz 2040 Mhz

1

2

3

4

PVR

SaTCR bandpass filter frequency allocation

1.4.2DiSEqC & power splitters

DiSEqC commands should always be sent above a 18 volts DC (see Subsection 3.1: SaTCR DiSEqC frames on page 8) in order to ensure proper connection to the LNB when set-top boxes are connected using power splitters.

Power splitter

13 volts								18 volts

13 volts

PVR

Sending DiSEqC through power splitters

2 Description of the software architecture

This chapter describes in detail the software routines that should be implemented inside the STB to support SaTCR LNB.

The basic commands need a standard DiSEqC 1 HW only. This ensures compatibility with most of today deployed boxes. Set-up is done in a manual mode as in today’s boxes. An innovative approach using an RF tone as back channel communication allows a bidirectional communication between the STB and the SaTCR LNB whilst keeping compatibility with DiSEqC 1. Set-top boxes featuring DiSEqC 2 can profit from the bidirectional communication of the DiSEqC 2 protocol as

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