ST AN2056 APPLICATION NOTE

APPLICATION NOTE

BPF

Twin LNB

Extension of the SRC DiSEcQ 1 standard for control of

Satellite Channel Router based one-cable LNBs

1 System overview

1.1 Description

ST Micr o el ec t ro nics has introduc ed a ne w de v ice that ta r g ets the LNB, mu lt i- s wit c h and S M ATV market. T his de vic e, c al led S aTC R-1 (S at ell it e Ch ann el R o ute r), i s ab le to t rans la t e a tr an spon de r to any lo ca t i on in the sat el lit e b andwidt h ( 9 50 - 2 15 0 MHz). M u lti ple SaTCR d evices co upled wi th band-pass filters and RF matrix allow to combine transponders from different polarizations and bands on a single coaxial cable.

The purp os e o f t hi s d oc ume nt i s t o de scri be t he A N20 56 pr oto co l e xt ens ion us ed t o c ontr o l a L N B based on SCR technology.

1.2 St andard LNB versus S aTCR 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.

AN2056

13/18 volts detecto r

22KH z detec tor

To be ab le to r e c eiv e all the available c hannels i n t h e Ku-ban d u si ng a co nventional LNB , a s ettop box has to select the polarization and the local oscillator corresponding to the desired

4 x 2 Matrix

13/18 volts detecto r

22KH z detec tor

transponder. The polarization is selected by changing the voltage of the LNB supply (13 volts for vertica l po lar iz atio n, 18 vo lt s for hori zon tal pol ari za tion ) . The lo cal os cil l ator is select ed by addi ng or not a 2 2 KHz ton e on t he LN B su pply (whe n 22 KHz in on th e hi ghe st LO is se lect ed) . Loc al oscillator frequency can be 9750 MHz or 10600 MHz depending on the location of the transponder. If the respective transpo nder is in the lower part of the spectrum (<11700MHz) 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:

tuner

= F

transponder

- F

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AN2056

BPF

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)

I²C

1210 MHz

1420 MHz

4 x 2

Matrix

SaTCR

SaTCR twin LNB

First st age of a Sa TCR LNB (u p to the ma trix) is simi lar to a conven tiona l LNB. As a consequ ence , the tran sponder fre quency at the input of a SaTCR device is the same as Ftuner with a classical LNB:

satcr_input

= F

transponder

- F

LO Then, the SaTC R device sh ou ld t ran slate the tr an s po nder ins ide the bandw id t h o f it s ass o ci ated band pass filter. To perform that operation, the SaTCR VCO has to be set according to the following formula:

satcr_vco

= F

satcr_input

+ F

bpf

= F

transponder

- FLO + F

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

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

DiSEqC

bpf

1.3.1 Setup

1.3.1.1 Manual

1.3.1.2 Automatic

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The control of a SaTCR LNB requires more parameters than a standard LNB. Those parameters can be en tered manual ly by t he us er or a utomat ical ly de tected by th e set- top box . Auto mati c setup is recommended for all set-top boxes including tone detection capabilities (see Section 2.1 on

page 5).

In this mo de , the s et -t op b ox shou ld di sp lay an LN B se t up scr e en w here t he use r shou ld en te r t he follo wing parameters:

–• LNB type: the type of LNB used (see Table3 on page 11 for SaTCR LNB application type) –• Local Osc il l at or f req ue nci e s: dep en ding on th e L NB typ e, 1 or 2 f req ue nci e s shou ld be ente r ed –• SaTCR band-pass filt ers frequencies: depending on the SaTCR appl ication type, up to 8

frequencies should be entered.

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.

1.3.2 Tuning to a known transponder

950 MHz

Tuning t o a kn own tra ns pon de r is do ne by se ndi ng ODU_ChannelChange DiSEqC com man d ( t o select the polarization, the local oscillator and to perform frequency shifting) and tuning to the shifted freq u ency .

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

1.3.3 Scanning 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:

Frequency shifting

Search range (10 MHz)

Tuner scanning

Satellite scanning

AN2056

2150 MHz

1.3.4 Standby 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.

1.4 How to manage multiple set-top boxes?

When usin g s eve ral set -to p bo xes co nnec ted to the sa me c abl e, the fo llowi ng ite ms shou ld b e taken into account.

1.4.1 SaTCR 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, tw o or mor e of the m depe ndin g if th e set-t op bo x is a st andar d one (singl e tu ner), a PVR (d ual tuner) or mu lti -tu ne r bo x. W he n in s tal li ng oth er s et -top bo xes , the us er wi ll have to ta ke ca re n ot using an already a llocated SaTCR device.

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AN2056

1 2 3 4

13 volts

18 volts

1210 Mhz

1420 Mhz

1680 Mhz

2040 Mhz

PVR

SaTCR bandpass filter frequency allocation

1.4.2 DiSEqC & power splitters

DiSEq C comma nds shou ld alway s be sent above a 1 8 volts D C (see Subsection 3.1: SaTCR

DiSEqC frames on page 8) in ord er to ensu re p r op er connec t io n t o t h e LNB whe n s et-top bo xe s

are conn ec t e d us in g power split ters.

Power splitter

PVR

Sending DiSEqC t hrough power splitters

2 Description of the software architecture

This chapter describes in detail the software routines that should be implemented i nside th e 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 u si ng an RF tone a s b ack ch an nel c om mun ic at i on allo w s a bid ir e ctio na l c om mun ic at ion 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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