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TA0321

Lightning protection for LNB supply and control voltage regulator

STMicroelectronics 

3 22kHz Tone and DiSEqC (Digital Satellite Equipment Control) Encoding

TA0321

3 22kHz Tone and DiSEqC (Digital Satellite Equipment

Control) Encoding

In addition to selecting the polarization, the LNB needs to select the operating band. Indeed,

each reception band is divided in two bands:

● Low Band (10.7-11.7 GHz)

● High Band (11.7-12.75 GHz).

This is done with the use of a 22kHz tone frequency. A 22 kHz pulse-position modulated signal

of about 0.6 V amplitude is superimposed on the LNB's DC power rail. Its coding scheme also

allows the remote electronics to perform more complex functions. Traditionally, when other

encoding functions do not require the 22 kHz tone, simple presence or absence of this tone

selects the operating band by changing the local oscillator frequency of the LNB.

The complex encoding of the 22 kHz burst is done with a more sophisticated communication

bus protocol named the DiSEqC standard (Digital Satellite Equipment Control). The open

DiSEqC standard developed by the European Telecommunication Satellite Organization is a

well accepted worldwide standard for communication between satellite receivers and satellite

peripheral equipment.

The 22 kHz oscillator has to be a tone generator with specific rise and fall time. The wave

shape will be a quasi-square wave (sine with flat-top). The required frequency tolerance is

±2 kHz over line and temperature variations.

Table 1.

Band and polarization selection table

Parameters

22 kHz Tone

present

22 kHz Tone

absent

Operating band

High

Low

13 V

VDC

18 V

Vertical polarization

Horizontal polarization

Vertical polarization

Horizontal polarization

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