Micro Digital Satellite Receiver Bedienungsanleitung PDF herunterladen (Seite 7)

AN2677/D

DiSEqC Introduction

Digital Satellite Equipment Control (DiSEqC ) using MC68HC908QT/QY 7

The high-frequency circuit comprises D1, D2, and C3 (D6, D3, and C3 opposite

channel). Resistor R5 is used to switch the desired PIN-diode pair when the

supply voltage is present on the same LNB port. The opposite PIN-diode pair

is switched off by the reverse voltage. It is very important to design the correct

shape of the high-frequency circuit to match the impedance of the LNB to the

coaxial cable (both are 75 Ω).

The output pin 4 (PTA3) is used to send a message back to the IDU by two-way

communication (in levels higher than level 1.0). It’s possible to use a simple

circuit (transistor Q6 with associated components) to produce a pseudo

square-wave 22-kHz signal. This signal doesn’t comprise the high-frequency

disruptive components because of the value of the resistor R7 and the relatively

high capacitance of the coaxial cable line (about 50 nF to 100 nF). The two-way

communication option is not used in this design example.

The complete DiSEqC slave unit is packaged in a metal case with three

F-terminals, which is standard in satellite devices. The PCB is double-sided

with a bottom ground plane. The top side of the PCB is shown in Figure 4, and

the complete encased DiSEqC slave unit in Figure 5.

Freescale Semiconductor, I

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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Micro Digital Satellite Receiver Bedienungsanleitung Seite 7