Indoor Unit For Satellite Tv Reception-3

EE 20 January 1987 INDOOR UNIT FOR SATELLITE TV RECEPTION 3 by J a- R v. Terborgh The circuit board described in this article is not, strictly speak- ing, indispensable for a fully operative indoor unit. But then, the optional add-on circuits are relatively simple to build on a single PCB, and may provide you with a number of quite useful extensions. Circuit description The circuit diagram of the op- tional extension board is shown in Fig. 18. The various functions it offers are best discussed by starting from the three possible positions of the front panel mode switch, S4a-b. 1. TUNE: S4a-b is set to position 1, as shown in the circuit diagram. Oscillator IC9 is disabled by the low level at its RESET input, pin 4. Electronic switch ES5 is closed, while ES4 is opened, so that the DC- coupled video signal, CVBS-1 (see Part 2) is routed to TV modulator IC16. The operation of this versatile RF chip will be reverted to. The RF board tuning voltage, Vtune, is taken from the output of s...