video selector

It is sometimes useful, or even necessary, to use the same screen for more than one video source. Some simple video selectors used for this purpose suffer rather badly from crosstalk. The present circuit does not have this drawback: the unused chan- nel(s) is shorted out with a switch. When CI-flannel) 1 is switched in, electronic switches ES1and ES2are closed and ES4is open. The other channels) is effectively choked because ES5and ES6are both open and any residual crosstalk is shorted to earth by ES8. Each channel uses its own IC so that there is no risk of cross channel interference via the chips. As the switches have a certain impedance in the on state, there will be some losses when the output is ter- minated into 75 Q. It is, therefore, best to buffer the output; for instance, with the video buffer/repeater described elsewhere in this issue. The input of the video selector must be terminated into 75 Q. The —3 dB cl 7-70 video selector ES1 ES5 ES4 = IC1 = 4066 ES8 = IC2 = 40...