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644 RICHARDSON'S BLUEBOOK OF PROJECTION
grids act as the oscillating portion of the tube, others receive the signal from the r.f. amplifier. The output of the tube is the beat frequency which goes to the intermediate frequency amplifier.
(8) The intermediate frequency amplifier is quite similar to the one diagrammed in Figure 226 but the transformers are sometimes of the powdered iron core type and in themselves are very sharply tuned to accept only that intermediate frequency for which they were designed. Since the i.f. amplifier operates on one frequency only — the beat frequency — it has no variable condensers.
(9) The output of the i.f. amplifier goes to the second detector, which is the same as the demodulator or detector of Figure 226, and the output of the second detector of Figure 227 goes to an ordinary sound amplifier and thence to a loud speaker.
(10) The details of these common radio circuits of course cannot be given here ; this entire Blue Book could be filled with the details of radio circuits, and it still would not be large enough to hold them all. Such data are readily available in many books that deal with radio. The underlying principles are all that can be given here without sanctifying space needed for projection details that cannot be found in any other book.
The Television Receiver
(11) The television signal proper, ranging from 0 to 3,000,000 cycles per second, and impressed upon a carrier frequency which may be as high as 60,000 kilocycles, is received and reproduced by superheterodyne equipment in essentially the same way just described. The radio frequency amplifier section in the television receiver of course is built with r.f. transformers and variable condensers suited to accepting frequencies as high as 60,000 kilocycles ; the intermediate frequency section is tuned to possibly 7,000 kilocycles (instead of possibly somewhere around 500 kilocycles as in the case of a common broadcasting receiver), and the output of the second detector goes to a video amplifier capable of dealing with a