RCA-Victor-Co-Inc-RK-295 电路原理图.pdf

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1、VOLUME R-22, MOST-OFTEN-NEEDED 1962 RADIO SERVICING INFORMATION P3-M MPX POWER R P2-M OUTPUT RESISTANCE VALUES ARE IN OHMS. RlOOO ALL CAPACITANCE VALUES LESS THAN 1.0 ARE IN MF, ALL VALUES 1.0 8 ABOVE ARE IN MMF EXCEPT AS NOTED. VOLTAGES MEASURED TO CHASSIS GROUND WITH VOLTOHMYST 8 SHOULD HOLD WITH|

2、N20% WITH 27$ V. B + SOURCE (PIN*4 OF P3-M). NO SIGNAL APPLIED. FM STEREO (MULTIPLEX) OPERATION Th* FM-Stereo (Multiplex) broadcasting system that has been approved by the FCC is compatible. This means that present FM timers not equipped for the reception of an FM-Stereo signal will be able to recei

3、ve a complete balanced program rather than only one channel, or an unbalanced program, as in former methods of stereocasting. The FM-Stereo composite signal is composed of three pieces of information: the L-f-R signal, the LR signal, and a 19 KC pilot signal. These are placed in the channel spectrum

4、 as shown. L-R “ L-R LOWER | UPPER SIDE BAND SIDE BAND Composite Signal The L-f-R signal is the in-phase combination of the left channel and the right channel information and is used to frequency modu late the main carrier. The LR signal is the out-of-phase com bination of the same channels and is u

5、sed to amplitude modulate a 38 KC carrier signal which is then suppressed leaving only the sidebands. This is the portion of the composite signal that, when matrixed with the L-f-R signal, separates the two channels. The 19 KC pilot signal is effectively the syncronizing signal and is used to reinse

6、rt the carrier in the LR signal, thus making a local oscillator unnecessary. Present FM tuners need only the L-f-R signal to reproduce the full and complete program. As this signal is the combination of the two stereo channels, none of the information is lost or suppressed for monophonic reproductio

7、n. In an FM-Stereo system, however, additional circuity is necessary to separate the combined channels. This is the function of the LR and 19 KC pilot signals. After reception through the normal FM channel of the receiver, in a FM-Stereo system, the signal from the FM detector (discrim inator or rat

8、io-detector) is fed into two amplifier stages (VIA & V2A). From the cathode of V2A the L-f-R signal is fed directly to the matrix from the Balance control which is a part of the cathode circuit, and the L R signal is filtered out and fed to T1 a mixing transformer. The 19 KC pilot signal is taken of

9、f at the plate of V2A and fed to a frequency doubler stage V2B. In V2B the grid is tuned to 19 KC and the plate is tuned to 38 KC. From the plate of V2B the 38 KC signal is fed to the mixing transformer, Tl, where the 38 KC carrier is reinserted in the LR signal. This signal is now demodulated in CR

10、1 and passed on to a phase- inverter stage (V1B). In the phase inverter the LR signal is taken off at the plate and the L-f-R signal is taken off at the cathode. These two signals are now fed to the matrix where they combine with the L-f-R signal. By simple algebra (L-f-R) -f- (L R) = 2L, and (L-f-R

11、) -f- (L-f-R) zz 2R, thus the left and right channels are recovered and fed to the stereo amplifier. This system, although similar in some respects to the color TV signal, differs in the fact that a local oscillator is not necessary for reinsertion of the carrier. Instead of sync pulse being supplied, an actual sync frequency is transmitted. It is also possible for a commercial service keying signal (S. C. A.such as is presently in use) to be transmitted in the composite signal. 100 收音机爱 好者资料库 RadioFans.CN