| 摘要 |
1. A pilot signal demodulator for stereo television reception or television-2-channel sound reception, as the case may be, characterised in that a periodic signal (fH ) transmitted to the receiver with a video signal is used as a theoretical value for a control circuit functioning in accordance with frequency synthesis techniques (PLL system), connected to the theoretical value input of the phase detector (PD) of said control circuit, that the output of the follow-up oscillator (VCO) of this control circuit is connected to the actual value input of the phase detector (PD) via a controllable phase shifter (PHS), that further the signal (fP ) to be demodulated serves to set two mixer stages (M1, M2) whose other signal inputs are influenced by a signal from the output of the follow-up oscillator (VCO) in such a manner that this oscillator signal is fed directly to the first mixer stage (M1) and with a phase shift of 90 degrees to the second mixer stage (M2), and the output signal of the first mixer stage (M1) is finally fed to the input of the phase shifter (PHS) via a low-pass filter (G) to control the operating state of the phase shifter (PHS), whereas the demodulated signal (AM) can be tapped at the output of a further low-pass filter (TP) controlled by the output of the second mixer stage (M2). |
