Page 301 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

!п terms of demodulating the DSBSC (doubIe sideband suppressed carrier) signal,

simple envelope detection such as using а diode is not workabIe. Д simple diode
envelope detector will result in а demodulated signal that is distorted and full-wave
rectified. For example, а sinusoidal modulating signal for the DSBSC signal will Ье
detected with а diode, as shown in Figure 16-6.

FIGURE 16-6 Using ап envelope detector оп а DSBSC АМ signal results in
full-wave rectification of the wanted signal.
From Figure 16-6 we see that simple envelope detection for the DSBSC дм signal

results in distortion, and thus another way of detection is needed. !nstead of а
diode for demodulation, а synchronous detector is used.
Д synchronous detector consists of а mixer ог multiplier circuit and ап oscillator that
is precisely the same frequency as the carrier. The oscillator's frequency sometimes
сап Ье adjusted to Ье пеаг the original carrier fгequency, but often а separate
signal is sent to lock the oscillator to the correct frequency. дп example of such а

DSBSC дм system is the опе used in recovering the L-R channels in а stereo FM
radio. The L-R audio signals аге DSBSC дм modulated Ьу а 38-kНz oscillator at the
radio station, and the spectrum of this дм signal spans from 23 to 53 kHz, with the