Errors in this respect will degrade the 35–40 dB (maximum) channel separation expected with this system. In both cases it is essential that the relative phase of the regenerated 38 kHz sub-carrier is accurately related to the composite incoming signal. Because the system shown in Fig. 2.8 is more easily incorporated within an integrated circuit, it is very much the preferred method in contemporary receivers. Provided that adequate input filtration is employed in both cases there is no operational advantage to either method.
This is only true if the input bandwidth of the sampling system is sufficiently large to allow noise signals centred on the harmonics of the switching frequency also to be commutated down into the audio spectrum.
In the circuit of Fig. 2.8, an equivalent process is done by sequentially sampling the composite signal, using the regenerated 38 kHz sub-carrier to operate a switching mechanism.Īdvocates of the matrix addition method of Fig. 2.7 have claimed that this allows a better decoder signal-to-noise (S/N) ratio than that of the sampling system. In the circuit of Fig. 2.7, this process is carried out by recovering the separate signals, and then using a matrix circuit to add or subtract them.
