29-09-2016, 07:28 AM
The main mystery is how sound modulation is done. Clearly intercarrier but how do they get AM? Malcolm suggested a different but related chip might exist. Or it's actually FM but slope detected in the receiver. Or maybe the chip is being used in an unorthodox way to get AM. Can't see this happening as the sound is going into pin 13 as on the data sheet for the TDA5664.
My German is almost non-existent and I can't quite make out all the handwritten words on p41 of that article to type in google translate but...
The sound modulation is connected at pin 13 (Amplitude with pin 1 adjustable) ????????????????? L2 ????? carrier frequency.
L2 and C5 set the sound frequency. The example circuit on the TDA5664 data sheet shows a 10K damping resistor across the sound LC tuned circuit. This is omitted on the Meier design. I wonder if this encourages amplitude modulation, which would be spurious in the intended application of the chip, at the expense of FM.
My German is almost non-existent and I can't quite make out all the handwritten words on p41 of that article to type in google translate but...
The sound modulation is connected at pin 13 (Amplitude with pin 1 adjustable) ????????????????? L2 ????? carrier frequency.
L2 and C5 set the sound frequency. The example circuit on the TDA5664 data sheet shows a 10K damping resistor across the sound LC tuned circuit. This is omitted on the Meier design. I wonder if this encourages amplitude modulation, which would be spurious in the intended application of the chip, at the expense of FM.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
