If the audio frequency component is very distorted it is likely that the centerfrequency of the Varactor Modulator’s FM output needs adjusting slightly.
To do this, trim transformer T2 in the Varactor Modulator block as described
in Appendix 1 ‘Adjustnent of Tuned Circuits’.
The high frequency ripple is now removed by passing the signal through the Low
Pass Filter/Amplifier block.
I Monitor the input tp69 and the output tp73 of the Low Pass Filter/Amplifier
block (trigger by tp73) and note how the low pass filter has improved the
quality of the output signal.