FM stereo sub-carrier?

[colly0410]

Thanks for info. I was sort of on the right track with ' excess power being stolen from the main FM carrier.' If 10% is stolen from the main carrier no one notices - but 20%? Time to send for the cops. Never knew about B the BBC SCA gubins, will have a read through it in a bit, time for a mug of tea anyway so I'll put the kettle on...