It's All in the Baseband

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Steve Dove had some interesting observations on new developments in the all-digital baseband link between Wheatstone processors and major FM exciters. 


Regarding the recent development of an all digital link between the audio processor and the FM exciter:

"A less than obvious benefit to this is that 
the end-to-end frequency response of the system can now extend down to dc. It never really could before, since an oscillator capable of being frequency modulated also needed to be reminded where its center frequency was supposed to be, usually by a servo mechanism operating at and near dc. This precluded audio modulation getting too low in frequency. Indeed, over-enthusiastic amounts of LF energy could catapult a modulator out of lock and
the station off the air. (Ask me how I know.)"

On how SCA now fits into the new baseband192 scheme:

"The common way of dealing with RBDS and SCA signals (narrowband modulations typically centered at 57, 67 and 92kHz) has been to sum them into the MPX output in analog after the fact, which is obviously impractical in an all-digital stream. Doing so defeats the purpose and advantages. Already having the SCAs in the digital domain as part of the digital MPX stream gave us a complete, ready, baseband192 solution today without heroic redesigns to contend with."

Editor's note: Steve talks about SCAs and 192kHz as a digital baseband between Wheatstone AirAura, FM-531HD and VP-8IP audio processors and major FM exciters in this month's issue of Radio magazine.


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