On Jun 23, 6:17 am, Paul Keinanen wrote:
Even with a proper S&H (ten nanosecond sampling and several
microsecond hold times) for decimation, the 280 Ksamples/s sounds a
bit low for FM broadcast detection.

The IF is 1.7 MHz which is sampled using a 13.6 MHz clock by the
AD9874
and decimated by a factor of 48 to produce the 280 Ksamples/s output.

Looking at:

http://en.wikipedia.org/wiki/Fm_broadcasting

I see that FM audio goes from 0 to 53 KHz and RDS is at 57 KHz.
The AD9874 decimation filter should prevent any signal from aliasing
into the bandwidth of interest and the resulting sample rate is
above Nyquist.

I'm missing something ... assuming no aliasing problems why is
a higher sampling rate necessary for recovering the audio and RDS?

-- John