I’ve been playing with my simple_fm_rcv application, with both RTL-SDR
and UHD devices. I’d like to be able
to implement some kind of AFT. I tried using the PLL detector block,
but was unable to arrive at a set of
parameters that produced anything but near-rubbish coming out of it,
even getting hints from
blks2impl/ So, I went back to a non-PLL WBFM block,
which is based on a quadrature

The UHD clock quality is very good compared to RTL-SDR, but FM stations
in North America are allowed
by the rules to be out by a couple of Khz, which makes a noticeable
difference if you aren’t tuned “bang on”.
The RTL-SDR has a crappy clock, so it can compound any offset problems
quite a bit.

Principal Investigator
Shirleys Bay Radio Astronomy Consortium