Re: FM Carrier Recovery for AOA Calculation

[Marcus D. Leech]

On 01/09/2023 16:39, Marcus Müller wrote:
> Ah, nice! yeah, then this would work – but! any oscillator has drift, 
> so two local oscillators will not stay on the same phase for long; if 
> your first couple measurements are correct, but suddenly your 
> directions become very wrong, that's what I'd investigate.
>
> Cheers,
> Marcus
Looks like the BB60C supports an external 10MHz reference clock, which 
would be utterly mandatory for anything requiring
  mutual phase-coherence, whether that's *sufficient* depends very very 
much on the internal architecture of the BB60C.


> On 01.09.23 19:16, Michael Berman wrote:
> > The gr-aoa module has a calibration phase where you connect a source 
> > with a splitter and roughly equally lengthened cables to the two 
> > sources and it cross-correlates the two inputs to determine an 
> > initial phase difference.  Then, while the script is still running, 
> > you disconnect the calibration source and connect the antenna's, 
> > again with roughly equally lengthened cables to run the MUSIC algorithm.
> >
> >
> > Thank you very much,
> >
> > Michael Berman
> >
> > On Fri, Sep 1, 2023 at 11:00 AM Marcus Müller 
> > <marcus.mueller@ettus.com <mailto:marcus.mueller@ettus.com>> wrote:
> >
> >     If you don't know the relative phase of your two receiver chains, 
> > how are you going to
> >     know the direction of a signal?
> >
> >     On 01.09.23 17:37, Michael Berman wrote:
> > >     Marcus,
> > >
> > >     Thanks for the reply!  I apologize, the GR package is gr-aoa, 
> > > not gr-music, and can
> > >     be found here (https://github.com/MarcinWachowiak/gr-aoa
> > >     <https://github.com/MarcinWachowiak/gr-aoa>). The NOAA broadcast 
> > > is a NBFM signal.     I am using 2 Signal Hound receivers 
> > > (https://signalhound.com/products/bb60c/
> > >     <https://signalhound.com/products/bb60c/>) with 2 antennas 
> > > spaced on a beam.  Do I
> > >     need to synchronize the 2 receivers with an external clock, or 
> > > should they be fine
> > >     free running independently?
> > >
> > >
> > >     Thank you very much,
> > >
> > >     Michael Berman
> > >
> > >     On Fri, Sep 1, 2023 at 9:25 AM Marcus Müller <mmueller@gnuradio.org
> > >     <mailto:mmueller@gnuradio.org>> wrote:
> > >
> > >         Not familiar with the details of NOAA signalling, but isn't 
> > > the carrier of an FM
> > >         signal
> > >         *the FM signal*?
> > >
> > >         For a DoA estimate, you'd correlate the different receive 
> > > chains with each other
> > >         to get a
> > >         phase; so, as long as the signals do have some bandwidth 
> > > that makes the problem
> > >         less
> > >         ambiguous, it'd work with any signal. I'm sadly not familiar 
> > > with gr-music (and
> > >         can't find
> > >         it on cgran.org <http://cgran.org>), but MUSIC works as long 
> > > as the signals at
> > >         the different receive antennas
> > >         are correlated and noise is not. You do not have to 
> > > preprocess your FM signal!
> > >
> > >         Best,
> > >         Marcus
> > >
> > >         On 01.09.23 17:09, Michael Berman wrote:
> > >         > Does anybody know if there is a way to recover a carrier 
> > > of an FM signal to
> > >         use for an
> > >         > Angle of Arrival calculation?  I am using GNURadio and 
> > > gr-music and I am
> > >         trying to use the
> > >         > NOAA Weather Radio signals.
> > >         >
> > >         > Thank you very much,
> > >         >
> > >         > Michael Berman