Re: FM Carrier Recovery for AOA Calculation

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

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
>>