I added this morning a post with links to the wav and mat files (matlab
files are centered on the VOR signal, and have limited sampling rate to 30
KHz)
feel free to ask further details if required
sylvain
2014-02-10 11:54 GMT+01:00 Ralph A. Schmid, dk5ras <ralph(a)schmid.xxx>xx>:
Thanks a lot - very interesting!
Ralph.
*From:* Sylvain AZARIAN [mailto:sylvain.azarian@gmail.com]
*Sent:* Sunday, February 09, 2014 8:55 PM
*To:* David Jacobowitz
*Cc:* jdow; Sylvain Munaut; osmocom-sdr(a)lists.osmocom.org; Ralph A.
Schmid, dk5ras
*Subject:* Re: odd results working at 250ksp/s
Hi,
With a lot of delay and my apologizes, as promised a while ago, I finally
published some quick notes on the VOR signal today.
The complete signal analysis as been posted on my blog at this page :
http://www.f4gkr.org/2014/02/in-depth-study-of-the-vor-signals/
I need to save the recorded WAV signals somewhere so people interested in
good SNR recordings would get it.
I decided to return close to the nearby VOR transmitter (Rambouillet,
south west Paris) and put the RTL SDR on my car rooftop and turn on the
laptop to capture some signals...
Best regards
sylvain F4GKR
2013-10-22 17:07 GMT+02:00 David Jacobowitz <david.jacobowitz(a)gmail.com>om>:
I originally posted about 115.8 and 116.8 MHz, both square in the VOR band
of 108 to 117.95. I might have sent something else in a PM, but if so it
was a typo. :-) I am definitely only interested in the VOR band right now
-- though, as you say, it is adjacent to commercial FM with its high power.
My application is simple in concept: A fully auomatic VOR-based
positioning system, a fallback from GPS. I want to scan the entire VOR
band, looking for signals in the standard VOR format that can be
demodulated. I do the initial scan with a fast sample rate and FFT, just
looking for peaks. From those, I examine the signals to see if it looks
like a VOR signal. From that list, I will "park" on each signal long enough
(~30s) to decode the VOR's morse code station ID. From that, I will have a
short list of VORs that I can currently receive. From those, if the
geometry is appropriate (I know the VORs positions from a database) I can
calculate a position.
The software then just round-robin tunes the VORs in range and continually
tries to calculate positions. If too many drop out, it returns to the
initial scan mode.
Not being able to receive this VOR or that VOR is not generally a problem,
but obviously, the more the better. With extra VORs I have better options
for choosing the closest ones or the ones with the best geometry.
This is actually quite difficult to test, because VORs can generally only
be received line-of-sight -- which means in the air. I'm a private pilot
but I found that flying and noodling with a laptop is too much trouble.
From my office window, on a high floor in Oakland, CA, I can receive one
VOR from the Oakland airport. And I have now discovered a ridge near my
home with a scenic overlook from which I can receive two.
I've tested the software enough to know that the initial scan function
seems to work, and the morse decoding kind of works, but I am not confident
I'll get it to work very well. (One transmitter's dit looks a lot like
another's dah.) The nav signal decoding is simple. (A 30 Hz AM modulated
tone is phase compared with a 30 Hz tone FM modulated at 9960 Hz. The phase
obtained is the azimuth to the station.)
If I ever get this working, I looking forward to sharing it with the
community. In the process of building this, I created a simple SDR toolkit
of DSP functions. It's like Gnuradio in concept, but 16b fixed-point, and
has no external dependencies, and C89, so is easier to build on weird and
limited platforms. It also has perl bindings. Compared to GR, it looks like
the work of a rank amateur just learning DSP, but I do like the concept of
there being a GR-like library out there, lightweight and embedded-friendly.
Regards,
Dave J
On Tue, Oct 22, 2013 at 3:06 AM, jdow <jdow(a)earthlink.net> wrote:
He sent me two frequencies in private email. These were in the FM
broadcast band (in the US). He probably needs to notch them out
in order to get adequate response.
As for wanting narrow bandwidth - I am not quite sure why he thinks
that is a benefit. I use a large FFT (about 10 Hz per bin) and use
the zoom control to see fine detail. (Different FFT settings suite
different uses. This one seems to be a good compromise with my two
needs. I'm too lazy to change it.)
{^_^}
On 2013/10/22 02:08, Sylvain Munaut wrote:
Effective filtering must occur between antenna and receiver. All the
problems that a saturated preamp and ADC cause can't be repaired by
software. Never.
But his original problem is not with saturated preamps or ADC ... it's
aliasing ... and that can be solved in the digital domain provided
fast enough ADC.
Cheers,
Sylvain