The wide signal in question is about 168 kHz. I’ve been able to see several
side-by-side like in other people’s pictures by using 9A4QAV’s helix.
Sent from Windows Mail
From: Henry Barton
Sent: Wednesday, May 4, 2016 1:08 PM
To: discuss-gnuradio@gnu.org
Thanks, Ian. So the I prefix is Inmarsat?
Sent from Windows Mail
From: Ian Buckley
Sent: Wednesday, May 4, 2016 12:47 PM
To: Kevin McQuiggin
Cc: Henry Barton, discuss-gnuradio@gnu.org
Henry,
Its important to realize that there are 3 generations of Inmarsat systems
currently in use. The I3 birds carry a lot of narrow band services for air to
ground and ship to shore as Kevin just described. As you move to I5 via I4 you
see higher, more modern broadband service start to appear.
-Ian
On Tue, May 3, 2016 at 9:34 PM, Kevin McQuiggin <mcqui...@me.com> wrote:
My error, typo I meant GMSK!!
Sent from my iPad
On May 3, 2016, at 9:31 PM, Kevin McQuiggin <mcqui...@me.com> wrote:
Hi Henry:
The narrowest channels are 600 bps MPSK, although in Inmarsat parlance they
call it "A-BPSK". There are 1200, 4800, 10200 bps channels as well, plus
faster ones I have not really considered yet.
The spec document describes it all.
I find the signal to be quite strong, perhaps check your polarization or
antenna pointing. You'll want RHCP for Inmarsat. Signals are well above the
noise floor for me. I'm using an Ettus B200.
Also, check out a program called "JAERO", the web site has lots of relevant
information.
My program isn't on github yet, I'm an old timer so I'm developing it locally.
I can release it once it's ready!
Kevin
Sent from my iPad
On May 3, 2016, at 8:31 PM, Henry Barton <kw...@outlook.com> wrote:
So the control channels are the narrow ones? I’m guessing the really wide ones
are the traffic. (On a side note, I’m kind of surprised that people [you and
killmore231] can get Inmarsat with a patch. I just barely see the signals with
9A4QAV’s helix and an SDRplay. However, Iridium comes in like a blowtorch.)
Anyway, can’t wait to see your program. Is it on Github?
Sent from Windows Mail
From: Kevin McQuiggin
Sent: Tuesday, May 3, 2016 10:02 PM
To: Henry Barton
Cc: discuss-gnuradio@gnu.org
Hi Henry:
I have an Inmarsat demodulator working for the lower speed control channels. I
am writing a program to decode the traffic, but this is not a trivial task.
Think on the order of 1000 lines of C. It is "almost" working, I am hoping for
valid output in the next week or so, depending on my free time.
My program is currently a standalone program, but once it's done it could
conceivably be converted to one or more gnuradio blocks.
I suggest the following document to give you background on the channel
specifications for Inmarsat:
http://www.icao.int/safety/acp/inactive%20working%20groups%20library/acp-wg-m-iridium-8/ird-swg08-wp07%20-%20old_amss_material_ch.4_plus_attachment.doc
The demodulation is fairly easy, read the spec document and the channel
characteristics are pretty well described. My gnuradio demodulator is based on
the GMSK demod block. I'm using a home brew patch antenna, and the LNA4ALL low
noise amplifier.
Kevin
Sent from my iPad
On May 3, 2016, at 12:45 PM, Henry Barton <kw...@outlook.com> wrote:
http://rtlsdrblog.rtlsdrblog.netdna-cdn.com/wp-content/uploads/2015/10/sdrplay_lband-1024x573.png
I didn’t see the widest signal (bright yellow) from this picture on
sigidwiki.com. Does anyone know what it is? If so, can it be decoded by
GNUradio? Thanks.
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