Recording scarce AIS bursts

GNU Radio
1

Hi list,

The problem with AIS is that if you are not in a busy place you might
have to wait for few seconds up to few minutes before a new message
comes in. Which is a bit annoying when you are doing live
experimentations.

I was thinking about recording only the raw message bursts, but i would
need a way to trigger the recorder such as to cut-off the blanks in
between the messages, but i didn’t find yet a solution to achieve that.
Would anyone have some tips to share on how to do that?

Another solution would be to record hours of data, and then apply the
same principle but off-line using a python script.

My triggering decision would be based on the signal level difference at
the carrier frequency and “outside enough” the carrier frequency.

Or maybe would anyone on that list have some “chatty” AIS data files to
share?

Chris

–
Christian G.,
Embedded systems engineer.
Techworks Marine
1 Harbour road
Dun Laoghaire
Co. Dublin
Ireland
Tel: + 353 (0) 1 236 5990
Web: http://www.techworks.ie/

2

You may not see optimal performance, but the standard or simple squelch
in
GNU Radio may meet these basic needs. I’ve used it for similar
functionality in other packet radio systems. I’m not sure what the
“carrier on” time is before modulation starts, so I can’t promise that
they
will work w/ the higher datarate of AIS.

Nick,

Any thoughts?

-John

3

On 27/07/12 17:39, John M. wrote:

You may not see optimal performance, but the standard or simple squelch
in GNU Radio may meet these basic needs. I’ve used it for similar
functionality in other packet radio systems. I’m not sure what the
“carrier on” time is before modulation starts, so I can’t promise that
they will work w/ the higher datarate of AIS.

Hi Nick,

It seems to do the job, at least it work for the strong bursts. Now i
think i just need to find the right gain settings to get the weaker ones
pass through.

thanks,
Chris

On Fri, Jul 27, 2012 at 8:40 AM, Christian G. <[email protected]
would need a way to trigger the recorder such as to cut-off the
Or maybe would anyone on that list have some “chatty” AIS data files
Co. Dublin

–
Christian G.,
Embedded systems engineer.
Techworks Marine
1 Harbour road
Dun Laoghaire
Co. Dublin
Ireland
Tel: + 353 (0) 1 236 5990
Web: http://www.techworks.ie/