gr-ais with osmosdr

friedtj at free.fr friedtj at free.fr
Tue Aug 7 12:58:03 UTC 2012


actually while I complete the real time decoding functionality for ACARS, I have a request
for the French speaking audience of this list (I believe I might have seen a couple of
.fr posts): I am completing an article for GNU/Linux Magazine France on this topic, and
would be grateful for a review by the experts (or actually also the non-experts to tell
me if what I wrote is worth discussing) of this list. The manuscript is available at

http://sequanux.org/jmfriedt/t/lm_sdr.pdf

I do try and describe there the development method I applied for writing several digital
mode decoders (not sure the method is the right one, but at least it is the one I use :)

Also if such a document might be useful for the non-French speaking community, I will
be happy to translate it to English as soon as time allows (ie probably after Sept 15th).

JM

----- Mail original -----
De: "Nick Foster" <nick at ettus.com>
À: friedtj at free.fr
Cc: osmocom-sdr at lists.osmocom.org
Envoyé: Lundi 6 Août 2012 18:20:30
Objet: Re: gr-ais with osmosdr

Looking forward to seeing it. Would be very nice to have ACARS data alongside ADS-B. 


--n 


On Mon, Aug 6, 2012 at 3:05 PM, < friedtj at free.fr > wrote: 


not sure what "I've been doing gr-air-modes development in anticipation of our ..." means, 
but since ACARS was being discussed as an addition to gr-air-modes, please let me announce that I am 
about to complete an ACARS-decoding block which was quite well tested on the rtl-sdr. 

JM 

----- Mail original ----- 
De: "Nick Foster" < nick at ettus.com > 
À: "Christian Gagneraud" < chris at techworks.ie > 
Cc: osmocom-sdr at lists.osmocom.org 
Envoyé: Dimanche 5 Août 2012 17:13:14 
Objet: Re: gr-ais with osmosdr 




On Sun, Aug 5, 2012 at 11:45 AM, Christian Gagneraud < chris at techworks.ie > wrote: 


Hi there, 

I saw a message in the July archive (I wasn't subscribed yet at that date) about updating gr-ais with osmosdr support. 
I was working on the same thing recently, so i decided to publish my fixes on top of Antoine's one. 
The result can be found here: 
https://github.com/chgans/gr- ais 

I got it working with both an FCD and an RTL: 
ais_rx.py --rate 96e3 --gain 30 --error -17 -d -D fcd=0 
ais_rx.py --rate 1024e3 --gain 30 --error -110 -d -D rtl=0 



Thanks for doing this. I haven't been looking at gr-ais lately as I've been doing gr-air-modes development in anticipation of our DefCon talk. Now that that's over, I'll have some time to integrate these changes and hopefully modernize a few things in gr-ais which I've been putting off. 



Strangely passing freq_err=XX parameter to the source (using -D), doesn't work, the use of --error is thus needed (which will do a set_freq_corr()). 

Antoine, if you want sample file, just let me know. 

Nick, are you willing to integrate these changing back in gr-ais, Apart from the added automatic decimation filter, the changes are not intrusive at all. 



Yep, I'll pull it back in. I'm also going to need your help vetting the changes against the FCD, as I don't have one. I do have an RTL dongle I can do some testing with. Have you had much success with AIS on RTL? 


--n 





The default settings for UHD are 256Khz sampling with decimation filter 4, with this change, the decimation is one when using FCD (96KHz fixed frequency) and 16 for RTL when used at 1.024MHz (this was the minimum working frequency for me). 
Or maybe would you prefer to allow the user to set it manually, and use this technique as a fall back only. 

Please let me know what you guys think. 

Thx, 
Chris 

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






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