Show off any of your RTL-SDR or cheap SDR related projects.
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Joined: Sun Aug 02, 2015 1:37 pm


Post by tesmarin » Sun Aug 02, 2015 1:44 pm

Hello RTL-SDR community. I would like to share with you my little project that replicates the efforts of two German researchers Sec and Schneider to whom goes all the credit of making all of this possible. Video of their presentation is available here

Sec and Schneider have revealed it is possible to receive Iridium satellite pager signals using well known and inexpensive RTL-SDR hardware, they have also created and released software to decode the captured signal. You can get a copy from Github

From hardware perspective the most problematic part was to build an antenna capable to feed RTL-SDR dongle with strong enough signal from Iridium satellite. Cheap GPS patch antenna from eBay does the job quite well after small modification of removing the bandpass filter. This step is necessary as although Iridium satellite signals are in close vicinity of GPS band, bandpass filter cuts out the signal we want to receive. Another thing is that because GPS patch antennas are active antenna type we also need a suitable way to power integrated LNA with ~3-5V for that reason use of bias-t between the dongle and antenna is required. To further improve signal reception GPS patch antenna can be replaced with a proper Iridium patch antenna made by Taoglas.

In my tests I have used a few different types of RTL-SDR dongles and because of the frequency that the Iridium satellites are transmitting 1.626 GHz the most stable would be Elonics E4000 based devices. I found that it is possible to receive a stable signal using some of R820T2 based devices with additional advantage of higher signal to noise ratio as the new chipset is more sensitive however not all of the dongles works stable at this frequency.

So far I'm able to receive some signal and have it partially decoded by software from github unfortunately I'm not getting any real pager messages yet. I'm planning to modify the setup I currently use by reducing the length of antenna cables between antenna, bias-t and dongle, reduce RF noise by closing rtl-sdr dongle and bias-t in metal boxes, connecting the dongle to raspberry pi and putting the whole thing on the roof to get the best reception.

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Re: Iridium

Post by rtlsdrblog » Mon Aug 03, 2015 2:35 am

Very interesting, do you have any images of the mod you made to the GPS antenna? And what are you using to record the RAW file needed by this software?

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