# Questions about receiving signals of Inmarsat I-4 Satellites **URL:** \ **Category:** GNU Radio\ **Created:** [March 28, 2014, 9:42am UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116 "2014-03-28T09:42:36Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [March 28, 2014, 9:42am UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/1 "2014-03-28T09:42:36Z")
Hi, I am trying to receive signal from I-4 satellites of Inmarsat. I found that I-4 satellites have one global beam with 25 KHz bandwidth and several regional beams with 50 KHz bandwidth. However, I have scanned through frequency band 1525-1559 MHz and haven’t been able to find those beams. Anyone has experience of receiving Inmarsat satellites? Which downlink frequency should I tune to? I have tuned to frequencies listed on this website, still without any luck. [http://www.uhf-satcom.com/lband/](http://www.uhf-satcom.com/lband/) Setup: - USRP N210 + WBX - LNA with 30dB gain (ZHL-1217MLN) - Iridium antenna (I am not able to get specific antennas for Inmarsat…Iridium is at 1616 -1626.5 MHz and Inmarsat is at 1525-1559 MHz. I have used this antenna to capture signals around 1531 MHz successfully. I guess this antenna would not kill signals from Inmarsat.) Best regards, Cheng C. ---
**Author:** ![feo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e9bcb4/32.png) [@feo](https://www.ruby-forum.com/u/feo)\ **Post date:** [March 28, 2014, 11:55am UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/2 "2014-03-28T11:55:46Z")
I intend to make some tests with the antenna of my Inmarsat phone. When the phone receives something, I keep the antenna position and simply will plug the antenna to my SDR to see what happens. But I have no idea when I will find some time for this test… Ralph. From: discuss-gnuradio-bounces+ralph=removed\_email\_address@domain.invalid [[mailto:discuss-gnuradio-bounces+ralph=removed\_email\_address@domain.invalid](mailto:discuss-gnuradio-bounces+ralph=removed_email_address@domain.invalid)] On Behalf Of Cheng C. Sent: Friday, March 28, 2014 9:41 AM To: GNURadio D.ion List Subject: [Discuss-gnuradio] Questions about receiving signals of Inmarsat I-4 Satellites Hi, I am trying to receive signal from I-4 satellites of Inmarsat. I found that I-4 satellites have one global beam with 25 KHz bandwidth and several regional beams with 50 KHz bandwidth. However, I have scanned through frequency band 1525-1559 MHz and haven’t been able to find those beams. Anyone has experience of receiving Inmarsat satellites? Which downlink frequency should I tune to? I have tuned to frequencies listed on this website, still without any luck. [http://www.uhf-satcom.com/lband/](http://www.uhf-satcom.com/lband/) Setup: - USRP N210 + WBX - LNA with 30dB gain (ZHL-1217MLN) - Iridium antenna (I am not able to get specific antennas for Inmarsat…Iridium is at 1616 -1626.5 MHz and Inmarsat is at 1525-1559 MHz. I have used this antenna to capture signals around 1531 MHz successfully. I guess this antenna would not kill signals from Inmarsat.) Best regards, Cheng C. ---
**Author:** ![feo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e9bcb4/32.png) [@feo](https://www.ruby-forum.com/u/feo)\ **Post date:** [March 29, 2014, 2:06am UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/3 "2014-03-29T02:06:19Z")
1531 MHz signals from what? If you are using a patch antenna then it probably won’t have the bandwidth to cover 100 MHz. Lou KD4HSO Cheng C. wrote > - Iridium antenna (I am not able to get specific antennas for > Inmarsat…Iridium is at 1616 -1626.5 MHz and Inmarsat is at 1525-1559 > MHz. > I have used this antenna to capture signals around 1531 MHz successfully. > I > guess this antenna would not kill signals from Inmarsat.) > > Best regards, > Cheng C. – View this message in context: [http://gnuradio.4.n7.nabble.com/Questions-about-receiving-signals-of-Inmarsat-I-4-Satellites-tp47282p47298.html](http://gnuradio.4.n7.nabble.com/Questions-about-receiving-signals-of-Inmarsat-I-4-Satellites-tp47282p47298.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![feo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e9bcb4/32.png) [@feo](https://www.ruby-forum.com/u/feo)\ **Post date:** [March 29, 2014, 4:40pm UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/4 "2014-03-29T16:40:01Z")
This is what I found for inmarsat : [http://i.imgur.com/KygwHdD.jpg](http://i.imgur.com/KygwHdD.jpg) Some 200 kHz channels and some 50 kHz channels. There is also some 30 kHz channels with a small ‘X’ periodically in the spectrograme. Those are GMR-1 and probably leak through from Thuraya (either reflections off buildings, or my antenna polarization sucks). Or maybe inmarsat has some GMR-1 carriers, but I doubt it. Cheers, ``` Sylvain ``` ---
**Author:** ![feo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e9bcb4/32.png) [@feo](https://www.ruby-forum.com/u/feo)\ **Post date:** [March 29, 2014, 5:26pm UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/5 "2014-03-29T17:26:09Z")
> Did you use gr-phosphor for that plot? Of course 🙂 -F option of osmocom\_fft enables it directly. Cheers, ``` Sylvain ``` ---
**Author:** ![feo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e9bcb4/32.png) [@feo](https://www.ruby-forum.com/u/feo)\ **Post date:** [March 29, 2014, 5:04pm UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/6 "2014-03-29T17:04:33Z")
Did you use gr-phosphor for that plot? ---
**Author:** ![feo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e9bcb4/32.png) [@feo](https://www.ruby-forum.com/u/feo)\ **Post date:** [March 31, 2014, 3:12am UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/7 "2014-03-31T03:12:28Z")
Hi Sylvain, May I know what’s the setup you used for receiving the signal? The spectrum looks very clear. Best regards, Cheng C. ---
**Author:** ![feo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e9bcb4/32.png) [@feo](https://www.ruby-forum.com/u/feo)\ **Post date:** [March 31, 2014, 8:41am UTC](https://www.ruby-forum.com/t/questions-about-receiving-signals-of-inmarsat-i-4-satellites/240116/8 "2014-03-31T08:41:52Z")
Hi, > May I know what’s the setup you used for receiving the signal? The spectrum > looks very clear. - The antenna was a homemade helical antenna : [http://i.imgur.com/c6JaySJ.png](http://i.imgur.com/c6JaySJ.png) - It’s followed by a modified LNA23 (to be centered at 1550 MHz). This is a 30 dB LNA with a \< 1dB NF with a built-in filter. - Capture was made with a bladeRF Cheers, ``` Sylvain ```