Inmarsat

[jazzboypro]

Hello all,

For the past 2-3 weeks I've been into satcom. Equipment is as follow:
Radio: RSPDuo
SDR software: SDRUno
Antennas: SDR-KITS patch antenna and RTL-SDR patch antenna.
Decoders: JAERO and scytale-C

I am currently using the RTL-SDR antenna as it seems to be giving me stronger signals than the other antenna. The antenna is currently directed to Inmarsat-4 F3.

With JAERO i can decode 19 ACARS frequencies between 1545.014 and 1545.204
With scytale i can decode 7 STD-C frequencies between 1537.698 and 1539.683. 1537.698 is the one where i get message regularly.

I see some signals over the L-Band that neither of these decoders can decode (unless i'm doing something wrong).

I am currently picking up these signals:



According to JAERO, these are in the AERO C-Channel portion of the L-Band but i JAERO does not decode them (It is suppose to).

The signals were on and off at more or less regular intervals. As i finish writing this post, the signals are totally gone. I saw the signal for maybe 15 minutes or so but i don't for how long they were there to begin with.

Any ideas what those signals might be ? Is there anyway to decode them ? Are there any other decoders for L-band signals ?

Many thanks
73 de va2fcs

 

[thebaldgeek]

Glad to hear you are exploring L-Band.... This exact question comes up a LOT over the years. The trouble is that there must be over 100 other services on L-Band, not just from Inmarsat, but other L-Band satellites and so its hard to say for sure if what you are seeing is even coming from that bird.... The bottom line is, its hard for a hobbyist to know as not all of them are listed anywhere.
For ACARS, I have worked very closely with several people that monitor SATCOM and you should find an almost exhaustive list of active frequencies and modes on the bottom half of this page here: How to build an L-Band ground station.

 

[jazzboypro]

Thanks for the info. I will put this page in my favorites. I was not sure if it was possible to receive signals from different satellites without changing the placement of the antenna since they are geostationary. I did check the signal identification wiki but was i was seeing and hearing on my radio did not really match was i was looking at on the wiki even if it listed the signals as being Inmarsat. I suppose some of those signals might not even be possible to decode or not necessarily interesting.

Fortunately i will be able to install the antenna inside on the window sill and keep the same orientation, i will try it tomorrow to see if it has an impact on signal.

 

[thebaldgeek]

The patch antennas are very broad beamwidth so you can get a few geos without moving it.
From any Inmarsat there are dozens of signals that are not listed and undecodable for the likes of us.
If you take a look at the rest of the site (click the 'home link') you will find a good tip of NOT putting satcom antennas inside a window, so I was super happy to hear you are looking to put it outside one.

Enjoy the signals. Ask any questions. Great group of knowable folks here.

 

[jazzboypro]

The patch antennas are very broad beamwidth so you can get a few geos without moving it.
From any Inmarsat there are dozens of signals that are not listed and undecodable for the likes of us.
If you take a look at the rest of the site (click the 'home link') you will find a good tip of NOT putting satcom antennas inside a window, so I was super happy to hear you are looking to put it outside one.

Enjoy the signals. Ask any questions. Great group of knowable folks here.

I tried to install the antenna inside last night and it did not work at all no matter what i did. I put it back outside. I let JAERO run overnight and this morning i can see that i have a few Call_Progress messages in the SUs window. I will keep on experimenting.

 

[thebaldgeek]

Correct. Im sure you are reading the site and came across the description that windows more often than not have a coating on them to block UV light and be more thermally efficient. That coating very effectively blocks most radio frequencies. Its been a problem for many years, people look out the window and can see aircraft (ADSB) or can see where the geo satellite would be and don't understand why putting an antenna in the same place their eyes work does not work the same. Soon as they move it to the side and point the antenna through the wall or roof, it works much better than the window... Bottom line, antennas really need to go outside.
If you are interested in voice calls, those frequencies are listed on the same page tables as I linked before. Keep in mind you will only get one side of the call audio, the side from the ground. You need a C-Band satellite dish setup to get the cockpit audio: How to build a C-Band ground station.

 

[jazzboypro]

Correct. Im sure you are reading the site and came across the description that windows more often than not have a coating on them to block UV light and be more thermally efficient. That coating very effectively blocks most radio frequencies. Its been a problem for many years, people look out the window and can see aircraft (ADSB) or can see where the geo satellite would be and don't understand why putting an antenna in the same place their eyes work does not work the same. Soon as they move it to the side and point the antenna through the wall or roof, it works much better than the window... Bottom line, antennas really need to go outside.
If you are interested in voice calls, those frequencies are listed on the same page tables as I linked before. Keep in mind you will only get one side of the call audio, the side from the ground. You need a C-Band satellite dish setup to get the cockpit audio: How to build a C-Band ground station.

Thanks again. Lots of good info on the website. i did received audio this morning but it was just enough to see it was voice i could not tell what they were saying but at least i know it can be done.

I will concentrate on these as the Laurentides are very near from where i live.

1542,9775 AORW 98W Aero voice(8400)AMBE C-Chan 02/05 002/005 ARINC/SITA Laurentides, CA Global beam
1542,9825 AORW 98W Aero voice(8400)AMBE C-Chan 02/05 002/005 ARINC/SITA Laurentides, CA Global beam
1542,9875 AORW 98W Aero voice(8400)AMBE C-Chan 02/05 002/005 ARINC/SITA Laurentides, CA Global beam
1542,9925 AORW 98W Aero voice(8400)AMBE C-Chan 02/05 002/005 ARINC/SITA Laurentides, CA Global beam

I think my next step will be to replace the coax that came with the antenna by probably with some LMR. I will have to see what is available. Fortunately i won't be needing a long run as the antenna is near the radio and my operating position.

 

[737mech]

One question, How are you powering the antenna?

 

[jazzboypro]

One question, How are you powering the antenna?

The RSPDuo provides the bias-T voltage necessary for the builtin LNA in the antenna enclosure.