Inmarsat Aero Changes

[Hutchp]

I have been monitoring Inmarsat voice and data channels for some time both at C and L band. I noticed recently (mid May) a big reduction in the number of 600bps channels on Alphasat. At the same time virtually all USAF Europe voice channel traffic moved from Alphasat to 3-F5 at 54W ( Strangely US Navy Europe traffic still on Alphasat). Wondered if this was a re-groom of traffic prior to the new Inmarsat I6-F2 satellite coming on station. Think I saw this was going in at 28W?
Also noted voice traffic at 1545.36MHz area on Alphasat using what looks like 21000bps ( 20Khz bandwidth.)

Hutch

 

[thebaldgeek]

In short. Yes.

In long.....
Man, its going to be a wild and turbulent ride for the rest of the year and into a bit of next I suspect.
Im heavily involved in the ACARS data collection from three ground stations. 143 over APAC, 98w over the Americas and 25e over UK/Euro.
Inmarsat is going to be bringing two of the I6 sats into play in short order.
So not only are the frequencies going to change, but also the satellite TLEs.
There is going to be drilling of holes and moving of dishes and recalibrating of tracking software just so we can start working on the SDR side of things.
Its going to take a lot of team work to try and keep things running during this change over.

 

[Hutchp]

Ok so I think it will be early 2024 for 2-F6 to be ready for traffic. The F6 satellites are L band and Ka band only (no C Band) I think. I have some Ka band kit so will be an interesting challenge to build a system for that. Wonder if they will migrate all 'classic' aero traffic to the new sats when on station. The F6 satellite has substantially more L band capacity then existing so will also be interesting to see how much the frequencies change

 

[thebaldgeek]

I have heard both 'keeping C-Band and adding Ka' and the 'Ka only' story from a lot of people....
Honestly, I don't know which camp to trust at this point..

 

[Hutchp]

No mention of any C Band payload in any Inmarsat documentation. Would make sense not to have C band, as that section of spectrum has been given over to terrestrial 5G applications in most countries now.

 

[Dark_sky]

Turned on my Aero ACARS & voice for 25E on this weekend for the first time in a few months and noticed a big change.
C1/C5 GES channels for both 600bps & 10500 almost half the usual signal strength. 90 GES doesn't seem to of changed signal strength wise.
As for voice literally no USAF traffic today except for the odd C-17 working out in the middle east.

Inmarsat are due to switch off Aero I/H services by the end of the year leaving only H+ which i believe will only support the higher 10500 channels. Likely will tie in with the I6-F2 once its up and running. As for voice = not sure what will happen with the current 8400 channels.

 

[Dark_sky]

I have been monitoring Inmarsat voice and data channels for some time both at C and L band. I noticed recently (mid May) a big reduction in the number of 600bps channels on Alphasat. At the same time virtually all USAF Europe voice channel traffic moved from Alphasat to 3-F5 at 54W ( Strangely US Navy Europe traffic still on Alphasat). Wondered if this was a re-groom of traffic prior to the new Inmarsat I6-F2 satellite coming on station. Think I saw this was going in at 28W?
Also noted voice traffic at 1545.36MHz area on Alphasat using what looks like 21000bps ( 20Khz bandwidth.)

Hutch

Hutch, do you know which frequencies you have been picking up the USAF Europe stuff on 54W?

 

[n5pwp]

I have noticed a degradation to the I-4 F3 sat at 98W degrees. I used to get about a dozen of the signals very well. Sometime earlier this year I noticed that the wave forms in JAERO are distorted and much weakened. Now I can only receive 1 1200 Bd signal. The 600 Bd signals are all weakened and distorted.

I'm using an RTL-SDR V3 dongle and a patch antenna. Throughout the day I will get a couple of the 600 Bd signals to eek up enough to finally lock but I used to be able to receive them all day long before. I don't know what has changed. Anyone else monitoring I-4 see anything like this? It started doing this before all the leaves popped back out on the trees so its no foliage related. The patch antenna is still aimed at the satellite the same. I believe i read somewhere that the 1200 Bd signals have more power so that might be why I get the one.

Mike

 

[Hutchp]

Hutch, do you know which frequencies you have been picking up the USAF Europe stuff on 54W?

Yes most of the USAFE traffic ,KC-135's etc voice channels have moved to 1546.82-1546.86 MHz range on 54W. Doesn't seem to be working too well for them though. I have noticed a huge increase in the number of failed calls and multiple call connect attempts.

Regards
Hutch

 

[dlwtrunked]

Hutch, do you know which frequencies you have been picking up the USAF Europe stuff on 54W?

I have noticed a degradation to the I-4 F3 sat at 98W degrees. I used to get about a dozen of the signals very well. Sometime earlier this year I noticed that the wave forms in JAERO are distorted and much weakened. Now I can only receive 1 1200 Bd signal. The 600 Bd signals are all weakened and distorted.

I'm using an RTL-SDR V3 dongle and a patch antenna. Throughout the day I will get a couple of the 600 Bd signals to eek up enough to finally lock but I used to be able to receive them all day long before. I don't know what has changed. Anyone else monitoring I-4 see anything like this? It started doing this before all the leaves popped back out on the trees so its no foliage related. The patch antenna is still aimed at the satellite the same. I believe i read somewhere that the 1200 Bd signals have more power so that might be why I get the one.

Mike

View attachment 144823View attachment 144824

You only receive one 1200 Bd signal because they only transmit only one and have for some time. Here is a MAY 2023 complete (or near complete list) of INMARSAT 54 and 98 Aero. Note many aero frequencies are spot rather than global beams. Some think frequencies have changed when they discover a spot beam they had not noticed before.

 

[Dark_sky]

Yes most of the USAFE traffic ,KC-135's etc voice channels have moved to 1546.82-1546.86 MHz range on 54W. Doesn't seem to be working too well for them though. I have noticed a huge increase in the number of failed calls and multiple call connect attempts.

Regards
Hutch

Thanks Hutch.
You also mention a reduction in 600bps on Alphasat but i'm still seeing the same amount there was a good couple of months ago??
The only change i have noticed is the signal strength with the C1/C5 channels. I'm i missing something obvious here?

For context this what i monitor and still see as of today

90 GES
1545.115 - 600
1545.120 - 600
1545.125 - 1200
1545.130 - 600
1546.013 - 10500
1546.027 - 10500

C1/C5 GES
1545.160 - C5 600
1545.165 - C5 600
1545.185 - C5 600
1545.190 - C5 600
1545.215 - C1 600
1545.220 - C1 600
1545.225 - C1 600
1546.043 - C1 - 10500
1546.092 - C1 - 10500
1546.108 - C5 - 10500
1546.122 - C5 - 10500

 

[n5pwp]

You only receive one 1200 Bd signal because they only transmit only one and have for some time.

Note many aero frequencies are spot rather than global beams. Some think frequencies have changed when they discover a spot beam they had not noticed before.

I went back and checked my SDR Receiver ini file and you're right about the 1200 Bd signal but that was not the point. My comment about the 1200 was that I thought I had read that they transmitted with more power which might explain why I was still getting it. My issue is that last year I received the 600 Bd signals fine and even some 10500. But this year they seem to be distorted and weaker. something has changed. I know there is some precession in the satellites throughout the day. My 10500 signals have always come and gone at different times of the day. I wonder if the patch antenna is sensitive to being mis-aligned by skew? I have the az and el set according to the satellite aiming software but I wonder if I may need to tweak the skew? I know, the real answer is to get a circular polarized antenna to really fix it. I just noticed that something had changed from what I was getting before.

Mike

 

[Hutchp]

Thanks Hutch.
You also mention a reduction in 600bps on Alphasat but i'm still seeing the same amount there was a good couple of months ago??
The only change i have noticed is the signal strength with the C1/C5 channels. I'm i missing something obvious here?

For context this what i monitor and still see as of today

90 GES
1545.115 - 600
1545.120 - 600
1545.125 - 1200
1545.130 - 600
1546.013 - 10500
1546.027 - 10500

C1/C5 GES
1545.160 - C5 600
1545.165 - C5 600
1545.185 - C5 600
1545.190 - C5 600
1545.215 - C1 600
1545.220 - C1 600
1545.225 - C1 600
1546.043 - C1 - 10500
1546.092 - C1 - 10500
1546.108 - C5 - 10500
1546.122 - C5 - 10500

Ok that's really interesting. So I think around end of May I was receiving all the channels you list, GES90 and C1/C5. Signal strength on all channels was excellent ( all 600bps at 50dB, 10500 channels at 20dB ) Then it looks like all C1/C5 channels dropped off completely. Just re-checked now. If I really look closely potentially they are there just at the noise floor. I am using a 1m antenna and haven't tried a re-point to look for them. Wonder if they have been moved into a spot beam? It just seemed co-incident with a drop of of USAFE traffic at the same time. I have another dish so I may try and re-point it to see if I can peak up on the C1/C5 channels. What size antenna /type are you using and what signal strength are you getting on the C1/C5 channels.

 

[Dark_sky]

Ok that's really interesting. So I think around end of May I was receiving all the channels you list, GES90 and C1/C5. Signal strength on all channels was excellent ( all 600bps at 50dB, 10500 channels at 20dB ) Then it looks like all C1/C5 channels dropped off completely. Just re-checked now. If I really look closely potentially they are there just at the noise floor. I am using a 1m antenna and haven't tried a re-point to look for them. Wonder if they have been moved into a spot beam? It just seemed co-incident with a drop of of USAFE traffic at the same time. I have another dish so I may try and re-point it to see if I can peak up on the C1/C5 channels. What size antenna /type are you using and what signal strength are you getting on the C1/C5 channels.

Thats strange your not seeing them Hutch considering you have a great setup, maybe re-pointing will find them. Using a SDR V3 patch antenna this end. Currently C1/C5 channels for 600bps are 13db 10500 2/4db. 10500 channels seem a bit sporadic - one moment they will be steady at 4db then suddenly drop to 2db. For voice had two of the Mildenhall tankers call up this morning on 25E so seems they are still using 25E for voice if they initiate to this GES. Really can't work out why C1/C5 are so weak?

To add to this rotated the antenna round to 90° E from 148° E and pulling in the C1/C5 channels slightly stronger - 10500bps up from 3db to 5db - slight improvement and able to just about decode.

 

[tsimola]

Hi,
First time poster here. I have 64cm offset pointed at Alphasat. I also noticed disappearance of C1/C5 channels couple of months ago, when someone noted it in a discussion group elsewhere on the internet. 90GES is still strong.

Actually, C1/C5 channels are there, but very very weak. Undecodeable on Jaero.

My location: Finland.

Cheers,
Tomi

 

[dlwtrunked]

I went back and checked my SDR Receiver ini file and you're right about the 1200 Bd signal but that was not the point. My comment about the 1200 was that I thought I had read that they transmitted with more power which might explain why I was still getting it. My issue is that last year I received the 600 Bd signals fine and even some 10500. But this year they seem to be distorted and weaker. something has changed. I know there is some precession in the satellites throughout the day. My 10500 signals have always come and gone at different times of the day. I wonder if the patch antenna is sensitive to being mis-aligned by skew? I have the az and el set according to the satellite aiming software but I wonder if I may need to tweak the skew? I know, the real answer is to get a circular polarized antenna to really fix it. I just noticed that something had changed from what I was getting before.

Mike

Most circularized antennas for this are circularly polarized (often by cutting a corner off the patch) and I am assuming yours is. But something with gain would help. I use a surplussed L-band dish but even then, sometimes the signals will seem weak. A related link:

https://www.sjsu.edu/people/raymond.kwok/docs/project172/Evan%20Wahlin%20172%20Final%20Report.pdf

 

[Hutchp]

Thats strange your not seeing them Hutch considering you have a great setup, maybe re-pointing will find them. Using a SDR V3 patch antenna this end. Currently C1/C5 channels for 600bps are 13db 10500 2/4db. 10500 channels seem a bit sporadic - one moment they will be steady at 4db then suddenly drop to 2db. For voice had two of the Mildenhall tankers call up this morning on 25E so seems they are still using 25E for voice if they initiate to this GES. Really can't work out why C1/C5 are so weak?

To add to this rotated the antenna round to 90° E from 148° E and pulling in the C1/C5 channels slightly stronger - 10500bps up from 3db to 5db - slight improvement and able to just about decode.

Definitely been some kind re-config on the satellite. Your patch antenna will have a much wider beam-width ( but lower gain) than my 1m so that may be why you can still just about see them. Kind of indicates that they moved to a spot beam, can't think that they would have moved to another co-located sat. Actually if you are still getting decodes on 600bps it may be worth looking to see where these aircraft are as that may give in indication if they are all located say East or West. I am lucky to also have access to a 9.0m C band antenna so I had this tracking Alphasat today. Plenty of voice channel decodes but again only GES-90 Fucino Earth station access. No sign of C1/C5. If I get chance tomorrow I will re-point a spare 1m and see if I can peak up on where the C1/C5 carriers are.

Hutch

 

[n5pwp]

But something with gain would help. A related link:

https://www.sjsu.edu/people/raymond.kwok/docs/project172/Evan%20Wahlin%20172%20Final%20Report.pdf

Thanks for the link. I gleaned what I could from it but most of it was beyond me. Your comment about something with gain is understandable in a perfect world. But my point was that something has changed. Last year and the years before I was able to keep a dozen streams going with no issue. This year something changed. I fired up TeamViewer and went out to check that my alignment was still good. I adjusted the patch in elevation and azimuth as well as skew and I could make the received signals weaker but not stronger. I checked your latest frequency list and went over my sdr_98W.ini file and the frequencies I have entered into it are all Global beams according to your list. So I don't know what has changed. I disconnected the coax connector and reseated it and nothing seems to improve it. The 600 Bd signals register on SDR-Receiver's power grid at about 20 - 22.5. The 1200 Bd signal is 30. The 10500Bd signals come in at 25 (but not locked).

I guess it may be time for me to move on to tracking something other than the ACARS signals on LBand. Its a mystery to me. Thanks for your suggestions though.

Mike

 

[Hutchp]

Hi,
First time poster here. I have 64cm offset pointed at Alphasat. I also noticed disappearance of C1/C5 channels couple of months ago, when someone noted it in a discussion group elsewhere on the internet. 90GES is still strong.

Actually, C1/C5 channels are there, but very very weak. Undecodeable on Jaero.

My location: Finland.

Cheers,
Tomi

Ok I think mystery solved. I just moved my spare 1m antenna around and was able to find the C1/C5 carriers all the way around East. So looks to me like they migrated to 62E or 64E, maybe I5-F1 or I4-F2. Can't get more accurate than that at the moment. I have a very poor look angle in that direction ( low elevation and through tree line) hence why they disappeared from my main antenna. I guess this maybe in preparation for the I6-F1 and I6-F2 satellites coming on line ? Maybe someone with a better look angle and higher elevation could confirm ?

Hutch

 

[Hutchp]

Looking at the Psmc channel I guess this must be 64.5E ( (SAT ID =3)which would fit with the Azimuth angle I have the antenna at.