Alphasat weak Signal / Satellite problem (Problem confirmed)

Hello, i read that there was only a weak Signal from Alphasat for the last few days.

I also got almoast no Signal until yesterday. Today i got up to 7,5db SNR, what was as strong as never before.
Now the signal is down to around 2,2db SNR, without even touching my receiver. The weather is also nice and sunny.

Has anyone the same Issue?

It would also be great if some one from Outernet could confirm if there is a satellite problem or not :slight_smile:

Greetings from Cologne / Germany

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Hi Tysonpower,
i am near you and receiving with 4 bars (abt. 8dB SNR) like usual, local time now 17:20.
Wolfgang

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Hi Wolfgang,
i adjusted my Antenna a little bit so it is pointed directly at the satellite. Now i get about 3-4db SNR, but not very consistent. Its jumping around between high twos and low fours.

Is your Receiver indoor or Outdoor? My Antenna is only pointing out the Window.

UPDATE [20:40 UTC] : Receiver was not touched. SNR only 1,5 to 2,5db. Angle is right, CHIP reboot also does not change anything. What?

regards, Manuel

We are definitely experiencing anomalies in Alphasat. I’ll be talking to the operator about this next week.

Thank you for the reply.

My Signal is between 4-5,5db SNR at the moment (7:00 UTC).

@Syed Can you update us in this thread if you got some information from Alphasat? Thanks!

regards, Manuel

hello Manuel, I am receiving with 4 bars (8dB SNR) at the moment. To compare, you can visit obereip.selfhost.de . The hardware difference to your setup is, that I am using a Raspberry Pi and Librarian. I never got the CHIP running stable. If you have a RPI laying around, perhaps try it. My complete setup is outdoor and sits in a Tupperbox. It looks to 155° and 30° up with free view to the Alphasat. For the setup I used dishpointer.com to find the line of sight between to uphill neighbours.
Wolfgang

Hello Wolfgang, thank you for the information about your setup :slight_smile: very interesting.

As i mentiond before, my Antnna is indoors at a Window. I think that your Signal is so strong that the SDR can compensate with the internal gain for the anomalies of Alphasat. If my receiver has not been touched, but the SNR changes, it can only be the Signal from the sat that changes in my opinion.

My CHIP works great so far on Librarian. The only thing to note, is that you can’t plugin the SDR directly into the CHIP because the Heat of the SDR is transferred into the CHIP. Then it shutsdown all 3h or so :open_mouth:

regards, Manuel

I have seen extreme variations ( down to almost no signal at all) over the last Month or so on Alphasat.
At one stage I had to turn my patch antenna 90 degrees to get any signal, which made me think that there is a signal polarity issue from the bird…
I am not plotting the signal , and I am away at the moment, so I can’t watch it all the time…

there is definitely an issue with the signal from Alphasat.

We are still tracing where it is though :expressionless:

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Okay. Please keep us updatet if you found the reason of the low Signal from Alphasat.

Just as a status from my Receiver (does something like that help you?)

6:00 UTC - 4,5-5 db SNR
11:00 UTC - 3-4 db SNR
14:00 UTC - 3-3,5 db SNR
21:00 UTC - 0-2 db SNR

Can it be the case, that the sat is out of sync with the roation of the Earth or so? because the Signal gets lower from morning to evening. Ir could lead to wrong polarization. Just a guess :slight_smile:

regards, Manuel

It’s a geostationary satellite, so hopefully stabilized and not rotating :slight_smile:

some SNR fluctuation is normal because the signal travels 36000 km:
http://www.mpoweruk.com/satellites.htm

I use a 6 inch USB cable between the two and it acts as a heat isolator. The chip runs much better.

I have the RTL-SDR.COM stick (i.e. not the one shown on most photographs) and while it gets a
little warm, it gets nowhere near temperatures that would cause any issues with a microprocessor.
It currently sits at the window sill in an unheated room (maybe 16-18 deg C there), and it may get
to 25 deg C or so. The CHIP has never crashed without other explanation.

Yes Zoltan, that is true, and that I expect…
I don’t expect it to go from 7db to 2db in a few minutes though and stay they until I actually rotate the antenna when it come back to about 4 or 5db.
When I did this , I move the location of that patch re pointed and angled etc,. etc. etc. before trying to rotate it by 90Degrees
I am now back at the location of the system, it has bee keeping a signal all week., currently just making 3db under clear skies with the cable from the antenna coming out of the top :slight_smile:

@Mudflap @pe1chl i also use a very short USB cable with the RTL-SDR.com v3, because the CHIP will shutdown after some hours, as mentioned before. My SDR only warms up to around 33°C, even if the Sun shines on it, like it is at the moment.

@zoltan I know that the sats are around 36000km away and that the signal will fluctuate because of that. But it should not be so extreme. i think rotating could lead to something like that, but that would be realy bad :slight_smile:

@neil that is very strange…i hope that outernet get’s information about the problem from the operator of Alphasat.

Just as a short status update:

9:00 UTC - 4,5-5 db SNR
10:UTC - 1,5-2 db SNR
10:45 UTC - 2,2-3 db SNR

It was confirmed twice from outernet, that Alphasat has a problem. The only question now is what is causing it. :neutral_face:

Yeah - I am just sad that this is holding up the bugfix update of Skylark.
I am really hoping to see how the “over the air” update goes :slight_smile:

Speaking of OTA updates, @Abhishek , what will we see in Skylark that tells us an update occurred?? Ken

thats a good question. I had been planning to make a post about it a day before sending out the OTA. Let me do that now - no need to hold off of that information.

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Just for the record…
at 21:06 GMT … NOTHING in my setup has changed but I am getting ZERO signal from Alphasat
This is what I have see before too…
The sky is 100% clear too
I can almost guarantee you that if I go and TURN the patch ant 90 degrees I will get 3db or so from it until it changes again at some time…
I am not going to change anything at all though - it has been in th same place all week
You can see from the screen shot that the last info was at 19:21GMT

Neil, although we have also seen the positive effect of rotating the patch antenna (a few months ago played with that) theoretically this shouldn’t introduce any change as the polarization is right hand circular (RHCP) so rotation doesn’t effect the reception. Maybe what causing some change is the effect of the coaxial cable GND skirt hanging around and influencing the main lobe a bit (just thinking aloud… I’m often designing antennas and when measured on VNA the effect of the measure coaxial pigtail can be seen for example)

If my above assumption is good then you might have local EMI issues (for example I have extremely strong from EU LTE base stations possibly…so had to play with antenna orientation a lot to find a good place here).

Can you make a logging script of your SNR and RSSI levels (and perhaps the frequency offset too) with UTC time stamps for debugging?

Thanks,
Zoltan