PW-Sat2 Telemetry decoder


#1

Previously we’ve discussed some issues and challenges concerning SatNOGS telemetry decoder for PW-Sat2 satellite in general SSO-A topic.

I’d like to sum up some important information about PW-Sat2 satellite:

The goal is to prepare reliable BPSK demodulator (I heard about not sufficient tests for 9k6) and telemetry decoder :slight_smile:

If I missed something - just ask, I’m here to answer.

Cheers,
Michal


#2

I had success with our own generic BPSK demodulator with all of your recordings. I am in the process of comparing your and also in lower SNRs.


#3

@begreen pointed out the LE issue we also have on FOX-satellites, so it might turn out to be as complicated in satnogs-decoders. We need to find a solution for that…


#4

@surligas “demodulated” the iq recordings provided on @begreen’s website.
They are only containing a “dummy periodic message”, but this shows the whole decoding process works.
The only thing to do is now: clear the LE issue for data values!


#5

@DL4PD Maybe you’ve missed it - I also provided the IQ file with real telemetry (not only “dummy” frames): http://collectd.titan.gajoch.pl/recordings/session_4_1200.iq It can be helpful for testing purposes :slight_smile:

I’m happy to see that BPSK demod works as expected :smiley:


#6

Let me see if I can demodulate them myself - I just got some frames from @surligas to play with…


#7

Thanks for first decoded frames - https://network.satnogs.org/observations/349712/
I’ve downloaded those 3 frames and uploaded to our parser:


#8

Hah! That are live frames to test my decoder struct against :wink:


#9

By the way - do you know why only one observation (here) contains decoded data? Others look also promising but lack of incomplete/not decoded data sets?


#10

I didn’t check all, but: there are a lot of obs with very faint signals. The one that decodes curiously decoded with an old (and very simple compared to the new one) version of the BPSK decoder (basically the one I developed for PICSAT some time ago).
Maybe we should try to capture some IQs to get @surligas into this :wink:


#11

There is perhaps an issue for small baudrates, due to a fixed non-parametric transition width at the low pass filter. An IQ recording will help to fix that!


#12

I have IQ recording of this: https://network.satnogs.org/observations/350783/
Can you use it?


#13

Yes! Upload it if you can.


#14

@csete - I’m also interested! :slight_smile: I’ll put it to our demodulator.


#15

@surligas Done.

@begreen I will send you a PM with the link.


#16

We’ve decided to stay on BPSK 9k6 for most of the time. We’ve finished commissioning of the satellite and now entering experiments phase, so we’ll demand more energy and higher baud rate is one of the energy-saving method.

Find out more:


#17

Hi!
I think that we should remove 1k2, 2k4, 4k8 bps modes from the list - we’re using and will be using in the future 9k6 only.

Another topic that I’d like to discuss is data demodulation - 99,99% observations are useless for now, because the only output is a waterfall. There are no demod data, moreover it’s impossible to demod 9k6 data from ogg file (because of this problem: Ogg artifacts frequency offset).

In our software/webapp dedicated to mission there are right now 377006 frames received and uploaded, so I’m wondering what’s the problem with SatNOGS. So I’d like to solve it and get similar demoded amount of data in the future from satnogs :wink:


#18

Hey,
There is no flowgraph to demodulate in gr-satnogs yet. Maybe you could contribute one? :slight_smile:
I do also have a katai struct decoder laying around I need to do some checks, maybe a refactor with it.

db.satnogs.org is holding something around 30k frames for PW-Sat2…

Give me a ping - I’m always happy to help!


#19

According to:

I must have been wrong! Maybe there is an issue with SNR or something, so still your contribution would be awesome!


#20

Yes, that’s true adn great! But I believe that could be much more - most of the observations lack demod data. I think I can try to adapt our (PW-Sat2) GRC flow graphs that we use to demodulate BPSK and decode AX.25. But it demands some cleaning :smiley: Maybe you’ve already taken a look at this flowgraph and can comment if you think it’s worth to use it?

Concerning your katai struct decoder - I remember that there was an issue with bit endianness (because of lack of kaitai support). Is that resolved now? Another thing is that we’ve updated on-board software introducing a new power saving mode, so there is additional ‘short’ telemetry frame format :smile: However it’s much easier than ‘full telemetry’ frame.

But the first thing I’d like to take up is to figure out and fix (if possible, maybe it’s SNR issue) observations without data.

Thanks for your help @DL4PD!

BTW. Is there any API or sth like this to access data in SatNOGS db in real-time? I know that there is an option to download data in csv but having it in real time would be great!