Observation 11301385: METEOR M2-3 - unable to decode LRPT

As per the title, I’m not having much luck with LRPT decoding. Here’s the latest observation taken : Observation 11301385

Based on the waterfall, is this sufficient signal to get a workable image (even if it’s a tiny sliver of image)?

If so, do I need to bump up the gain or sample rate?

Or is it a config issue with the meteor_démod and meteor_decode tools used in the satnogs client?

I’ve also got the client to retain the IQ dumps and fed it into sat dump in the host system with this:

satdump meteor_m2-x_lrpt baseband $IQFILE ./ --samplerate 160000 --baseband_format f32 --freq_shift 137900000

Where IQFILE is the path to the raw iq file

I’d love to have the client upload demoded data, but at this point would be happy to figure out how to get any sort of image out of these observations.

Hi,

As LRPT is not supported natively by the -client and -flowgraphs it is a bit of a hassle to get it working.
My last attempt was this script and we made the “IQ recording” transmitter definitions to make the sample rate high enough, in this case 160ksps.
I don’t recall all the details, but there were at least two bitrates 72/80ksps and the interlace option and these changed constantly and it just had to match for any image to be produced. It also made the frequency change 137.9/137.5

The format of the IQ dump is s16 and not f32 so you need to change that in the satdump command line.
The freq_shift option should not be used either, this is only for tine tuning the center frequency, and in this case it is already at 0, and absolutely not 137.9MHz from the IQ files DC.

If you want to have a go at implementing the product upload (and it’s configuration json) with satdump, there’s this script that is the basics covered. You need to match another norad id and add the appropriate command line etc.

1 Like

Awesome, reading it as s16 did the trick. I also just realised that I need to select LRPT IQ Usage FSK, because my last observation was set to LRPT RHCP 7200 and the sample rate was too low for satdump to decode it

As for the satdump script, I’m certainly happy to put something together for posting demoded images when I get the time.

3 Likes