Observation 8197315: UVSQ-SAT (47438)

Regarding Observation 8197315

Hey, everybody!

I noticed that my station does not decode signals with BPSK modulation.
And it does not decode either 9600 or 1200.
Can anyone tell me where to fix it?

When I replay the audio ogg file, I am able to decode the observation:

-> Packet from 9k6 BPSK downlink
    header = Container: 
        addresses = ListContainer: 
                callsign = u'LATMOS' (total 6)
                ssid = Container: 
                    ch = True
                    ssid = 0
                    extension = False
                callsign = u'LATMOS' (total 6)
                ssid = Container: 
                    ch = False
                    ssid = 1
                    extension = True
        control = 0x03
        pid = 0xF0
    info = b'\x08\x01\xc0\x00\x00" \x03\x19\x00\x00\x00\x028o\xdb*\x00\x00\x00\x16\x91F\xccaJ\x08?RI\xab\x88\xef\x98p\x00)\x85\xc0\x05u' (total 41)

Looking at the META data of the observation I see a couple of strange settings:

Assuming you are using a “standard” RTLSDR.

radio: {
name: "gr-satnogs",
version: "v2.3-compat-xxx-v2.3.4.0",
parameters: {
soapy-rx-device: "driver=rtlsdr",
samp-rate-rx: "2.048e6",
rx-freq: "437020000",
file-path: "/tmp/.satnogs/data/receiving_satnogs_8197315_2023-09-20T09-37-00.out",
waterfall-file-path: "/tmp/.satnogs/data/receiving_waterfall_8197315_2023-09-20T09-37-00.dat",
decoded-data-file-path: "/tmp/.satnogs/data/data_8197315",
doppler-correction-per-sec: null,
lo-offset: null,
ppm: "-115",
rigctl-port: "4532",
gain-mode: "Settings Field",
gain: "49",
antenna: "RX",
dev-args: null,
stream-args: null,
tune-args: null,
other-settings: "IF1=6,IF2=9,IF3=3,IF4=2,IF5=3,IF6=3,TUNER=52",
dc-removal: null,
bb-freq: null,
bw: "600e3",
enable-iq-dump: "0",
iq-file-path: null,
udp-dump-host: null,
udp-dump-port: 57356,
wpm: null,
baudrate: "9600",
framing: "ax25"
latitude: 50.359,
longitude: 30.388,
elevation: 200,
frequency: 437020000

One shouldn’t use gain-mode: "Settings Field", with a RTL-SDR and gain: "49", isn’t a supported value.

Gain mode should be set to Overall

And these are the supported RTL-SDR gain values:

Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6

If these are responsible for not decoding the data, I am not sure but one could start by changing these values.

Can you also provide some details on the hardware used, maybe that can help finding the source of this behavior.

Thanks for answer!

You are right, I am currently using the RTL SDR, but the version is one of the first, still on the E4000 chip.
So I set it up according to the instructions Software Defined Radio - SatNOGS Wiki
As far as I understood, the Gain value: is not used in this case.
But I’ll try changing that value and see what happens.

1 Like

Unfortunately, changing the gain level did not lead to a positive result.
The BPSK decoder still does not work on my station.
I’m using a Raspberry Pi 4b with 8 Gb of memory.
I used the following image to deploy the station:
Raspbian SatNOGS Image: artifacts.zip (Release: 2022091000)
Another example of observing BPSK mode at 1200 speed

Specifically the bpsk flowgraph isn’t performing very well, a few stations are using gr_satellites to do these and others. If you see frames that has _g0 etc in the filename this is from such a setup.
The waterfall looks kind of dark, do you use manual setting ? I think the default settings works best in my experience.

Is there any way to fix this? Maybe something to update?
Or will only installing from scratch help?

You are correct, I use the manual settings. With them the signals are more contrasty than with default settings and it is more convenient for me to see the presence of signals visually.
Does it affect the quality of reception?

Regarding bpsk, no reinstall will change that, it’s something inside the flowgraph and noone has yet fixed it.

Waterfall settings are not affecting demod nor audio. it’s just that when I vet a lot of different stations and occasionally come across one that has the waterfall gain set, it becomes a bit harder to evaluate. it is very easy to loose dynamic range, especially if other settings or hardware change/deteriorate.