Observation 800967: PSAT-2 (99969)


#1

Regarding Observation 800967
Is it possible to make some kind of frequency calibration at this station? It has one of strongest spectrograms, but 12kHz offset from the center frequency. Then in demodulated audio is no signal. Thank you.


#2

It’s not an issue of the station but the UHF SSTV transmitter of PSAT-2 drifts a lot… not sure why. Many times you can see it drift during the transmission too. PSAT-2 on VHF works fine.

Check other observations from this station, like this one and you’ll see that the signal is centered correctly.


#3

The observation you linked from that station is of CP9, not PSAT-2.

That station has observed PSAT-2, with a frequency offset: https://network.satnogs.org/observations/800969/

My home station observed PSAT-2 this morning, with an even bigger offset: https://network.satnogs.org/observations/807051/

The best I’ve found in recent days is this one, which appears to be right down the middle: https://network.satnogs.org/observations/800441/

It’s a bit of a shame, as those recent passes had very strong signal, but the frequency offset has made it not possible to decode the SSTV imagery.

I have noticed that the offset seems to be pretty consistently present over the Australian stations…


#4

“the frequency offset has made it not possible to decode the SSTV imagery.” That is why I always record the raw IQ also, although usually just go back and delete it a few days later. On these occasions it would be useful, and can share it if needed.


#5

Hai,

That’s my station, and yes the RTL-SDRs have been calibrated against the LTE network. PSAT-2 does drift often and I’ve much better success using the IQ samples. Network bandwidth is limited, but I’ve trying to get them uploaded to here -> here. I’ve had to disable it for a bit, but I’ll try letting it upload again for a couple of days.


#6

Oh that’s good - had to get my aws credentials out of mothballs but this works:
$ aws s3api get-object --bucket satnogs-iq --key 821782.raw 821782.raw

Did not know about that signal repo.


#7

grabbing the raw spectrum for 800969 and playing nfm to qsstv with offset recovered this image:
image


#8

There is also psk-31 telemetry in there, from 800969 and 800970 - can be decoded with utility here: https://github.com/alpov/PSAT-2

from 800970
upper freq
PSAT-2 A cnBr bBamkFuBppjyac aaaa A cmoy bBadkjvmpqjwad
later
PSAT-2 A cnBA bBadkyupppkdae daab A cmob bBapjsuxppkdac
lower freq
PSAT-2 S EzDD abefaaaa Cjalglarboctaa
later
PSAT-2 S EAdr acgwaaaa Cjalgoarboctaa

800969 lower freq
PSAT-2 S EzDD abefaaaa Cjalglarboctaa
later
PSAT-2 S EAdr acgwaaaa Cjalgoarboctaa
upper
PSAT-2 A cnBr bBamkFuBppjyac aaaa A cmoy bBadkjvmpqjwad
later
PSAT-2 A cnBA bBadkyupppkdae daab A cmob bBapjsuxppkdac


#9

Looks like the latest observations didn’t upload due to poor internet again :frowning:

wlan0     IEEE 802.11  ESSID:""  
          Mode:Managed  Frequency:2.412 GHz  Access Point:    
          Bit Rate=2 Mb/s   Tx-Power=31 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:on
          Link Quality=26/70  Signal level=-84 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:22460  Invalid misc:0   Missed beacon:0

I’m going to let them buffer on an external USB stick and they’ll retry to upload every observation. I’m not sure how well this will work though.


#10

Hi all, thank you for the raw archive available, we do not know the reason of the frequency drift, it is seen just over the VK stations, in Europe and US, it seems to be just above the frequency around 435.355MHz. Our receptions here are very spotty and any signal for us is valuable. Due to orbit character, in couple of days we will even have window of 11 days when no pass is occuring here. Tomas


#11

My Az/El station is now uploading observations to the same AWS bucket, so any future observations (starting from obs 831469 and up) from https://network.satnogs.org/observations/?station=232 should now be accessible in the same way (i.e. https://satnogs-iq.s3-ap-southeast-2.amazonaws.com/.raw )