Receiving Shields-1

Satellites & Observations
1

I was looking at the most inexpensive way to listen to shields-1. I notice a whole lot of good reports with signal in the -70dBm range from people using inexpensive turnstiles or other omnidirectional antennas. With a vertically polarized whip antenna here in Virginia I am seeing no higher than -120dBm on various passes (whip antenna going into a boatanchor R-1283 receiver with good calibration). Is the improvement with the properly polarized turnstile or quadrifilar that much better? Or am I instead just testing on passes that are too low to the horizon?

I am familiar with the 1200bps FSK which requires relatively low S/N to get good data… just how much worse is Mode U format? How much signal should I need to expect before I can get solid copy?

Guys like @Jim look like they are getting beautiful observations… Jim, what exactly is your receiver setup? You say you have a SAW filter and preamp in front of the SDA… what are they? Are you able to consistently receive whenever it’s over the radio horizon?

As you can tell, I don’t know much about satellites. I am just an HF guy who got very curious.

2

So… followon… I have an omni antenna, a homebrew preselector and preamp going into an SDR supported with gqrx and I can pull a noisy audio file with narrowband FM demodulation… don’t get full FM quieting, but I get clear audio. So… now what do I need to be doing in order to take this .wav file containing FM-demodulated 9600 bps FSK audio and turn it into a data file?

3

quick answer on the demodulation, it’s ax.25 g3ruh, so anything able to read wav and demod should do.
my preference is gr_satellies, others use soundmodem, also direwolf, probably many more available.
gr-satellites does not have many of the 400MHz satellites in it’s collection, but you can choose any of them that is supported and use that same mode ax.25 g3ruh instead.

for example, using obs 12082722 audio, and gr-satellites version 5.8 (any 3.x version you need to convert ogg to wav first):
gr_satellites acrux-1 --wavfile satnogs_12082722_2025-08-02T02-42-07.ogg

-> Packet from 9k6 FSK downlink
Container:
    header = Container:
        addresses = ListContainer:
            Container:
                callsign = u'SHIELD' (total 6)
                ssid = Container:
                    ch = False
                    ssid = 0
                    extension = False
            Container:
                callsign = u'CQ' (total 2)
                ssid = Container:
                    ch = True
                    ssid = 0
                    extension = True
        control = 0x03
        pid = 0xF0
    info = b"\xab\xcd\x00\x00\x00\x00\x00\xc9\x00C\x0b\x01\x00\xae\xff\x96\xd2\x04\x00\x02\x1f\x00\xff\x05\x8c\x00\xfeo\x00\xee\x01\x96\xd2\x04\x00\xbc\xf4\xe9C\x00\x00\x01\x00\x00\xff\xe8\x03\xf0U\x0e\x00\xe9\x04i\x01\xdd\x0c\x06\x00\x01\x00\x1e\x00\x1a\x00\x03\x00\x02\x00\x03\x00\x02\x00K)\x00\x00\xb8r\x02xo#\x00\x00[\xba\x11\x00\x8b\x01\xda\x00F\n\xa4\n\xc4\t\x02\r\x8f\x06\x8f\x06\x92\x06\x95\x06.\x000\x00\x00\rr\x06\x13\x00\x1c\x00Q\rd\x06H\x08\x88\x06D\x08N\x00`\x0b!\x00r\x0bM\x03\x1e\x0f\xcf\x01T\x06\x16\x0f?\x01I\x068\x01y\x0e\xff\x00\xff\x00\xff\x00\xff\x00\xff\x00\xff\x00\xff\x00\xff\x00\x00\x00]\xde*\x00\t\x06\x06\x00\x00#\x00\xff\xd0\x07:,\x0b\x00\x00\x00#\xc9\xd0'\x0b\x00" (total 201)
2 Likes
4

Thanks for the help! I’m using an RHCP QFH antenna and getting a signal but a very weak one… should I in fact have got the antenna set up for LHCP instead? Nobody seems to know.

Incidentally the satellite is not sending the beacon right now but just replies to interrogations so there isn’t as much to see this week as normal.

1 Like
5

voila. i try this tips for lapan-a2 (io86) and it work flawless. lapan-a2 not officially listed by gr-satellites, but its aprs use same ax.25 1k2 afsk modulation, that many satellites in gr_satellites supported page using this method, example: bricsat-2, cape-3, etc.

make sense when i join the umka-1 racing event, the umka-1 can decoded too using vizard-meteo on gr_satellites

from this obs

gr_satellites bricsat-2 --wavfile satnogs_12762939_2025-11-19T14-04-36.ogg 
-> Packet from 1k2 AFSK downlink
Container: 
    header = Container: 
        addresses = ListContainer: 
            Container: 
                callsign = u'APOT21' (total 6)
                ssid = Container: 
                    ch = True
                    ssid = 0
                    extension = False
            Container: 
                callsign = u'YB0X' (total 4)
                ssid = Container: 
                    ch = True
                    ssid = 1
                    extension = False
            Container: 
                callsign = u'SGATE' (total 5)
                ssid = Container: 
                    ch = False
                    ssid = 0
                    extension = True
        control = 0x03
        pid = 0xF0
    info = b'>  4C Bravo Satelit Indonesia' (total 29)