I have a lot of problems trying to decode Russian cubesat TM using HS Modem! Yes, I have successfully decoded data from UMKA-1, Vizard-Meteo etc, BUT… it seems very hit and miss if it’s actually going to decode or not.
I’m not talking about weak TM signals. I record the strongest data bursts in SDR# and then play them back into HS Modem. If it decodes these into hex code, then I can use the relevant decoder to display the TM data.
But does anyone have tips as to how to get this modem to decode ‘reliably’? For example, I’m using hs_soundmodem from the UMKA-1 TM decoder Windows 64 zip file. I set the baud rate to GMSK 4800, select the input channel (usually I play the audio file back into Virtual Audio Cable).
How about the DCD threshold setting? I have had more success by installing FXSound app and then setting the latter to maximum volume on all frequency bands and piping my TM audio file via FXSound app and then into HS Modem app.
I’m sure HS Modem is a great piece of software. But it only works for me maybe 10% of the time, which means that I have many TM files that I can;t decode
HS modem seems to be a bit finicky about volume at my end. Too little and too much and it wont decode.
Whenever i have problems i record a couple of packets to a audio file and play it back in loop using VLC and gradually adjust the volume until it decodes. You can change the audio device under “Audio” in VLC.
Ofcourse any kind of low/high pass filter will result in no decode.
UZ7HO started with only two soundmodems that where able to decode AFSK 1k2 AX.25 and G3RUH 9k6 AX.25, this made it possible to run Packet radio without expensive hardware modems.
The AFSK 1k2 version is just called soundmodem
And the G3RUH version is called hs_soundmodem
I don’t know where the cooperation started, but UZ7HO started to support us satellites enthusiast, and this is far before networks like SatNOGS or tools like GNURadio and or gr-satellites existed.
At first code was added to the existing versions as you can see when selecting the left top pull down
When modulation and decoding schemes got more complicated the name stayed but with new support, there we saw the first others version.
So currently almost all versions are called hs_soundmodem.exe but are specific for a satellite or a decode technology.
For example the latest Russian satellites use an USP de-framer, so there you need to use the hs_soundmodem version that is specific for that technology.
Start with downloading the basic and others version and go from there, in the meantime there are a lot version available. Below a short list.
Let me start by mentioning “Use the operating system that feeds your needs”
And at the same time if you like a challenge and love to work with bolts, nuts and washers and you have a big toolbox, then *nix is a great operating system and you will enjoy it.
So it all comes down to, do you like to go to a command line and execute code and try to connect output and input to get a result.
It can be a steep learning curve, one of my old mentors (1988) told me, *nix does nothing until you tell it to.
That sounded strange at the time until I experienced that I had the configure the whole input output chain.
Source is SDR++ v1.1.0 that is piped through virtual cable to HS modem.
If its recorded then its 16 bit wav 44.1khz recorded with SDR++ audio recorder. HS modem is set to 44100khz samplerate.
I have loaded these wav files into Audacity and there is no clipping.
I have not tried any other SDR software so it might be something iffy with SDR++. Its also a rather old version. Might also be some windows setting, or the integral sound card on this Lenovo laptop.
In general make sure there is no audio filtering enabled, from experience I know that it makes the bandwidth smaller and then there isn’t enough information send to the soundmodem.
