Daniel Estévez is an amateur radio operator and engineer who decodes signals from spacecraft and satellites using GNU Radio and software-defined radio.
Commenters recommend his work as fascinating and excellent, especially the Voyager 1 decoding series and his 802.11ah decoding post.
There are normally at least two radio links: telemetry and telecommand. Some spacecraft have multiple of each, with at least one channel of each being some sort of emergency channel where you can only do the most basic ops or get the most basic data.
As the sibling comment mentions, command signals are normally at least signed, and many times also encrypted.
Telemetry is way less sensitive, so it is usually not encrypted in scientific missions. There are well known protocols for space communications (e.g. CCSDS, PUS), so once you figure out a few fields you can make educated guesses of what each byte is. A previous post of the linked blog discusses it in detail: https://destevez.net/2020/08/tianwen-1-telemetry-framing-and-data/
Even without the actual telemetry, there are many things you can guess about the satellite attitude from just observing the radio signal. Many satellite and radio amateurs love doing that!
One thing that seems missing to me is that while the probe might send 160 bits/sec of useful data, those bits are not sent directly as such[1]:
The TMU encodes the high rate data stream with a convolutional code having constraint length of 7 and a symbol rate equal to twice the bit rate (k=7, r=1/2).
So the effective symbol rate is 320 baud[2], and thus a factor of two should be included in the calculations from what I can gather.
Note that the error correction was changed after Jupiter to use Reed-Solomon[3] (255,223) to lower the effective bit error rate, so effectively I guess the data rate is more like 140 bps.
[1]: https://web.archive.org/web/20130215195832/http://descanso.jpl.nasa.gov/DPSummary/Descanso4--Voyager_new.pdf
[2]: https://destevez.net/2021/09/decoding-voyager-1/
[3]: https://destevez.net/2021/12/voyager-1-and-reed-solomon/
Not sure about a mission as old as voyager, but most modern missions use CCSDS protocols, which are open and available online.
But just because you know the protocol dues not mean you have enough information to send a valid command. The commands are wrapped in a common protocol, but the commands themselves are typically mission-specific and definitely not made public.
Here’s an example of someone unaffiliated with the mission decoding JWST telemetry. While they were able to identify the packets defined per CCSDS protocols, they do not know the actual content of the packets, which are mission specific.
https://destevez.net/2021/12/decoding-james-webb-space-telescope/
And as someone else mentioned, the biggest hurdle with getting a command to voyager is access to a 70 m dish. Not many of those floating around…
Not necessarily leading-edge stuff, but the work he did on Voyager 1 decoding with GNU Radio was fascinating (e.g. https://destevez.net/2021/09/decoding-voyager-1/ ). Same with 802.11ah ( https://destevez.net/2025/01/decoding-ieee-802-11ah/ ). The fact that he puts so much care and attention into describing the methodology as well as the results makes his blog a great educational resource for GNU Radio and communications DSP in general.
Estevez pretty much does for DSP what Karpathy does for ML, sans the latter's videos.
I also just noticed a post on the Remez algorithm for FIR filter design, where he ran into some of the same problems with 1970s-era legacy code that I have and (unlike me) actually addressed them. That one, I'm going to have to bookmark for sure.
Another interesting possibility is to use GPS for a clock. [1] Apparently 1 microsecond accuracy. Maybe useful if you want to make the distance really far. Someone has an article [2] Would be cool if you could pool the resources of multiple amateur rigs over a great distance in ad hoc antenna arrays.
[1] https://digitaldisplay.com/network-clock/master-clock/gps-vs-ntp-master-clock/#:~:text=GPS%20accuracy%20is%20~%201%20microsecond,less%20latency%20compared%20to%20NTP.&text=clear%20sky%2C%20and%20after%20satellites,second%20to%20the%20slave%20clocks.
[2]https://destevez.net/2022/03/timing-sdr-recordings-with-gps/
Daniel Estévez (https://destevez.net/) has lots of interesting blog posts on using tools like GNU Radio and Jupiter to decode transmissions from various objects in space. He's recently also been looking at LTE.
I would also recommend CuriousMarc who has done a lot of work with his friends on restoring some radio equipment from the Apollo missions: https://www.youtube.com/watch?v=v49ucdZcx9s&list=PL-_93BVApb58SXL-BCv4rVHL-8GuC2WGb
There are lots of good explanations of the how and why in those videos.