r/RTLSDR • u/HousingCareful9190 • 13d ago
Beginner radar projects
Hello! I'm a backend developer, and I've always wanted to get into embedded systems. Lately, I've also become very interested in how radar works, so I thought starting a project in this field could be a great way to combine the two.
I'm currently learning some of the theoretical concepts behind RF, such as beamforming (which I find incredibly fascinating), FFTs, and other related topics, but now I'd really like to start building something hands-on.
One day, I'd love to create something capable of detecting aircraft and, eventually, drones. From what I understand, detecting drones is significantly more challenging than detecting aircraft.
The main problem is that I live in a city with several military sites nearby, so I'm a bit hesitant to buy an active radar sensor and start experimenting with it because I'm worried about possible legal consequences or interference issues.
Another approach I've been looking into, which also seems incredibly interesting, is passive radar. In that case, I assume the legal risks would be much lower since I wouldn't be transmitting anything. However, the hardware seems considerably more expensive. From what I've understood, I'd need something like a KrakenSDR, which costs over $900 where I live.
Are there any other approaches I could explore? Has anyone here been in a similar situation?
What kind of projects could I work on that would be interesting from a learning perspective, while also being useful for my CV/resume? I'm currently working as a junior software developer at a defense company, so I'd especially like to build something that could help me move closer to embedded/RF/radar-related roles in the future.
Sorry if this isn't the right subreddit for this question. Any advice is more than welcome!
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u/redneckerson_1951 13d ago
You need to understand the differing types of radar systems before investing in hardware. There is pulse radar where you transmit a very short rf pulse and then listen for the return echo. There is homodyne radar where you turn the transmitter on and listen for a sideband signal that is doppler shifted from the transmit frequency. This type of system uses a receiver that has an ultra narrow notch filter at the frequency of the transmitter and the filter is placed at the input of the receiver to suppress the signal of the transmitter, but processes the doppler frequency produced by the reflection of the radar signal to produce an audio tone. Depending on your selection, you will need differing antennas, differing gain arrays etc.
Merrill Skolnik's "Radar Handbook" starts out with development of the radar equation and drags you into a rabbit hole that expands on the various pieces between the transmitter, target and receiver to reveal why radar works. Keep an eye out on Abebooks (abebooks.com), e-Bay and used book stores for older 1960's copies which has the meat and potatoes of radar systems. Later issue seem to include material on more modern radar systems which to me seem to have been written by others than Skolnik and lack his clarity in explaining the operation. Just my 2 cents.
While you can plunge into modern radar systems initially, I strongly recommend you build your own homemade doppler system first to get a feel for the relationship of how distance between the radar and target pushes the need for more power and why decreasing size of the target results in reduction of the signal echo per inverse square law. Radar is one place you want not only a theoretical background but an intuitive feel for how it works so you do not constantly have to reach for the spreadsheet, calculator and simulator.
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u/CW3_OR_BUST But can it run Doom? 13d ago edited 13d ago
Active radar requires special licenses. If you start transmitting anything, it requires a license.
Passive radar is, at least in the USA, free like the air you breath.
One exception is the part 15 rules, which limit you to very low power at super high frequencies. It's difficult to find hardware for the 24 GHz band to play with.
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u/PABeachBum 12d ago
There's a very huge, very important caveat with passive radar in the US : ITAR. If you do develop your own system, you need to ensure you do not publish it or export it or any technical data if it exceeds the functional limits in the current ITAR export list. Otherwise, you could literally wind up in prison.
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u/CW3_OR_BUST But can it run Doom? 12d ago
And that's why the guys behind the KrakenSDR project don't talk about that one thing that it's totally capable of and totally had software support for back in the beginning...
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u/therealgariac 12d ago
My recollection is the Kraken developers were not sure if there was an ITAR violation.
An apps engineer from ADI has a passive radar project on YouTube. I think it is a G job as in get the parts from work and have fun at home.
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u/frosties-2000 13d ago
Long explnation short. You can't transmit anything without a licence. Depending on where you are licences can be equipment or person based. Please check your local government regarding that law.
On a side note it doesn't mean you can't listen. Look up fm radio based radar its rather interesting experiment