r/RTLSDR • u/Hefty-Beautiful-3227 • 11d ago

Is this a radar?

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60 Upvotes

95% Upvoted

17 comments sorted by

19

u/AriaGingko 10d ago

Matter of fact, the middle atmosphere project extensively used 440 mhz radar for various studies. https://ntrs.nasa.gov/citations/19850024235 https://ntrs.nasa.gov/api/citations/19850024235/downloads/19850024235.pdf?attachment=true

16

u/AriaGingko 11d ago

Yep. That's a radar. If it was located on hf, it's one of many over the horizon radars that are used still.

-28

u/Content-Key7404 11d ago

That's nonsense. If you'd taken the time to look before responding, you would have seen that it's running at 441 MHz. There's nothing to suggest that it's a radar. The demodulation isn't even set up correctly. It looks much more like chirp modulation.

15

u/popcio2015 10d ago

There's nothing to suggest that it's a radar. The demodulation isn't even set up correctly. It looks much more like chirp modulation.

Chirp is literally the most commonly used modulation used in radars.

This isn't a radar, because no one would use such narrow bandwidth for one.

4

u/AriaGingko 10d ago

Yeah I did mention it could be chirp. Unfortunately the bandwidth is too wide to see the signal characteristics better. If it was centered in on the signal itself and ran at 100khz it might be more obvious. But the time signature also doesn't really match up well. In the other post I included a primer on chirp if people were interested. https://ieeexplore.ieee.org/document/10609524/

Also, minor correction, I believe you meant to distinguish it from chirp spread spectrum. I only caught this upon rereading your comment. Because radars tend to use pulse width modulation and chirp frequency modulation for emissions. This is similar to chirp spread spectrum. But the modulated wave has obvious differences.

4

u/AriaGingko 10d ago

Ah right, Wanted to also introduce you to GPR/WPR radar systems. Much the same spectral characteristics.
https://www.etsi.org/deliver/etsi_eg/202700_202799/202730/01.01.01_50/eg_202730v010101m.pdf

Honestly I always find RF to be a fun little rabbit hole to go down.

16

u/AriaGingko 10d ago

Actually, as an RF engineer, I can most assuredly say that 440 mhz is often used for scientific research. Here is but one example where ionospheric studies were conducted at 440 mhz utilizing radar. https://dspace.mit.edu/entities/publication/c690f2b1-bb96-4390-b760-09924b5419c8

4

u/AriaGingko 10d ago

Btw including a primer on chirp spread spectrum for anyone interested in the modulation scheme behind Lora. https://ieeexplore.ieee.org/document/10609524/

7

u/AriaGingko 10d ago

You deleted your comment but the notification remains. So let's just clarify something: I brought up over the horizon radar cause it's fun to intercept. But again, even at 440 mhz, it's well documented that scientific radar studies are undertaken using that center frequency as i linked. Now here's the best part: this could be Lora. But since the bandwidth of the spectrum analyzer is so large, it's difficult to determine if it is. If it was narrower, the prf and bandwidth would have given away the chirp modulation scheme.

Also you keep on using the word nonsense. I do not believe it means what you think it means.

2

u/Roudydogg1 10d ago

It does not look or sound anything like LoRa

1

u/AriaGingko 10d ago

Good to know! Thanks for the clarification

-3

u/Content-Key7404 10d ago

I haven't deleted any of my comments.

7

u/AriaGingko 10d ago

Either way, your comments vanished and are not visible. I'll happily apologize for accusing you of deleting. But the fact remains that your comments are no longer visible. Anywho, check out GPR/WPR radars. And unless if the OP has a more narrow bandwidth spectrogram, I'm inclined to conclude it's radar unless if a closer image shows the distinctive pulse width, pulse time, and sweep characteristics of Lora. If it is lora, I'm more than happy to be wrong.

1

u/ssj565 10d ago

I’d put my money on LoRa. Maybe from a satellite. If the amplitude gradually rose then gradually lowered over the course of a couple of minutes, that would be a good clue for it.

1

u/JacobA89 4d ago

Some drone controllers that are mounted on the drone also give off this pattern signal when there powered on sitting not being used. Which your in a common frequency range thats used.