pommes
Newbie
- Joined
- Jan 31, 2025
- Messages
- 1
Hi, Im new to direction finding and radio topic in general. I got into it 6 months ago because Ive realized how much we are surrounded by the electromagnetic waves and how much a signal can tell. So now im here doing my bachelor project about RF data visualization in VR/AR and sound.
Background
So far I learned SDRs and played a lot with RTL-SDR. I also developed a mobile spectrum sonifier based on Raspberry Pi that does a sweep scan, compares the data with the frequency allocation database of my country and turns it into sound. I also did my research on spectrum scanning and direction finding. And I know how to code, so custom software is not a problem.
Objective
My goal is to create a mobile device (e.g. based on Raspberry Pi+SDR) that would DF incoming peaks in its (instantaneous) bandwidth in real time, and then display the directions+data around the user using VR/AR. The size should be portable and the user should be able to walk with it. And I want to be able to scan the whole possible spectrum range supported by the SDR (somewhere from 70MHz to 6GHz). The DF will be done in a busy urban environment. And of course my budget is limited to max 700$ for the whole technical part.
Questions
Which DF method should I choose? What equipment do I need?
My thoughts on this
I already know that there is no perfect solution to this problem, but I tried to develop some concepts that would meet my expectations.
So for SDR I would prefer Pluto+ SDR, its quite affordable (150-200$), has IBW of 20MHz and covers a range from 70MHz to 6GHz. I would like to have the directional antenna array as it makes the most sense in my head. But if that's not possible, I can't decide between Pseudo-Doppler and Correlative Interferometry, it depends on technical requirements, information accessibility and price. Is there a commonly used method that I have missed?
Thanks for your time and help!
Background
So far I learned SDRs and played a lot with RTL-SDR. I also developed a mobile spectrum sonifier based on Raspberry Pi that does a sweep scan, compares the data with the frequency allocation database of my country and turns it into sound. I also did my research on spectrum scanning and direction finding. And I know how to code, so custom software is not a problem.
Objective
My goal is to create a mobile device (e.g. based on Raspberry Pi+SDR) that would DF incoming peaks in its (instantaneous) bandwidth in real time, and then display the directions+data around the user using VR/AR. The size should be portable and the user should be able to walk with it. And I want to be able to scan the whole possible spectrum range supported by the SDR (somewhere from 70MHz to 6GHz). The DF will be done in a busy urban environment. And of course my budget is limited to max 700$ for the whole technical part.
Questions
Which DF method should I choose? What equipment do I need?
My thoughts on this
I already know that there is no perfect solution to this problem, but I tried to develop some concepts that would meet my expectations.
Pseudo-Doppler
HackRF+Opera Cake Switch with 4+ Antenna Array (Circular)Pluto+ SDR+Switch with 4+ Antenna Array (Circular)4+ RTLSDR working in sync
From my knowledge I could say that this is an easier solution for automatic DF, but it is not as good because of the multipath problem. Also, there is no need for coherent channels, so I do not need to spend my money on multichannel SDR or multiple SDRs.
Directional Antenna Array
SDR with directional Array (Linear/Matrix/Circular)
This would be a good solution since you can only look in one direction when wearing VR/AR. So mounting directional antennas directly on your headset would work for your field of view (or you could mount them around). The biggest problem is that wideband directional antennas are too big and expensive, but I've read about patch antenna arrays (that switch depending on the band), so maybe I could make custom PCBs with such an array and a switch (gets too complicated). Do you know of a directional antenna that is small enough? And is it mandatory that the channels are synchronized or can I just switch very fast between the antennas and lose some milliseconds?
Beamforming
4+ RTLSDR working in syncPluto+ SDR with 2 channel RX
The need to change the antenna spacing for different bands kills the mobility/portability. And I still do not fully understand the principle.
Correlative Interferometry
Pluto+ SDR with 2 channel RX (inaccurate)2 Pluto+ SDR with 2 channel RX in sync (4 channels totally)3+ RTL SDR working in sync
I think this is the most interesting method. The problem is that you need precise engineering and calibration to make it work. On the other hand, it's not affected by multipath as much as Doppler. So I've seen KrakenSDR and I know it uses this technique. It's great because you can find a lot of footage of it in action. And what I also found was this article by Epiq and Deepsig where they did PDoA with two antennas using ML. So I could imagine training a model for DF, but I do not have enough knowledge about the process behind it to actually create a dataset.
So for SDR I would prefer Pluto+ SDR, its quite affordable (150-200$), has IBW of 20MHz and covers a range from 70MHz to 6GHz. I would like to have the directional antenna array as it makes the most sense in my head. But if that's not possible, I can't decide between Pseudo-Doppler and Correlative Interferometry, it depends on technical requirements, information accessibility and price. Is there a commonly used method that I have missed?
Thanks for your time and help!
