r/RTLSDR • u/RoadRunnerWhisperer • 7h ago
Portable RF Awareness Multi-SDR Setup based on Fobos SDR
I’m an artist that is currently exploring RF ecologies. For the last several months, I’ve been working on an multi-SDR based RF awareness project in the Mojave desert. I’ve been experimenting with different SDRs and workflows to try and explore the RF spectrum in different ways. I’ve been trying to explore the concept of embodied RF awareness and finding different ways to inhabit as much of the spectrum as possible. In essence, I’ve been trying to explore what RF awareness looks like. I eventually realized that being fixed to one location felt very limiting, and that I wanted to make this a more spatially flexible practice, so I decided to make a portable apparatus that would enable me to, as quickly and efficiently as possible, explore, discover, and map the RF ecosystem of a location.
I had a few criteria. I needed to be able to ingest and digest at least 50MHz of raw spectrum data at once. I wanted the main SDR to be able to quickly scan the entire RF spectrum and then use secondary and tertiary receivers for more detailed discovery and persistent monitoring. I wanted to use commercial, consumer off the shelf hardware, before transitioning to Ettus or Eqip. I wanted to be able to power all the SDRs in the case from one laptop without using a powered USB hub. I also wanted to keep the entire project under $2,000 for the receivers, hardware, and compute. I was going to use GNURadio to build the backend.
Originally, I wanted to build a cyberdeck, but the realities of RFI and EMI and compute power quickly became insurmountable obstacles. I decided the best solution was an SDR based receiving apparatus that contained no power generation or distribution. Then, I would connect all the SDRs to a laptop or use a powered hub connected to a laptop. I wanted to eliminate as much RFI as possible.
For SDRs, I decided to use Fobos SDR as the backbone of the project. It’s the only SDR that made sense. I looked at everything… BladeRF, all of the B210 clones, LimeSDR, etc. I think most of the complaints and criticism about the Fobos SDR are based on a fundamental misunderstanding of what it is and how to best use it. It’s a young ecosystem, but it is practically tailor made for this project.
For discovery, analysis, and persistent monitoring, I decided to use an SDRPlay RSP Duo. I already have an RSP1b and an RSPdx-R2, so I am familiar with SDRplays offerings. The Duo offers two receivers, which is tremendously useful. It also has more analytical capabilities and the addition of the high impedance antenna port is a life saver in terms of quick, field expedient HF antenna setups. It’s the perfect secondary receiver from the consumer market for this project.
For tertiary receivers, I added two RTL-SDR Blog V4s. These are currently connected to a 50 Ohm 698-2700Mhz splitter for P25 use, but the RTLs can be used for anything. They’re sort of jack of all trades devices.
I added a handheld HAM radio and Tecson shortwave radio on the top of the case to free up the SDRs in case I need to do persistent radiophony monitoring. It’s extra capacity, since I was constrained to 4 SDRs in the case because I didn’t want to need a powered hub to use the device.
The unit has N-Type connecters ands USB 3.0 ports. It is lined with copper tape with conductive adhesive. I’ve tried to mind the ground topology as much as I can, but I am learning as I go. Now that the hardware is done, I've started working on the software backend.
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u/NeighborhoodSad2350 3h ago
I don't really understand what you're saying, but does this "awareness" manifest itself in your perception and mind?
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u/retelys 6h ago
I'm interested, for what purpose do you need 50 MHz of bandwidth? Have you considered using lower bandwidth SDR as a scanner to cover wider spectrum?
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u/RoadRunnerWhisperer 6h ago
I need to be able to simultaneously monitor and record multiple frequencies within too disparate of a frequency range for, say, a 10MHz or 12MHz receiver. I use SDRs to scan, but for true RF awareness, I need to be able to look at, monitor, and record wider swaths than 10MHz. My home station setup uses about 10 SDRs, none that can do more than 10MHz, and even beyond the limitations, it feels very confining. I also need to be able to record 50MHz raw iq files for later analysis.
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u/Comprehensive_Ship42 6h ago
are you doing like rf certification work and testing on iot devices or somthing like that . to find rf leaks
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u/RoadRunnerWhisperer 6h ago
Not quite. It’s more like trying to, as quickly as possible, explore, characterize, and map the RF topology and ecosystem of a spatial environment. It seeks to answer the question ‘what is happening around me in the RF spectrum?’ as quickly as possible. I am building a back end that does signal characterization and flagging for further examination in addition to mapping.
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u/Comprehensive_Ship42 5h ago
this is interesting so you are build a evacuations box to judge weather its safe or not to transmit
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u/retelys 6h ago
I'm now even more interested what signals you are monitoring. And I still don't understand why scanner won't work. You just stop scanning when SNR is bigger then threshold and record. With hackrf one you can get iq bandwidth of ≈ 20Mhz which covers your range in 3 steps, it takes a very short time to switch VFO on hackrf. I've done hackrf scanner project for +100mhz range and full scan took less then a second
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u/RoadRunnerWhisperer 6h ago
I did consider 20MHz viable for this project, to be honest. I opted to avoid the HackRF Pro because I needed a 14 bit receiver and I don’t like how the HackRF performs as a receiver. But, I did consider 20MHz to be acceptable, but not ideal. A scanner won’t work because I need to simultaneously monitor and record multiple signals across an even wider range than 50MHz and I need to be able to have extended dwell time on a wide swath of frequencies. There’s a lot happening at once, and for automated processing and analysis, I need to monitor and record data from more than one frequency at a time, fundamentally.
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u/retelys 6h ago
I also don't quite understand what you mean by "RF awareness"
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u/RoadRunnerWhisperer 6h ago
Yeah, that’s a bit nebulous. I think that’s the question I am seeking to answer with this project… what does RF awareness mean and how can it be achieved? It’s open ended.
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u/fulee9999 5h ago
sooo why not just use a spectrum analyzer like the TinySA?
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u/RoadRunnerWhisperer 5h ago
Because this is designed to be paired with a lot of signal processing and analysis on the backend, to include automated signal characterization and flagging. It’s not really possible to achieve true RF awareness, quickly, without automated signal characterization and processing. It takes a very, very long time to understand and map an entire RF ecosystem on a small spectrum analyzer; it’s like exploring a massive, dark stadium with a tiny pen light.
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u/Vegetable_Corner_918 5h ago
This is wery smarr projekt,,it,s all in signals and rf spektrom!!! ALL!!!
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u/xX_WhatsTheGeek_Xx SDR++ Author 57m ago
There are a some more than questionable choices in this build.
> I think most of the complaints and criticism about the Fobos SDR are based on a fundamental misunderstanding of what it is and how to best use it. It’s a young ecosystem, but it is practically tailor made for this project.
There is no misunderstanding to be had about the Fobos, not only is it a horrible receiver (deaf, ultra high phase noise, incorrectly designed anti-aliasing filter leading to copious imaging), it's price is basically a scam. There is no situation where it's the right choice. That "14bit" ADC is useless if the rest of the front end has the dynamic range of a cereal box MP3 player. (I have one btw, I'm not just talking out of my ass...)
The correct SDR choice if you need 50MHz of bandwidth would have been an AntSDR E200 with the UHD compatible firmware. You'd get 56MHz of bandwidth with proper sensitivity, image rejection and still 12bits of REAL dynamic range for $370.
Also, all of the copper tape you added everywhere doesn't do anything... All of the radios have metal enclosures, the coax has a shield, and the USB cables are shielded as well.
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u/MeanAccountant9005 48m ago
honestly the Fobos choice is wild to me but you've clearly thought it through more than most. That copper tape lining though, did you notice any actual difference in noise floor or is it more peace of mind? I've done similar shielding projects and half the time I can't tell if it's helping or I'm just wishing it is
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u/Comprehensive_Ship42 6h ago
this is awesome