[HN Gopher] CaribouLite: Turn any 40-pin Raspberry-Pi into a Tx/...
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CaribouLite: Turn any 40-pin Raspberry-Pi into a Tx/Rx 6GHz SDR
Author : todsacerdoti
Score : 167 points
Date : 2021-06-17 14:19 UTC (8 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| SavantIdiot wrote:
| I'm eager to see if it is more stable than SoapySDR, OsmoSDP,
| CubicSDR. I find that all three tend to be fickle cross OS.
|
| I use a HackRF One, and I _can_ scan up to 5GHz, but it is
| painful: the bandwidth depends a lot on the hardware. You need
| ~$20k in radio hardware to effectively scan a usable part of that
| domain, and by that point it is better to just invest in a RTSA.
| parsecs wrote:
| Or use better engineered hardware. HackRF One had some very
| weird hardware designs that don't perform well for the price.
| thatcherc wrote:
| Super cool! I like the block diagram [0] they have on their
| crowdsupply page [1]. It's a really clear illustration of how the
| board is set up with just a handful of high-level components. SDR
| schematics are usually pretty hard to parse without background in
| RF (which I certainly don't have) so I appreciated the system-
| level breakdown. Definitely a project to follow!
|
| [0] - https://www.crowdsupply.com/img/64f0/cariboulite-block-
| diagr...
|
| [1] - https://www.crowdsupply.com/cariboulabs/cariboulite
| avian wrote:
| This project certainly seems to have the documentation on a
| higher level than what I'm used to. It's rare to see such a
| readable schematic with extensive comments on specific parts
| (FPGA programming, RF path, ...).
| jpm_sd wrote:
| This is a cool hack, but seems to have been built on a pretty
| fragile foundation. Why not use one of the existing dedicated SDR
| boards on the market?
| GekkePrutser wrote:
| Price probably, those are all in the several hundred dollars
| range especially with 6ghz and tx.
| h2odragon wrote:
| Very cool! makes me wonder what the Pi can _do_ with all that
| data being stuffed into it; I had no idea there was any chance of
| that much I /O to them.
| sounds wrote:
| I am guessing that the Lattice ICE40LP FPGA would help a lot
| with data processing.
| avian wrote:
| I doubt that FGPA will do anything else than interfacing
| between the AT86RF215 and the Raspberry Pi. It is pretty
| small in terms of the number of gates - but also cheap
| (around $3 at quantity).
| zokier wrote:
| Is there lot of use for <4Mhz bandwidth channel at 6GHz? Seems
| pretty narrow/imbalanced spec to me, but then I don't know that
| much about SDR.
| rektide wrote:
| Had no idea about this:
|
| > CaribouLite utilizes the SMI (Secondary Memory Interface)
| present on all the 40-pin RPI versions. This interface is not
| thoroughly documented by both Raspberry-Pi documentation and
| Broadcomm's reference manuals. . . . The SMI interface allows
| exchanging up to ~500Mbit/s between the RPI and the HAT, and yet,
| the results vary between the different versions of RPI.
|
| Way cool that the rpi has a high bandwidth interface! From the
| write-up, sounds like it's been quite the adventure from numerous
| parties to explore & make use of this capability. But oh how
| fruitful! Half a Gbit in some cases, sweet!
| pedrocr wrote:
| The compute module version of the RPI exposes PCI Express. If
| I'm reading the specs correctly it should be able to do 500
| MB/s so 8x this interface.
| outsomnia wrote:
| This interface is simple enough that a cheapo fpga like
| Lattice can speak it without needing to support PCIe.
|
| I have to say the noise floor on that spectrum analyzer sat
| on top of a cpu + ddr like that is going to be pretty nasty.
| djmips wrote:
| The noise issue is something that hadn't occurred to me; It
| would be interesting to hear some first hand experience
| from the developer.
| GekkePrutser wrote:
| Indeed and it doesn't even have any shielding cans on it in
| the design they show on crowdsupply.
| RachelF wrote:
| The key missing RF specification is sensitivity.
|
| Without knowing this number it is probably better to classify
| this board as an oscilloscope + signal generator.
| Erwin wrote:
| What's special about these frequencies to exclude them?
| 2398.5-2400 MHz and 2483.5-2485 MHz
|
| Unless that was meant to be 2483.5-2495 which is something called
| "Globalstar".
| kam wrote:
| They're using a transceiver that only operates in the 2.4GHz
| ISM band, and putting a mixer in front of it to
| upconvert/downconvert frequencies beyond that. These ranges are
| probably the gaps between what the AT86RF215 can handle on its
| own and the frequencies at which the mixer kicks in.
| Avamander wrote:
| How does it compare to RTL-SDR specs-wise?
| sschueller wrote:
| Also how hot does it get? Those dongles get crazy hot.
| djmips wrote:
| RTL-SDR can't transmit (only RX)
|
| RTL-SDR can only go up to around 1.7 GHz which is a big issue
| if you want to analyze most modern RC stuff for example.
| sokoloff wrote:
| The biggest difference is the rtl-str (DVB-T) dongles are
| receive-only while this is a transmit-capable SDR.
| calebm wrote:
| Sounds awesome! Anyone tried this?
| ilaksh wrote:
| Is it possible to talk to cell towers with this?
| ac29 wrote:
| There are plenty of relatively inexpensive chips that support
| LTE and are legal if you're actually interested in this.
| stagger87 wrote:
| Possible? Maybe at the cellular 3.84MS rate. Legal, no.
| extrapickles wrote:
| It in theory could do GSM, though you might need two, depending
| on if it can tune from the tower->handset and handset->tower
| frequencies fast enough.
| [deleted]
| Aachen wrote:
| "Turn any raspberry pi into an SDR"
|
| ... by adding hardware to it. The headline made me at least think
| it somehow uses the pins as antennae, also because people have
| done this sort of thing in the past.
| tinus_hn wrote:
| The interface having enough bandwidth to do this is interesting
| Aachen wrote:
| Ah, I did not know that. I've always worked with USB SDRs, is
| a regular USB3 higher bandwidth than these pins?
| blihp wrote:
| USB 3 can provide orders of magnitude (how much depends on
| which rev) more bandwidth. This device provides slightly
| more bandwidth than an RTL-SDR stick over USB 2.
| jcrawfordor wrote:
| USB2 can do 10MSPS easy, but in my experience small SBCs
| like the Raspberry Pi struggle to keep up with this rate at
| the CPU. Might be more practical with the newer models, but
| I gave up on an RPi 3 with a 10MSPS SDR because it was
| excessively dropping samples at around the 5MSPS point...
| so it's possible that 4MSPS is approaching the limit of the
| CPU, at least for a given level of optimization of the
| software tools (I was mostly just sending out I/Q samples
| over the network).
| dragontamer wrote:
| It seems to only support 4 Mega-samples/second, which isn't
| much bandwidth.
|
| EDIT: Its a fair bit of bandwidth for an embedded system like
| Rasp. Pi, so I'm not trying to undersell the project. But
| we're looking at 32-bit samples at 4MSPS, or ~16MB/s
| bandwidths here.
| GekkePrutser wrote:
| 32-bit samples is a lot for an SDR though!
| gswdh wrote:
| It's one or two 13 bits samples from the ADC padded out
| to 32 bits. True 32 bit ADCs do not exist.
| robocat wrote:
| From article "each ADC sample contains 13 bit (I) and 13
| bit (Q), that are streamed with a maximal sample rate of
| 4 MSPS from the AT86RF215 IC. This channel requires 4
| bytes (samples padded to 32-bit) per sample (and I/Q
| pair) => 16 MBytes/sec which are 128 MBits/sec. In
| addition to the 13 bit for each of I/Q, the Tx/Rx streams
| of data contain flow control and configuration bits."
| stefan_ wrote:
| They are doing 500Mbit/s over these pin headers, don't worry
| they are a freaking antenna all right.
| djmips wrote:
| It's pretty tightly integrated so I give it a pass. I like the
| design a lot.
| gregsadetsky wrote:
| Same. Here's a Pi-based FM transmitter that uses no additional
| hardware except for an antenna:
|
| http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...
| londons_explore wrote:
| I wrote that code. It's mostly broken nowadays because newer
| pi's use different hardware and new Linux distributions lock
| down the ability to poke random memory without the kernel
| having a proper driver.
|
| There are other pifm projects which use the same general idea
| and work properly though.
| gregsadetsky wrote:
| Amazing, thanks! Would you have a links to those other
| projects or their names? Would love to read more.
| dTal wrote:
| Note: do not use this. The carrier wave is a _square wave_
| which means you spill ungodly amounts of RF into harmonic
| sidebands. If you dare to plug this into an amplifier - at
| least without a lowpass filter - expect a firm knock on your
| door.
| klysm wrote:
| Isn't the point that you use this without an amp though
| dTal wrote:
| It's still illegal (and possibly dangerous) even without
| the amp - you're just much less likely to actually
| interfere with anything because the range is short. But
| you still shouldn't use it.
| omginternets wrote:
| Could you elaborate? As someone who has been interested
| in hacking SDRs for a while (but with zero prior
| knowledge outside of programming), I'm often worried that
| I have a poor barometer for what is legally dangerous.
| This stuff seems innocuous enough, but isn't always.
|
| I don't know what I don't know, so any additional context
| is welcome.
| haswell wrote:
| Generally speaking:
|
| - Listening is typically OK (with some exceptions).
|
| - Transmitting is a minefield, and you could interfere
| with critical systems, cause outages, and get in trouble.
| Imagine interfering with aircraft communication systems
| on accident because there's an airport nearby. Things can
| get pretty serious pretty quickly.
| parsecs wrote:
| What are exceptions to listening? I'm pretty sure you can
| listen wherever and however you want.
| [deleted]
| wdfx wrote:
| You're not strictly allowed to decode and read pager
| messages.
| klysm wrote:
| Out of curiosity, what laws does it violate?
| SV_BubbleTime wrote:
| All manner of jamming and FCC broadcast rules.
| klysm wrote:
| Yeah but specifically, I just don't know anything about
| these laws and it seems fine to be doing it at low power
| gsich wrote:
| Low power means nobody is going to notice.
| netr0ute wrote:
| Problem is, the kinds of people who are interested in
| this kind of thing don't care if it's illegal or not.
| haswell wrote:
| They'll start to care pretty quickly when they get a
| visit from a 3-letter agency (just one example [0]).
|
| - [0] https://www.jdsupra.com/legalnews/fcc-enforcement-
| bureau-tar...
| CamperBob2 wrote:
| Realistically, that's not going to happen unless a
| harmonic lands within the ATC band or a GPS subband.
|
| The trouble is, _that 's_ entirely possible. This sort of
| thing needs a good enclosure, or at least some board-
| level shielding.
| lstepnio wrote:
| 99.999999999% not going to happen. On the remote chance
| does, expect a simple educational talk.
| mlyle wrote:
| You're pretty damn likely to be inside the part 15 mask
| which is hundreds of microvolts/meter (30m away) up at
| UHF+. The total energy inside a single GPIO squarewave is
| on the order of 30mW; harmonics are a tiny fraction of
| this, and most will not be radiated efficiently. (Not to
| mention that edge rates/stray capacitance will limit
| their energy in the first place).
|
| The big question is whether the fundamental frequency is
| compliant. A perfect squarewave has ~81% of its energy in
| the fundamental frequency.
| jandrese wrote:
| Anybody have a guess at the price point for this board once it
| launches? Competition is stuff like the HackRF One at $120,
| although this is less capable.
| pmorici wrote:
| The three main parts (Modem + Mixer + FPGA) cost on the order
| of ~$18 in medium volumes throw in other required components,
| PCB, and assembly and I'd guess their cost all in is just under
| $30 when made in quantities of 1,000+. Add in profit margin and
| I'd guess they will offer it in the $40-$60 range.
| jandrese wrote:
| That's pretty reasonable. Call it $100 once you add in the Pi
| and SD card for a useful SDR platform. Have to add whatever
| antenna you are using too I guess.
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(page generated 2021-06-17 23:00 UTC)