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Comment by yonatan8070 | Hacker News Reader

This same devloper also built an SDR out of an ESP32 Wi-Fi microcontroller [1], this is awesome!

This development makes me hope that we'd be seeing more of these on common Wi-Fi cards, so that every random laptop could be used as an SDR for many fun and useful applications on a budget.

https://github.com/h0m3us3r/eSpDR

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Every wifi radio is an SDR under the hood. I'm not sure about this hack, but the ESP32 one was limited to just acting as an ADC + gain control. That leaves the guts of the radio still locked down, which limits a lot of use cases where you want wifi frames and time domain data. You either need to accept the latency and extract frames on PC, or add an FPGA, or use two cards fed from same antenna. Tx is also not possible.

The MT7996 chip is available with the banana pi R4 board, which has SFP+ (10 gigabit) so you'd have a near completely open ISM band SDR platform right there, feeding data to your server via fiber optics.

https://espargos.net/espsdr/

According to this TX is also possible on the ESP32-series chips, though they haven't published exactly how (I assume due they don't want to wake the FCC). But yeah the ESP32 is fairly limited in a lot of ways due to the limited processing power and IO bandwidth to stream data out of it

This should have full TX: https://github.com/cyber-murmel/esp-sdr-zephyr

Wow, these are coming out faster than I can keep up with them

I know for sure that Qualcomm LTE/5G modems are also SDRs under the hood.

Like Wi-Fi chips, they don't use SDR mode during most of the normal operation. They have dedicated hardware units that do a lot of the decimation, conversion, modulation and demodulation efficiently. But the "SDR mode" is still there for things like factory calibration.

Makes me wonder how many other common MCUs and SoCs are just waiting for someone to unlock SDR in them.

TX is less "not possible" and more "this dev doesn't want to enable it" from what I gathered. Probably for "I don't want people using this to shit all over the spectrum" kinds of reasons. So you can get TX - it'll just require extra hacking.

Yeah, I've worked on such chips where there is essentially a DSP with extra Wi-Fi specific hardware blocks on a shared memory bus. The DSP runs its standard assembly language and makes calls to the blocks, which are themselves configured with config registers or even a kind of microcode style assembly.

Those hardware blocks could be useful for certain applications but most importantly for triggering captures only when there are frames to process and giving you both the frame + the sample.

So for me the perfect hack would allow both normal Wi-Fi tx/rx and triggered or continuous rx sampling.

Yes they are. And they have a much wider tuning range (I have one that tunes from 240 MHz to 7 GHz). Problem of standard hardware is that every path has dedicated SAW/BAW bandpass filters that yeet anything not in uplink/downlink. And you need an unfused chip for custom Hexagon DSP stuff (so no phones).

Base stations are also SDRs by the way xD

Their DSP/SoC silicon includes a wideband transceiver? But phone chips have external bandpass filters? Interesting. Mostly I've seen baseband processor + external transceiver (wideband or not) with its own filters.

External transceiver over QLink.

I know the LTE modems had ADCs and DACs in SoC - ZIF with analog signal running straight between the tuner and the SoC. But 5G systems rolled ADC/DAC into the transceiver chip itself - with only the digital processing living in SoC.

Is the "QLink" setup they use in 5G systems now just a thin protocol running over LVDS and streaming I/Q between the transceiver and SoC DSP as digital signals?

Never actually went that far, but I did wonder if you could plug a QLink tuner chip into an FPGA to use it as a broadband SDR frontend.

There are also chips like NXP layerscape which do the sampling and hardware acceleration on a chip which streams to host (though still need another transceiver).

The motivation for this is of course beamforming, angle of arrival, spatial streaming, etc. You connect multiple antennas with different views back to the base station.

You can buy an rtl-sdr for ~$40 and have a much more interesting frequency range, plus you can use wifi to google stuff while doing it.

Receive only SDRs have been cheap for a long time now.

What are good, cheap, SDRs these days? Back when the first RTL-SDRs came out, I had an overview, but now there seems to be a gazillion variants, and every time I start researching I end up awfully close to buying a full HackRF that I'm drooling over but realistically don't have time to play with and which will just sit there gathering dust. Help! :P

Pick an RTL that does the ranges you are interested in and I doubt you can go wrong. The rtlblog v4 is recommended but hard to get ahold of now. They receive only but actually work quite well when paired with correct antenna.

HackRF is not as good at listening -- a bit deaf -- but does provide much larger bandwidth and obviously the low powered half duplex tx ability.

If you just want to grab random signals around and explore, get a cheap RTL.

If you really want to go back and fourth with a device, to modify data packets etc get a hackRF.

If you want to push beyond those limitations, you'll probably already know what you're shopping for next at that point.

Beware, you'll end up acquiring many different radio devices and then likely start building antennas out of scrap, buying a nanovna, and falling deeper and deeper into the magical rabbit hole!

> Pick an RTL that does the ranges you are interested in and I doubt you can go wrong.

Last time I was down this rabbit hole (when cheap RTL-SDRs were completely new), my favorite fun test was ADS-B, so let's say I wanna play around 1-1.1 GHz at first.

One day I also wanna sit down and do GPS from scratch, "by hand", so let's say I also wanna do 1.57 GHz (which I understand is becoming borderline difficult for the cheapest devices?).

Even though these devices are cheap, I'd rather avoid needlessly extra-shitty devices or my money going to copycat leeches.

Any recommendations in light of these requirements? Thanks a lot!

> HackRF is not as good at listening -- a bit deaf -- but does provide much larger bandwidth and obviously the low powered half duplex tx ability.

Yeah I know it's in a completely separate category, I just derail and start daydreaming ;-)

> Beware, you'll end up acquiring many different radio devices and then likely start building antennas out of scrap, buying a nanovna, and falling deeper and deeper into the magical rabbit hole!

Lol! I can see that danger very clearly!

Using an SDR is not "from scratch"

This is "from scratch": https://lea.hamradio.si/~s53mv/navsats/theory.html

You are of course absolutely correct! Let me rephrase: "from scratch" once the signal has been captured and I've avoided all the ways that hardware will fuck me over due to my lack of skills :-)

Very, very cool link!

If go down that route: get yourself a Rubidium standard, they're $150 on ebay and it will give you a rock solid clock to start off from.

RTL-SDR can do GPS L1CA signal processing easily, but you need to use the RTL-SDR Blog dongles not the blue no-name DVB-T dongles as:

- You need stable clock for the processing algorithms to be happy, RTL-SDR blog dongle have 0.5ppm TCXO while who knows what crystal they use on the no-name ones

- RTL-SDR blog dongles have bias-T, and a lot of GPS patch antennas are active antenna that need power from the coax to power the LNA

Good and cheap is probably still RTL-SDR and HackRF. Both solid at what they do. If you want a similar thing from a different maker you can check out the sbitx-v3 [1] (official platform of HERMES[2]). For more money there are a bunch of options and I don't have any personal experiece with the platforms, but I see people recommend bladerf or kracken. Reddit's /r/sdr is a great place for info.

[1] https://www.hfsignals.com/index.php/sbitx-v3/

[2] Recent discussion: https://news.ycombinator.com/item?id=49789228

HackRF is the gold standard, but definitely not cheap. I have an SDR-Play duo that I'm pretty happy with, writing software for it is doable (even though the manufacturer is really coy about what's in there you can dig into the driver easily enough). It remains to be seen how long those will be for sale though, I'm not sure if they're still making the chips (long story short: the SDR-Play seller once upon a time made a chip for another market and they seem to have realized they could make more money selling those same chips packaged to the SDR market).

"Damn, I forgot the garage code"

"oh, no problem"

>tippy tappy

>brrrrrrr

Is this your garage?

Does it matter? The door is open now.

Rest of the neighborhood too...

> so that every random laptop could be used as an SDR for many fun and useful applications

I guess the problem with these is they are more likely to be tied/tuned for specific (wifi) frequency ranges. Although 2.4GHz gives bluetooth and zigbee in addition to wifi

https://en.wikipedia.org/wiki/2.4_GHz_radio_use

It’d be neat to see this on ESP32-C5, which also has a 5GHz radio. S3 is 2.4 only.

https://espargos.net/espsdr/

ESP-SDR is based on this work, and supports the C5 and a bunch more

I think the lack of SIMD extensions on the C5/C6 holds it back, along with the bandwidth to get IQs out fast enough like you can on the S3/S31.

You'd still have to figure out how to replace the antenna.

The antennas usually included on ESP32 boards are for 2.4GHz, which is the range the ESP32 hardware is tuned for anyway. But if you do want a different antenna, just get a board with a modular antenna, like some of the Xiao boards from Seeed Studio

Yes, that was in the 'random laptop' context, sorry, I could have made that clearer.

I think that applies too, laptops usually use the same connectors for the Wi-Fi antennas, so you shouldn't have an issue just using something off the shelf that matches the frequency you want

I was really excited about this, but as an average home assistant user couldn't really see an application, lol.

For an SDR? Me and my buddy Claude put the ceiling fans and a bunch of our light plugs onto a homebrew remote I built from a chip and an SDR. Would have gotten the tire pressures from the cars too, but they’re available via Bluetooth.

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