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Comment by gspr | Hacker News Reader

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

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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).

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