Practical SDR: Getting started with software-defined radio
74 comments
·May 30, 2025_whiteCaps_
ews
Literally me right now, got my first SDR less than a month ago because I wanted to have an FM radio for emergencies and I am designing antennas and studying for my amateur radio license.
driggs
If you want an FM radio for emergencies, get a battery-powered analogue FM radio, not a computer running SDR!
diggan
> because I wanted to have an FM radio for emergencies
Just make sure you have batteries/a way to run it!
When we lost electricity for 1.5 day here last month (Spain), I thought I'd be clever and use my SDR too, but since we didn't have electricity at all, and none of my laptops were charged, I was out of luck. Wife's Macbook had battery available, but since I never used it with her Macbook, of course it didn't have the software/drivers needed, and the internet didn't work as all ISP equipment was also without electricity. Ended up listening to the radio in the car which was more than cumbersome :/
TLDR: get a shitty battery/hand-crank powered FM/AM radio for emergencies
varispeed
Remember schematics for radios powered just by radio waves. No need for battery or hand-crank. That was in some old books, but never managed to build one.
_whiteCaps_
Good luck with the license! There's lots of people on Mastodon that chat about radio stuff.
ews
Thanks ! What accounts should I follow ?
mycall
Packet radio, srsRAN, LoRA, Doppler Radar. So many fun things to do with SDR.
polishdude20
If anyone wants ideas, try and get on the WISPR network! All you need is like 20 ft of wire and an SDR and you can listen to signals from across the ocean easy.
cess11
WSPR, WISPR is something else.
https://www.rtl-sdr.com/a-tutorial-on-receiving-wspr-with-an...
viraptor
Confirming this. Sounds like a joke but suddenly Ali knows just how how to snipe you with radio equipment offers...
UtahDave
$3k is barely getting started. Literally barely getting started.
But you love it anyway
geeunits
One of the few hobbies in my adhd/ult life that has sucked me in and spat me out precisely as described
agiacalone
And then there's the license upgrades!
zoklet-enjoyer
I will avoid it for now because I don't think my wallet can handle it. I got really into home brewing for a while. Then synthesizers and drum machines. I need to stick to cheaper hobbies
tecleandor
Admiral Ackbar says... "It's a trap!"
0xEF
If anyone sees this No Starch book (which is decent, btw, as one can expect from No Starch) and wants to dive in, start here: https://www.rtl-sdr.com/rtl-sdr-quick-start-guide/
There's a lot of garbage equipment out there and it's easy to buy something that does not work or creates spurious emissions or other weird interference and incompatibilities. Unless you know how to mitigate these issues with a deeper understanding of electronics and RF, you're going to struggle to get good results.
That site is easily the most comprehensive starting point for beginners, but read through it carefully before purchasing a dongle.
drweevil
I second the rtl-sdr.com site.
There's a lot of cheap (as in not very good) stuff out there. I have 3 goto SDRs in my collection. The RTL-SDR.com Blog V4 dongle is a great--and affordable--starting point. You're only out ~$40 if you decide this isn't for you, but if it is, the 27 MHz to 1.6 GHz coverage will keep you busy. If you are a ham, or enjoy short wave listening, go with the Airspy HF+. Covers 0.5 KHz (I've seen reports of ultrasound experiments with this!) through HF, and VHF bands. For the price, this is the highest quality SDR I have. Great sensitivity, low noise. Rounding out my small collection is the Great Scott Gadgets HackRF One, which is pretty much a radio lab in a box. 1 MHz to 6 GHz, 20 MS/s (albeit at only 8-bit quadrature sampling), and can transmit. (As an added bonus their teaching videos are very good.)
BTW, I have no problems with running these 3 SDR devices on Linux, if that is a consideration.
net01
I love SDRs, I use mine to record the microphone signal of my professors. much better than using a phone or a dedicated recorder!
HWR_14
I take it they are using a lavalier microphone during lectures that broadcasts the recording in an unencrypted format? If so, that's a great solution.
net01
Yeah, they are using Sennheiser transmitters (some are lavs some are full XLR mics ) Basically, I am using an SDR(RTL-SDR V4 with a small antenna) and SDR++ they have set frequencies that I have bookmarked and saved.
Funny thing, this allows me to listen to courses in other rooms, its quite fun to tune in and guess the class xD
darthcloud
A good free resource to learn is https://pysdr.org/
This is not a python module, but a guide to learn the basic of digital signal processing using python in the context of using a SDR. It also goes into the specific of using the most popular SDR HW.
ash-ali
Table of contents & the books description seem a little gloomy to anyone else?
GNU Radio, filters, AM/FM, IQ demod ... I remember working through all these topics on GNU Radio Tutorials wiki [0] but I don't know if the book offers anything more of value?
Also, if the authors focus on GNU Radio as their software stack why would they not include a chapter on creating your own Python Blocks which is the biggest upside (imo) to GNU Radio. I love SDRs and think anyone interested in electrical engineering should play around with them. I dont know if I'd recommend this book based off what the sample chapter 4 provided.
jcims
I think sending people directly to GNU Radio is a bit of a risk. Sending folks that just learned how to spell SDR deep into the bowels of DSP is a bit steep of a learning curve that many might equate with a brick wall.
A little over ten years ago (!) I got started with a windows box, sdrsharp and a cheap RTL-based SDR. Just cruising around the spectrum, clicking on signals that were interesting, cobbling together decoding pipelines and getting real results was a way better way for me. Getting started with software that works and interesting use cases you can get into with cheap hardware got me hooked and THEN I had something that I was genuinely craving an understanding of to drive me into GNU Radio.
perrygeo
Agreed, GNU Radio exists in this weird no-mans land where it works on low-level concepts wired up with high-level guis. Do not want. I want to playing with CubicSDR to zoom around the spectrum, then if I I need to do anything fancy with the data, switch over to signal processing and start writing code.
focusedone
Handy map of online web SDRs if you'd like to play with one while waiting for yours to ship :-)
abhisek
Tried playing with SDR a while back. Back then, biggest challenge was to find an appropriate hardware that can receive at various frequencies and also compatible with my Linux box.
Pawka
Hermes Lite is not _so_ expensive and decent open source project: http://hermeslite.com/
noman-land
The HackRF has a super wide range and works great. Highly recommended.
viraptor
Rtlsdr are extremely cheap to start with. Then maybe Hackrf one? They're all (?) trivial to use on Linux these days.
joker99
If you want to go even a step up in the trvial to use ladder, there's the Portapack H4m project. It builds on the HackRF One and adds a screen, custom firmware (open source, extensible) into an handheld factor and lets you do a bunch of... _stuff_ without needing a computer :) Also not _that_ expensive, I got mine for about 400€ from lab401.
azernik
Things have improved a lot. These days GNU Radio (via OsmoSDR) supports all the big hobbyist-price-point SDR vendors, and most of them go from ~50MHz to ~6GHz.
Havoc
Is there any sort of automatical signal detection tech out there. i.e. something that identifies part of spectrum that aren't noise automatically?
The cheap SDRs have pretty narrow receive windows so would be helpful
zhengyi13
The way I read your question, anything that will display a waterfall is what you want; you'll see crystal clear that there are signals wherever they might be, and you can just click/tune over to that frequency. You typically can zoom in or out on that waterfall to cover broader or narrower ranges.
You can get this with either full on (expensive!) radios, or with a cheap RTLSDR dongle paired w/ appropriate software on your computer. And to what you said about cheap SDRs... 24 to 1766 MHz isn't a particularly narrow range from my point of view, but if you're willing to spend some more money, the HackRF One will cover 1MHz (160m band) all the way on up to 6GHz (wifi). Going lower or higher than that probably needs more specialized stuff.
(And of course, appropriately tuned antennae hooked to the radios/dongles)
Havoc
I do have a hack rf one just not unboxed (for a while it sounded like UK might ban SDR sales so preemptive buy).
I was under the impression that the spectrum is quite large relative to what you can look at with a waterfall and thus would take forever. Based on your comment sounds like I might need to take another look!
ThrowawayR2
Specialized hardware exists for that. Google for "spectrum monitoring".
sorenjan
If you want another use for SDR, the KrakenRF kan be used to find radio transmitters.
nickledave
No one asked, but, if you're here: check out this (new-ish) Python library for SDR that is really well designed and developed (IMHO) https://mhostetter.github.io/sdr/latest/
rsync
There used to be an all-in-one boot image for the raspberry pi:
https://github.com/luigifcruz/pisdr-image
Unfortunately it appears to have been abandoned ...
drmpeg
There's the similar DragonOS for the Raspberry Pi.
Be careful with SDR's. One minute you're scrolling around the spectrum, and the next you'll find yourself ordering parts for a 36 element Yagi and AZ/EL rotator, and a $3k radio to do Earth Moon Earth bounce communication.