Practical SDR: Getting started with software-defined radio | Hacker News Reader

Practical SDR: Getting started with software-defined radio

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260 pointsteleforce78 comments

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.

Confirming this. Sounds like a joke but suddenly Ali knows just how how to snipe you with radio equipment offers...

I was already building a homelab, and was eyeing SDR and Meshtastic gear.

Don't do it!! Next you'll be setting up a weather station. Then you'll be setting up a microphone to ID birds via Merlin. Then home Assistant. Oh gosh it never ends.

But it's so much fun.

This comment is targeting me personally.

Well now I'm looking at automatic bird id and logging so I can track local species and see what my attempts to turn my stretch of grass into a wildlife garden does... Thanks, I think?

I'm so sorry. Lol

They are all ready on my to do list, but just those three things.

So far. While at it consider storing all the Linux isos ever existed too

I feel attacked.

What weather station did you end up with? And if it’s already been set up, is it proving to be more useful than local weather stations?

$3k is barely getting started. Literally barely getting started.

But you love it anyway

My buddy is one of the top station builders and contesters. He says it is a about $10,000 per tower. And one tower won't do.

The hell are those guys doing? I always had the itch, but never pulled the trigger on getting my feet wet into SDR. Radio astronomy?

It's a ham radio contest station. Doesn't really have to do with SDR.

https://www.youtube.com/watch?v=Dd4NWyFq-dM

Tim’s station is one of the biggest in the world. His tallest tower is 240 feet high.

Some stations do use SDRs to feed the reverse beacon site. https://beta.reversebeacon.net/main.php

And then there's the license upgrades!

Only 3K to bounce shit off the moon?

No... 3k just for the radio - actually, an IC-9700 is about $2k now.

Then add the yagi antenna, az/el moon tracker, amplifier, coax, etc. It really starts to add up.

I've never done this but I've worked a bunch of satellites and the ISS repeater. It's generally the same stuff, just a bit more powerful and precise.

Can be done more cheaply if tou are good at reusing things and building.

Can be cheaper than that. I picked up 2 used icoms for about $500. I haven't tried to moon bounce with it yet, but the one should be able to (and do satellites too). So the radio by itself would have been about $300 and the antennas are self built.

One of the few hobbies in my adhd/ult life that has sucked me in and spat me out precisely as described

What’s ult?

adult with adhd I assume?

That makes sense, thanks. Ad[hd/ult].

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.

Good luck with the license! There's lots of people on Mastodon that chat about radio stuff.

Thanks ! What accounts should I follow ?

Anyone on mastodon.radio, and check out the #amateurRadio topic.

> 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

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.

I could be wrong but I think that only works for AM, not for FM.

supposedly you can demodulate FM with "slope detection", off tuning slightly so as the signal varies in and out of the resonance of the tuned circuit you can get an audio signal. Its gonna be mono lol. The "Q" of the tuned circuit needs to be pretty good and its interesting to see that they use copper tubing as the coil wire or more technically in the linked page, a resonator.

https://electronbunker.ca/eb/FMCrystalSet.html

That's AM crystal radio but there aren't that many AM stations left these days, most have been torn down because (thanks to AM) they need insane amounts of power to be receivable across larger distances.

Not in the USA. We still have 50,000 watt clear channel stations. On a clear winter night, local lore has it that WJR-760AM Detroit could be heard in Mexico. Crystal radios still work...well, not fine, but as good as they ever did. AM frequencies are low enough they skip off the ionosphere.

I remember a family road trip from Chicago to South Carolina in our '77 Impala wagon, when my whole family was listening to a DePaul basketball game on WBBM Chicago. My dad was a big fan. It was late at night, and the game came down to the last shot in the last second or so. The station was barely coming in, so we pulled over and heard DePaul win on a buzzer-beater... then the station blinked out. It was perfect.

I always think about this when I see another story about AM's demise.

> We still have 50,000 watt clear channel stations

On shortwave, we even have 250,000 W transmitters just blasting RF everywhere.

We call them flame throwers for a reason.

Mmm, I think you may have AM and FM reversed there. If I remember correctly, FM only goes 65 miles or so, but AM can go thousands of miles under the right conditions (at night, mostly).

If you want an FM radio for emergencies, get a battery-powered analogue FM radio, not a computer running SDR!

Packet radio, srsRAN, LoRA, Doppler Radar. So many fun things to do with SDR.

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.

WSPR, WISPR is something else.

https://www.rtl-sdr.com/a-tutorial-on-receiving-wspr-with-an...

Admiral Ackbar says... "It's a trap!"

... and time and money for acquiring a ham license!

Followed by more thousands of dollars for HF and 2m/70cm rigs, followed by more thousands of dollars for Hamnet links, a QO-100 sat dish for the Europeans...

You can do it on the cheap with CCRs and estate sales. My Kenwood HF unit was bought for $250, I made wire dipole antennas. I'm surrounded by Baofeng equipment as I type this. Total outlay for all of it probably on the order of $1000.

I do so want an Icom 7300, though.

I'm so jealous of the people that can see QO-100. Here I am in Canada checking my app for the birds to fly over, and people on the other side of the world can just point their antenna at it any time. :-/

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

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.

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.

Have you don’t any transmitting with the HackRF One? What was the experience like?

I love SDRs, I use mine to record the microphone signal of my professors. much better than using a phone or a dedicated recorder!

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.

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

I absolutely love these little capabilities that (cheap) SDR opens up to pretty much everybody.

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.

[0] https://wiki.gnuradio.org/index.php/Tutorials

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.

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.

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.

Handy map of online web SDRs if you'd like to play with one while waiting for yours to ship :-)

https://www.receiverbook.de/map

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.

Rtlsdr are extremely cheap to start with. Then maybe Hackrf one? They're all (?) trivial to use on Linux these days.

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.

Hermes Lite is not _so_ expensive and decent open source project: http://hermeslite.com/

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.

The HackRF has a super wide range and works great. Highly recommended.

https://greatscottgadgets.com/hackrf/

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

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)

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!

You might also want to take a look at "RF Explorer Spectrum Analyzer"; nice handheld devices with varying frequency ranges - https://j3.rf-explorer.com/

Specialized hardware exists for that. Google for "spectrum monitoring".

If you want another use for SDR, the KrakenRF kan be used to find radio transmitters.

https://www.krakenrf.com/

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/

Thats how Russ Hanneman made his money.

ROI?

Also relevant: Michael Ossmann's tutorial Software Defined Radio with HackRF - https://greatscottgadgets.com/sdr/

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 ...

There's the similar DragonOS for the Raspberry Pi.

https://sourceforge.net/projects/dragonos-pi64/

This is a gentle reminder that this text book might be applicable, depending on how you use your SDR:

Communication Systems Engineering with GNU Radio: A Hands-on Approach Jean-Michel Friedt, Herve Boeglen

https://www.wiley.com/en-fr/Communication+Systems+Engineerin...

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