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LimeSDR Mini – An open, full-duplex, USB stick radio for femtocells and more (hackaday.com)
171 points by smokielad on Sept 23, 2017 | hide | past | web | favorite | 46 comments

I get to recommend one of my favorite sites again.


You can also just go to http://websdr.org and select from a bunch of other servers.

Basically, the site is an SDR with a web interface. You're able to go there and listen to the radio. It is, obviously, RX only. Still, you can go there and listen to the ham radio enthusiasts across the world.

I should warn you, it is quite a time sink. Not everything is in morse code. You can stumble across some interesting stuff and it is fun just playing with the buttons.

If you've wondered what ham is all about and haven't bothered to get your license, this is a great way to experience the monitoring aspect of being a radio operator. If you're anything like me, it will eat up more time than you'd care to admit.

Still, it is an SDR that you can actually play with to see if you're interested in learning more about it.

I just want to caution folks about visiting this site. You could find yourself getting sucked into a years-long obsession with RF and software defined radios. Pretty soon you'll have dozens of RTL SDRs strewn about your desk, coax tumbleweed snaring your feet and six iterations of a quarter-wave ground plane that still don't work quite as well as the first one you ever built.

That site is really awesome, I've spent a lot of time there as well (for those interested, check out the "Chatbox" tab, where users share stations/frequencies).

Do you think that it would be useful to have an in-browser audio decoding of signals, i.e. support for various digital mode, as fldigi [https://en.wikipedia.org/wiki/Fldigi] does?

Tune in to a station, and see the morse output right in the browser..?

Absolutely. I'd also like to see an attempt to translate the output to the user's native language.

What I'm not sure of is if the signal will always be good enough to decode it. In fact, I suspect it won't always be good enough to decode it automatically.

Obviously, we shouldn't let perfect be the enemy of good and it should just fail gracefully when the signal is degraded too much.

But, it potentially becomes a support nightmare. While we may know that the trouble is the signal degradation, I suspect many people wouldn't and they would try to place blame on the developers. It may make identification of actual software problems more difficult to assess.

Still, I say it would be a 'killer feature.' I have pondered it before but I'm not a very good programmer. I am pretty sure that some of them would happily add it right to their site, should someone make it. There are a lot of great features that could be added along with it - such as outputting it to a chat room that was dynamically created for that specific frequency. It could even be tied into a social function where a group of people might select to all move to a different frequency together and it, the decoding software, would follow them along. Perhaps the channel could monitor multiple less-active frequencies. That sort of stuff.

I think it would be a wonderful idea and think that good is just fine, and that I'd not expect perfection.

That said, I'm glad I'm not the only one that finds the place to be a time sink. I've spent more hours there than I care to admit. I favor the site that I linked directly, but that is mostly because that is the one I discovered first.

Depending on where you live, you can possibly also find local feeds from people's scanners. You can listen to the emergency responders, police, and things like that. It's not quite the same, but it is similar enough to where I figure I'll mention it. I don't usually bother with it, because I have a nice scanner already set up. Still, it is pretty fun. Also, if there is some sort of major event, you can go listen and hear what is going on before it is covered on the news. That's always fun.

The software for those WebSDRs can be found at http://strezhi.ru/temp/2015/websdr-dist11.tgz, might be an interesting project to add such features to it.

Though there is also OpenWebRX at http://sdr.hu/openwebrx, which does essentially the same thing but is more open source. It has some decoder plugins already.

You might enjoy this site:


Live chatter from Airports around the world.

You can use an audio pipe to decode signals with fldigi, however the occasional stuttering of the audio can mess up the decoding. It works better to use the record feature, then download the file and decode the audio from that. I've done Morse and rtty and psk and even some hamdrm and sstv images through the websdrs.

I have a Kiwi SDR here:

Also some scanner software:


Bookmarked, thanks. Are you going to add it to one of the indexing sites? What are your thoughts on decoding morse code with it?

It's on sdr.hu. I'll only do morse decoding the old fashioned way. That being said, things like CW skimmer are pretty amazing. I have a Flex-6500 and several Ettus SDR hardware, so don't use the Kiwi much.

I just lost 5 hours of my life to this website... thanks

I can understand that, and you're welcome. And I did warn you about it eating up your time. Before you know it, the dog has forgotten his name and your spouse has gone to Baja Mexico.

Meh, it's probably worth it.

Do not click the second link. No, don't do that. The second link is an index of other online SDRs. There are quite a few others and they are geographically disparate and offer different frequencies. Do not click that link! Do not bookmark that link! It is very, very bad for you.

I haven't tested these, but someone down the thread linked to some other software. By following that link, I found another site. That site, being evil, is an index for more online SDRs that use the other software.

You definitely don't want to click this link either:


I am going to make some lunch and then click that link. I'll do it so that you don't have to. I want to see what those radios offer and I want to see how well the software functions.

Remember, don't click the second link in my original post. In fact, you should probably burn your computer to the ground, it's the only way to be sure.

I've had enough computer for one day. I'm leaving the house.

You'll be back...

It really is addictive. It's a great way to experience part of what it's like to be a ham radio operator. Pretty soon, you'll be over at one of the ARRL sites, taking the practice exams, and applying for a test date.

Why yes, yes those keywords are unintentional. I wouldn't want you to go searching and find a new hobby, or anything like that.


I'd get a license but I'm happy just listening. It's already a time sink. I can't imagine what it would do to my free time if I actually had a way to respond.

Some of them do crazy stuff like use the moon for signal propagation... I'm not kidding. They will intentionally bounce signals off the moon, and do it successfully, to do two way communication. It's so common, they have a on acronym for it. They call it EME, Earth Moon Earth. Sometimes, they do it off Venus.

So, once you get the bug you can kiss your free time goodbye. But, you'll have a lot of new friends and be able to do cool stuff - including helping out in emergencies. Hams only provide communications, not actual rescues or anything.

Don't worry, you'll learn all about it when you join your local radio club. It's destiny, you might as well not fight it.

Wow. This kind of blows my mind. Thanks for the link!

It's nice hardware but as someone who moved to it from RTL dongles, there are a few problems:

- It's super complicated. There are an incredible number of configuration options and I don't know what most of them do. Documentation for them isn't great. Normally common settings aren't easy to find or use.

- Software support is limited. I don't believe I've ever had Gqrx working and though CubicSDR works, things like bandwidth selection in the UI are broken and I end up having to reset the board through the aforementioned complicated tools.

- As sold, it's useless for HF. You need to fiddle around with soldering/desoldering components on the board to make it do HF: https://myriadrf.org/blog/optimising-limesdr-matching-hf/

As a whole for me, it's been an unfortunately negative experience owning one. My RTL-SDR dongles and HackRF are much more useful to me because they Just Work™.

EDIT: I'm talking about the original LimeSDR. I didn't notice that this was the LimeSDR Mini, which I have no experience with.

Not sure why you would have any software compatability problems, the LimeSDR is supported as an gr-osmosdr device via SoapySDR (and driver=lime argument)

I wouldn't be surprised if this is even more constrained in terms of actual, unmodified usable frequency range since it has one RX channel with one input, as opposed to the two channels with three switchable inputs each on the original LimeSDR.

For HF have you looked at the upcoming airspy HF+? DC to 31 and 60 to 260 at 18 bit.


Only disadvantage is possibly the 768k max bandwidth.

Would you recommend BladeRF instead then?

The Bladerf is very easy to use. Good documentation. Pre-built binaries for the firmware and PC side APIs. I've used the C API extensively on Windows. Unfortunately as with pretty much all SDRs, the RF performance is pretty bad (spurious/images/etc). IIRC it has some odd limitations on the anti-aliasing filter and was quite CPU hungry at higher tx rates. You're not going to find an SDR without quirks though.

Better SDR gear is out there for a price: https://www.ettus.com/product/category/USRP-Bus-Series (these are their cheapest models)

I haven't worked with it so I honestly can't say.

Full duplex is such a big deal.

As an example, I have some remote controlled ceiling fans in my house. They're controlled by dumb RF remotes, but I wanted to make them smart so they can be controlled from Alexa.

Being a total SDR novice I figured it'd be easy to use an SDR to tackle this. But after much searching, I discovered full-duplex SDR is _super_ expensive. I think HackRF is the cheapest one at ~$500?

So instead I grabbed an RTL-SDR dongle and some dumb, cheap RF transmitters (the fixed frequency kind that you just dump a digital signal into) that had roughly the same frequency as the fan's remotes.

It only took me a day to get the RTL-SDR working, capture some of the remote's signals, and decode them. But when I tried to recreate the signals using the RF transmitter I grabbed they only worked 10% of the time. Maybe my timing was off. Maybe my antenna was cruddy. Maybe the frequency of the RF transmitter was too far off from the remote's. I felt intimidated by the big, scary black magic of RF. So I gave up.

I ended up just cracking open one of the remotes and soldering relays to all the button pads. An ESP8266 later and I can control all the fans in the house using Alexa. Not bad for a day's work.

But it would have been a lot nicer and cleaner to just use a full duplex SDR. Awesome to see something affordable finally coming out!

Doubt you would need full duplex there. I can't imagine that the fan had a transmitter or that the remote had a receiver. Even if they did, I would be really surprised if they were both full duplex radios.

HackRF is closer to $300, can transmit, but isn't Full Duplex. The LimeSDR (the original one) can also be had for around that price, and has two RX and TX full duplex channels, but not a whole lot of RF front end. HackRF would, however, work for the fan project.

you confuse Full Duplex with transceiver. RTL-SDR is receiver, hackrf is transceiver(receiving and transmitting, but not at the same time), lime is full duplex(can TX and RX at the same time).

You're right, I misspoke. All I needed was a transceiver (or even just separate TX). Regardless, you can't even get a SDR transceiver for an affordable price.

Why not use multiple RTL-SDRs?

RTL-SDR cant transmit.

I wish I could be more excited about this. I have one of the original LimeSDRs and it seems to have design issues. Mine has a massive DC bias that calibration doesnt seem to remove, and you can't actually use it for HF without desoldering a component. I feel like the Lime team so far has underdelivered for the hype.

This thing has awesome specs! Would it require much to turn it into an oscilloscope?

I guess it would require some frontend to get the voltages in the right scale and perhaps fancy overvoltage protection. Obviously you can do a lot better than 3.5ghz these days, but for audio and simple electronics it seems to be plenty.

Yeah, it would require quite a bit. Note that while it can input a massive frequency band (10M to 3.5G), the sampling rate is quite small (~31MS/s). Would work much better as a spectrum analyzer than a time domain viewer.

You can definitely use it as an oscilloscope, but it's non-trivial and has many limitations. Recommend getting a cheapo analog one, or if you're already at the normal SDR price range, just going for a Rigol

Just use your laptop's mic jack to make an oscilloscope.


Well I'd hope for a slightly better range than 20Khz and maybe resolution. Also I'd imagine the noise level wouldn't be very satisfactory.

With a 3.5ghz oscilloscope you could work on Mhz order chips, power supplies and who knows what other fun stuff.

I figured you were just looking for something to toy with. I figure that turning this device into a scope is not going to result in an accurate scope nor something that would be useful beyond entertainment value.

It seemed like a good idea to recommend something cheaper, easier, and better documented. Besides, who doesn't want to use their mic jack as an oscilloscope? ;-)

I started playing Watchdogs from Ubisoft about the same time I found out about the FBI’s Stingray devices. At the time I thought “at some point the tech for a stingray will be small enough to fit into a lumpy phone case. Then some enterprising hacker might be able to walk around pilfering people’s bank accounts like in the game.” I recognize the difference between MitM and penetration but follow me here... Somebody is already building a femtocell with these. What’s next?

Meh. We already had full femto on a carrier network compromised. They fit in a backpack and are easy to power on batteries. And we actually use them for full MiTM. It has been done in the field. Your concerns are reasonable.

Why use an annoying SDR and a flaky LATE stack when you can just buy and root a carrier femto? :)

Also, this is why you never use your real phone at DefCon/BH... Some joker's always have these going.

Anyone know if the FPGA code for the LimeSDR products is open source or tried to make modifications?

Is this a good way to get into SDR or is this device too much for a total beginner? I'm taking a telecommunications course later this year and this topic looks really interesting.

Maybe we shouldn't start using the `femto` prefix yet.

Cats already out of the bag on that one... The term femtocell isn't exactly new -- it's been used in the wireless world for some time now.

Ok, I'll be the first to coin attocell

Apologies asking a dumb question, but I am curious why you would say this...?

Not the GP, but... it has a specific meaning in the sciences:


I'd imagine the argument against using it is that it's being used in a less precise way. Femtocell is a name commonly used for a consumer-level device to extend a cellular network. One could argue that use of femto should have some bearing on the radio being used.

I misunderstood, and assumed femto refered to the board size, as compared to the original limesdr.

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