
LimeSDR Mini – An open, full-duplex, USB stick radio for femtocells and more - smokielad
https://hackaday.com/2017/09/22/cheap-full-duplex-software-defined-radio-with-the-limesdr/
======
KGIII
I get to recommend one of my favorite sites again.

[http://websdr.ewi.utwente.nl:8901/](http://websdr.ewi.utwente.nl:8901/)

You can also just go to [http://websdr.org](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.

~~~
gregsadetsky
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](https://en.wikipedia.org/wiki/Fldigi)]
does?

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

~~~
KGIII
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.

------
Veratyr
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/](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.

~~~
therein
Would you recommend BladeRF instead then?

~~~
stagger87
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.

~~~
seanp2k2
Better SDR gear is out there for a price:
[https://www.ettus.com/product/category/USRP-Bus-
Series](https://www.ettus.com/product/category/USRP-Bus-Series) (these are
their cheapest models)

------
fpgaminer
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!

~~~
rasz
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).

~~~
fpgaminer
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.

------
brian-armstrong
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.

------
tinco
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.

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

[http://www.instructables.com/id/Use-Your-Laptop-as-
Oscillosc...](http://www.instructables.com/id/Use-Your-Laptop-as-
Oscilloscope/)

~~~
tinco
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.

~~~
KGIII
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? ;-)

------
ryanmarsh
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?

~~~
bitexploder
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.

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

------
doppioandante
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.

------
traverseda
_Maybe_ we shouldn't start using the `femto` prefix yet.

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

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

[https://en.m.wikipedia.org/wiki/Femto-](https://en.m.wikipedia.org/wiki/Femto-)

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.

