
Ask HN: Looking to purchase a software-defined radio, any advice? - grantham
I&#x27;d like to use it to experiment with and explore interesting parts of the spectrum. For example: decoding digital television signals, seeing what my cellphone sends&#x2F;receives and how it encodes it, downloading weather satellite images, and so on.<p>I&#x27;ve no experience whatsoever in radio, only in software. Where should I start? What should I buy to begin with? Any general technical advice?
======
jrockway
The RTL-SDR is the default starting choice, because it's about $12. If you
find you don't like it, hey, you only spent $12.

I've used the FunCube Pro+ dongle for amateur radio stuff. It's very narrow-
band (it's based on a sound card as the ADC) but it does cover most of the
important amateur radio bands (HF) which most SDRs you find on the Internet do
not without additional hardware. It also has special filters around the 2m and
70cm amateur bands, the filters on 2m are especially nice because strong FM
radio stations tend to desense the cheap receivers here (RTL-SDR, HackRF
IIRC).

At work we use the USRP (B200) for WiFi-related testing, requiring the ability
to receive and transmit above 5GHz over 80MHz of bandwidth. The RTL-SDR is not
going to do that. (Actually the B200 doesn't quite cover 80MHz, but it's good
enough.)

For actual amateur radio work I use an Elecraft KX3 with the 2m module. You
can't beat the sensitivity of an entire system engineered to be sensitive.
With off-the-shelf SDRs (the KX3 is SDR-based) there are going to be a lot of
issues to debug to get the full system performing well. Fortunately, most of
the hard parts have to do with transmitting at higher powers, so you might not
care if you just want to listen.

A few friends have tried either the BladeRF or HackRF (I don't remember which)
and find that it uses an IF near the FM broadcast band, and hence they
couldn't get it to work reliably in Manhattan where they live because the IF
stages are desensed by the super-strong FM stations nearby. Of course,
debugging this is going to require already-working radios and test equipment
(oscilloscope/spectrum analyzer). So these cheaper SDRs are not off-the-shelf
instantly-working solutions. They're more of another thing that's helpful to
have in your lab. You probably don't want to tie up your $10,000 FTDX9000MP to
be a WSPR beacon, so you find a good-enough SDR instead and use that.

Finally, the good news is that most of the people writing software for the
radio experimentation community know radio and not software, so there is
plenty of room for improvement if you care to work on the software.

------
jlgaddis
I bought a "NooElec NESDR Mini 2 USB RTL-SDR & ADS-B Receiver Set" [0] from
Amazon a few months ago. It worked without any issues with both Linux and OS
X.

I've had a ham radio license for a little over 21 years so I've always been
interested in radio but the whole SDR thing is new to me. I still really
haven't done a whole lot with it but it's fun to play with.

The neatest thing I did was set it up on the balcony of our 23rd floor condo
on Panama City Beach (facing the Gulf of Mexico) and used _dump1090_ [1] to
plot aircraft locations (using ADS-B) on a map. I was able to "see" planes a
few hundred miles away (thanks to the height and facing out over the water)
but was also able to see them at pretty much ground level.

I have access to a bunch of buildings (mostly on top of big hills) across the
southern portion of Indiana thanks to my job and have been thinking about
building a bunch of "ADS-B receivers" (using Raspberry Pi's or similar) and
putting them out in these buildings so that I can cover a wide area. (I really
only probably need about three as long as I put them in the right locations,
geographically speaking.)

 _Edit: I do need to find a good external /outside antenna designed for 1090
MHz, if anyone has any firsthand recommendations._

In addition, at one of these locations there's a communications tower used by
a pager company to transmit pages so I've thought about building a POCSAG
receiver with one of these devices as well.

Unrelated to SDR, but I'm also planning on putting together a bunch of stratum
0 NTP servers (using GPS) and deploying them at these same locations as well.
They will primarily be for my own use at work (ISP) but I expect to make
publicly available a few stratum 1 servers as well.

[0]: [http://amzn.com/B00P2UOU72](http://amzn.com/B00P2UOU72)

[1]:
[https://github.com/antirez/dump1090](https://github.com/antirez/dump1090)

~~~
sandworm101
Tracking aircraft with a passive radio receiver? You just sold me on SDR.

~~~
sokoloff
It's ADS-B-[1], which has some limitations (don't imagine you're getting every
target, etc), but it is damned cool nonetheless.

[1] -
[https://en.wikipedia.org/wiki/Automatic_dependent_surveillan...](https://en.wikipedia.org/wiki/Automatic_dependent_surveillance_%E2%80%93_broadcast)

------
mng2
Definitely the first step is to get a cheap USB dongle. There is a RTL-SDR
compatibility list[0] that you may find useful. Once you play with a cheap one
you'll have a better idea of the parameters you can improve by upgrading to
more sophisticated/expensive hardware.

0:
[https://www.reddit.com/r/RTLSDR/wiki/compatibility](https://www.reddit.com/r/RTLSDR/wiki/compatibility)

------
forgotpasswd3x
There is a SDR subreddit that has a wiki with some info. I had it bookmarked
from a while back when I was looking into purchasing one, however that's
something I've put on the back-burner for now.

[https://www.reddit.com/r/RTLSDR/wiki/index](https://www.reddit.com/r/RTLSDR/wiki/index)

------
blkhawk
If you went to the CCC camp this summer in Germany you could have gotten a SDR
with your badge.

The badge [0] (called rad1o) is a hackrf-compatible SDR for frequencys between
50 and 4000 mhz.

Maybe somebody at a local hackerspace went and is willing to trade you his?

[0]: [https://rad1o.badge.events.ccc.de/](https://rad1o.badge.events.ccc.de/)

~~~
mappum
+1 for the rad1o/hackrf. Most of the other SDRs people are recommending here
are only receivers, so they can't transmit.

When I was at CCC camp I made node.js bindings for the hackrf, so it's pretty
easy to work with: [https://github.com/mappum/node-
hackrf](https://github.com/mappum/node-hackrf),
[https://github.com/mappum/hackrf-stream](https://github.com/mappum/hackrf-
stream)

------
blueintegral
Whether you get a USRP or not, the Ettus Research bootable image has GNU Radio
already installed and configured, as well as a bunch of other useful radio
tools:
[http://files.ettus.com/liveusb/latest/](http://files.ettus.com/liveusb/latest/)

They've also got some good tutorials on using GNU Radio Companion.

I'd recommend an RTLSDR, USRP, or HackRF. All good, all different price range,
and all have a good community and support around them. If you're interested in
a particular band, you may want to get an antenna for that band as well. Ettus
Research sells some antennas, or you can buy one from an amateur radio store,
or build one for very cheap from the dozens of plans out there by ham radio
operators.

------
jaredharley
I bought a cheap SDR off of Amazon that I've been happy with:
[http://amzn.com/B00D3GRU24](http://amzn.com/B00D3GRU24)

I started with listening to NOAA weather stations[1], and now I'm tracking
aircraft with PiAware[2]

[1]: [https://jaredharley.com/2015/08/25/software-defined-radio-
sd...](https://jaredharley.com/2015/08/25/software-defined-radio-sdr)

[2]: [https://jaredharley.com/2015/08/31/tracking-aircraft-with-
pi...](https://jaredharley.com/2015/08/31/tracking-aircraft-with-piaware)

------
Bouncingsoul1
If you care I live in Berchtesgaden, which provides the unique feature of
testing the Galileo System upfront [http://www.gate-testbed.com/en/gate-
overview.html](http://www.gate-testbed.com/en/gate-overview.html) . Anyway
after learning the ESA even has a StartupIncubator here. Because of this,I
decided to give it try. My first goal is to build a receiver based on the
Raspberry Pi,no idea if i have a chance of doing this, I downloaded the specs
and will give it a shoot and see where I get from there.

------
ChuckMcM
So you can start small and grow, or start large and be overwhelmed :-) The
"low end" are the various DTV tuner sticks and NooElec is a good source for
them. The middle of the road is the HackRF One ($300). The high end would be
something from Ettus Research like the USRP.

I have one of the USB DTV receivers and it was fun for exposure but hard to do
really interesting stuff with. I got the HackRF One and it has been a lot of
fun, I added the Ham-it-Up so that I could easily play around in the HF and AM
bands. For my bluetooth work I ended up getting an UberTooth even though the
HackRF One should be able to do what I need, the Ubertooth was more compact
and simpler to set up and take down.

In my case I'm interested in mesh network wireless systems for robotics and
room / house localization for those robots. I also have one of the newer
Crazie Fly quad copters and want to get to the point where I can manage it
using software.

The important thing is to pick a unit that can operate in the frequencies you
are interested in (the HackRF One goes 1Mhz to 6Ghz so its pretty wide open)
and be ready to revisit a lot of math you might have considered less than
useful back in school (complex numbers).

Really though maximum value per $ is probably though starting with one of the
USB DTV receivers. If you find you hate it, or its too steep a learning curve,
then you won't be out all that much.

------
colsandurz
In general Ettus is the best around unless you have a really large budget and
want to get something with a backplane (which I highly recommend you avoid
unless you have really specific requirements). Ettus is about to come out with
a low cost B200 mini which could be a good option. I think it's so they can
compete with the BladeRFs and HackRFs of the world. Ettus boards aren't
perfect but they've really come a long way since the USRP2 days when I started
using them. The UHD is also a really nice library to work with.

The RTLSDRs are definitely the best value (get one with a metal box around
it). Also look for the HackRF Blue.

Finally, think hard about what you want to do. You mention decoding TV signals
but the RTLSDRs can't do that (in America at least) since they can only do
about 3 MHz of instantaneous bandwidth and TV signals are 6 MHz wide. You
could try using 2 or 3 RTLSDRs for that but then you'd have put them all on
the same clock, which can be difficult.

If you can spend around $1500 I'd go for a B200 with a GPSDO. GPSDOs let you
accurately timestamp signals and time evens (i.e. start transmitting at some
specific time). In my eyes the 210 isn't worth the bigger FPGA and dual
transceivers. The isolation between the transceivers probably isn't great (but
I could be wrong) and a bigger FPGA isn't worth anything to me.

------
Veratyr
A lot of people are recommending Nooelec but I'd recommend starting out with
the RTL-SDR blog SDR. It'll have a low PPM receiver and an SMA connector. A
lot of the cheaper RTL-SDRs you get (including Nooelec) can have high PPM, non
TXCO oscillators. If you're working with weak signals it can kill. There's
software to allow you to tune the SDR and eliminate the PPM error but most of
the oscillators with high PPM vary by temperature so if you have the SDR in
different or changing environments, your calibration can cease being accurate.
The SMA connector is a huge help with antennas because the built in MCX
connector on many of the SDRs can be pretty fragile (I've broken a couple by
accident so far). If you do get a Nooelec anyway, get one of the 0.5PPM models
(I think they call them "Mini 2+" with the "+" on the end).

If you like the RTL-SDR after playing with it a while and have a bit of money
($300) I'd strongly recommend the HackRF One. I only started with SDR a few
weeks ago and the RTL-SDR was great (especially for the price) but the HackRF
One is a whole other level. The amount of bandwidth you can get out of it is
amazing.

If you're hoping to handle weather satellites and such, you'll need to build
your own antennas. They can be kinda big and you'll need line of sight to the
sky most of the time so it'll work best if you have a large open area you can
frequently visit. If you own a house your back yard might be good. If you're
in an apartment building the roof or parking lot is probably best.

Something else that's fun to play with is ADS-B. It allows you to pick up air
traffic position/altitude/speed/heading broadcasts.

------
pdx6
I just started playing with the HackRF
([https://greatscottgadgets.com/hackrf/](https://greatscottgadgets.com/hackrf/)).
The inventor has a bunch of great video tutorials to walk you through all the
tools and how they work, starting with analog and then focusing on digital.
You can use OSX, Linux, etc. with the tutorials.

------
as1ndu
As an introduction to signals, The Scientist and Engineer's Guide to Digital
Signal Processing is pretty good([http://dspguide.com/](http://dspguide.com/))
you should also read this woman's blog
[http://www.windytan.com/](http://www.windytan.com/)

------
krapht
Start with an rtl sdr dongle. Upgrade to USRP when you get more serious.

------
pbhjpbhj
Saw this -
[https://www.youtube.com/watch?v=R-2k6TMPMRo](https://www.youtube.com/watch?v=R-2k6TMPMRo)
\- a while back from a Finnish hacker, partly concerned with hacking bus-stop
signals. IIRC it gave good details on her process and some info on the tech
used.

------
lormayna
You can buy an RTL-SDR key, un upconverter to receive also the shortwave, a
notch filter to cut off radio broadcasting that may saturate your receiver and
a good multiband antenna. The whole kit will cost around 100€.

------
Cerium
Get an RTL-SDR stick. There is such a community around this hardware that you
can be up and running in a few minutes after it arrives.

I purchased a "RTL-SDR Blog R820T2 RTL2832U" a month ago. It has an upgraded
oscillator (less setup hassle) and comes with a usable antenna. In the Bay
Area I've been able to listen to FM radio, NOAA weather, SJC Airport tower,
Police - both NFM and digital, and ADS-B.

I'm quite happy with the purchase, and excited about the possibilities of what
I can do next.

------
zacman85
You should check out the Whitebox Software Defined Radio Project. It is a
hacker friendly software defined radio started by my friend Chris, a former
lead engineer from Google/YouTube and the former VP of technology at Adly.
[http://radio.testa.co](http://radio.testa.co)

------
go1979
I got a USB dongle that seems to work under 1GhZ. I was really interested in
analyzing zigbee. I think that's in the 2.4GhZ ISM. Any suggestions?

I'm also curious ... are these cheap USB dongles just receivers? Or do they
have ones that can transmit as well (i.e. transceivers).

~~~
jimmcslim
You definitely can get SDR transceivers but 1) they are more expensive and not
(to my knowledge) 'dongle' sized, and 2) in most jurisdictions there are
understandably licensing conditions required in order to be permitted to
transmit on the amateur frequencies.

If anyone with experience on SDR transceivers has some input here, that would
be great!

------
lightlyused
I've been looking at this one: [http://www.wimo.com/dx-patrol-sdr-wide-band-
receiver_e.html](http://www.wimo.com/dx-patrol-sdr-wide-band-receiver_e.html)

------
bronz
Whatever you get, make sure you have an antenna lined up for it. It's
completely useless if it does not have an antenna. And many of these dongles
use weird antennas that you can only get online. So mind that.

------
cagey_vet
rtl-sdr for the win, i can talk about this stuff all day long. now for the
software part, with windows systems, options are plenty. linux, hit and miss.
gnu-radio is a lofty suite, but here for me, its gqrx. building your own
antennas can be quite fun. i typically craft something every month or so,
depending on my obsession at any given time, aircraft, satellite, amateur.

i also buy commercial grade hardware., as rtl-sdrs can be a little dodgy due
to low tolerace components, so weak signals are hard to digout of a sound
floor with cheapo dongles.

------
lovelearning
Hackaday ([http://hackaday.com/](http://hackaday.com/)) often has new articles
on DIY SDRs. Good way to learn.

------
geeknik
SDRPlay
[http://www.hamradio.com/detail.cfm?pid=H0-014408](http://www.hamradio.com/detail.cfm?pid=H0-014408)

------
efftee
Lots of interesting ideas and hardware advice on [http://www.rtl-
sdr.com/](http://www.rtl-sdr.com/)

