Tuesday, 22 May 2018

About Software Defined Radio and RTL-SDR


Software Defined Radio: computer or smartphone does signal processing, not individual and expensive components as with traditional radios. The cheapest way into radio reception, best bang for the buck.
RTL refers to chipset converting analog radio signal to digital form.
RTL-SDR dongles are digital TV tuners re-purposed for radio signal reception; with a special driver and free software, up to 2.4 Mhz worth of signals can be seen and heard - completely different experience than a traditional radio, where you only see and hear the tuned frequency. Think of looking at a waterfall through a telescope (Traditional Radio) or enjoying the whole scenery (Software Defined Radio).


Receive majority of human radio communications for cheap. Sky is not the limit; listening to the International Space Station orbiting 400 km above is an easy catch, plus more, popular uses:
- Listen to shortwave stations from other side of Earth,
- CB radio,
- VHF amateur radio,
- Broadcast FM, aka morning talk shows,
- Real-life weather satellite images as they come down from satellite, user image as an example,
- Voice of local utilities / security / taxi companies,
- Position reports from ships, trains and aircraft.
And so on, there are no gaps or locked frequencies with Software Defined Radio, no limit to what you can receive, hear, or decode.

How much?

Cheapest RTL-SDR receiver from China costs $8 from eBay, fantastic value if you're handy with wires for better reception. A better, and highly popular choice is rtl-sdr.com's V3 bundle ($27, manufacturer, usually sells out on Amazon fairly quickly), however, antennas in that pack are designed for indoor use only, and you'll get much better reception with an outdoor antenna. To Dad, friends or any acquittance I want to talk again, I recommend Nooelec's SMArtee bundle ($32, manufacturer, Amazon USA) for overall quality, 2-year warranty, excellent customer support, and most importantly, long cable to place either of three antennas indoors or outdoors.

Many other RTL-SDR dongles are available for specialist purposes and different budgets up to $50, you get what you pay for.

What about software?

Multiple choices, all free, popular for Windows 7, 8, 10:
- SDR Sharp, or SDR#, easy to use for beginners with lots of plugins for particular purposes,
- SDRConsole for an Office-like environment, if you use Excel or Word on a daily basis you'll feel home in no time,
- SDRUno, bit of a learning curve (my guide here) to get the most out of any RTL-SDR receiver.
Alternatives for Mac or Linux exists, I use neither platform, so aficionados comment below what's good.
Update: CubicSDR has been recommended by readers, download and webpage here.

What can I receive? How does it look like?

Frequencies between 27MHz and 1700 Mhz are yours for the taking with an $8 generic dongle, insert a wire in 3 minutes (called direct sampling) and get shortwave signals (below 30 Mhz). If you don't know what's a Megahertz, think of your car radio, that receives between 88 to 108 Mhz, so reception capabilities are enormous with any RTL-SDR.
User interface of SDRSharp for example, you'd only see 96.4 on a traditional radio:

See a signal represented by a hump or line (lots of different types out there), click on it, hear signal. Left hand side allows fine-tuning for better reception. Surely, procedure involves learning how to use a particular software suite, but nobody starts with writing macros in Excel straight away, isn't it?
Smartphone apps look more or less the same.

Complicated? How does it work?

No. A complete novice will get to "happy days" status in less than an hour, and that's a pessimistic estimate.
1. Install software.
2. Connect three components together: computer, dongle, antenna, then
3. Place antenna close to a window, or outside if you can. Nick a metal cooking pan from kitchen, place magnetic mount on that.
That's it, double click on software shortcut on Desktop, hear an invisible world.

Technical mumbo-jumbo

Complicated words such as impedance matching, wavelengths, ionospheric propagation, line of sight and so on are for enthusiasts, maybe you, definitely later on. Play with software, shorten or lengthen telescopic antenna, see what happens. If curious, google how radio signal reception works. Do your thing, exploring with success is the biggest reward.


No RTL-SDR can transmit, e.g. you can't talk to your buddy, mess up the neighbor's day by mimicking a car keyfob, or get in touch with buddy in Australia for $8. Skype, Viber, pick up the phone, get an UV-5R walkie talkie if wanna talk locally.
Some Software Defined Radios can transmit, we're talking many hundreds of dollars and in-depth software, programming and radio knowledge, sleepless nights of pure dedication.
If you really want to transmit, get in touch with your local ham radio society, easier and cheaper if you value your time.

I want to listen to the police, emergency services, firefighters

Not an easy task without some serious programming, and whilst it's apparently doable, easy and legal in the States, I have no interest, nor experience in the topic - what's the challenge with strong local transmissions anyway?
If police freqs keep you awake at night, you might be able to listen to them if they're analog, but most of the free world (drinkable water, McDonalds, careless walk home) gone digital ages ago. Not to mention, I heard from experience, emergency services are really boring.
If you're reading this from a less than fortunate region of the world where dictators reign, think twice, it's easy to end up on a lamppost, sent to a labor camp, or get stoned to death if you get caught.

WiFi, Bluetooth

No, RTL-SDRs are not WiFi or Bluetooth adapters.

I want to listen to cellphones or mobiles

Those frequencies are fully digital and encrypted, due to software limitations it's not really possible.

I want to receive digital TV

No problem, RTL-SDR dongles are primarily TV tuners, but due to different standards, the only RTL-SDR dongle which reportedly works in the USA is the ExCAP 645 - all others work for digital terrestrial TV, also called DVB-T, Freeview, Saorview, etc. Buy a $1 OTG cable and TV on an Android Smartphone is possible in less than 10 minutes:

Older (read: even $8 dongles) come with a remote.

I want to use RTL-SDR on my smartphone

No bother. Lots of apps exist for both Android and iPhone, visit your relevant platform store and search for "RTL-SDR", you'll be amazed.

I want to see aircraft position data.

You're not alone, called ADS-B, snapshot at my airspace as I write this, cheapest dongle with worst antenna on my windowsill indoors, can only get better than this:

Ordinarily, you get data of aircraft you can see with the naked eye with an $8 dongle straight away. If you want to reach out and increase range and data received, better gear is needed. I also love anything connected with aircraft, so this site has tons of info on ADS-B.

I want to listen to aircraft and pilot talk

Easy, specific frequencies for Tower / Approach / Ground can be found online within a minute, or seen in software without internet connection. For a taster how pilots and controllers sound like, go to the Live Air Traffic Control website.

I heard it's illegal

Receiving signals is tolerated in most developed countries as long as you don't act on the received information, to be on the safe side, ask around, read legislation, exercise common sense, or best of all, talk to local law enforcement. I've written extensively about the proper approach earlier.
Circumstances matter. Home town police did a courteous house call when I put a blatantly obvious huge antenna out on the roof, left within 10 minutes after being invited in seeing I'm a harmless radio enthusiast.
Update: Yours truly had college education on all aspects of radio, licensed to operate (including transmit) from HF to satellites, so it might be different when rozzers call. If in doubt, don't do it, better, get a licence from your local ham radio society, papers go a long way sizzling arguments with the law.
Please, do not use, operate or view any radio device in, at, near, or in close proximity to airports or aircraft without permission, unless you left home with the desire of four very twitchy policeman escorting your backside for a cavity search.

I got no money but want good receive performance

When I started all I had was $10 to spare and some free time, so had to go down the "make do" route. I still maintain, and deeply believe that money is not an issue, knowledge is. Having a slight clue what's happening from the very second radio wave hits the antenna to the joyful moment you see a transmission on screen has got more to do with the matter between your ears, not with equipment.
Order an $8 dongle, then in the two weeks until it arrives from Shenzen / Hong Kong: read, read, read. Speaking home, this page got lots of info, browse around, from easy mods to antenna positioning, or read posts on rtl-sdr.com, or google away. Reddit group is open to anyone, manufacturers lurk around helping as much as they can answering questions, RTL-SDR Facebook group full of helpful folks, all the info you'll ever need is out there. If stuck, comment below, I'll do my best to help if you have a question.

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