the most fun $12 gadget ever- rtl2832+r820t USB software defined radio dongles - Page 1
Forum section: electronics / general

author: cdev
author_rank: Super Contributor
timestamp: January 28, 2015, 05:49:42 am
content: Hello, I am surprised I have not seen these discussed here. Certain RTL2832U chipset based DVB-T dongles sold in much of the world for almost nothing, basically around $10-15 - for watching DVB-T digital TV, were discovered to work as software defined radios in a sort of test mode around two and a half or three years ago.(a common nickname is "RTLSDR" or "rtl-sdr" )Seehttps://sdr.osmocom.org/trac/wiki/rtl-sdr- that is the main site for the rtlsdr software where you can download the drivers for linux and windows directly, on Mac OSX you can compile the Unix drivers from source using the same instructions as for Linux or install librtlsdr, gr-osmosdr, gnuradio and gqrx from macports.. gqrx (http://gqrx.dk) also has a drag and drop installer that installs the gnuradio libraries on OSX.. good for a quick start, macports is better for seasoned users. two good Windows programs you can use with them are athttp://hdsdr.deandhttp://sdrsharp.comFor support, there is a forum athttps://www.reddit.com/r/RTLSDRits a good starting point for beginners..they are a real phenomenon..Their sudden and quite unexpected discovery has basically kicked off a lot of interest in SDR around the world, because they really are such an extraordinary value.They make a very decent radio for receiving almost anything that will fit in up to around a 2-3 MHz slice of spectrum from roughly 25-1750 Mhz. (typically around 2.6 Mhz without any dropped samples, and up to 3.2 MHz on a good day - if you don't mind occasional errors and sudden quits- that ability is great for doing screenshots on a lightly loaded machine.)Thats really an engineering marvel, given the size (smaller than your finger) and cost (less than the cost of a good movie for most people, including shipping)What else can be done.. really, a hell of a lot.. you could use them for teaching DSP, a number of schools do exactly that.. FM radio on them works great, you can also receive stuff as diverse as weather satellites, public safety transmissions, GPS (with a bias tee and an amplified GPS antenna) ADSB ) aircraft tracking signals) AIS, the list just goes on and on.. and even shortwave (with an HF upconverter or direct sampling).. radio astronomy, and so on.. You can receive all sorts of digital modes.. as you can see from the long list of compatible applications on the osmocom site, also Gnuradio - basically a tool kit for writing radio applications which run using a combination of C and python code.. in a notebook style format..has several dozen pre-made apps.. (http://Gnuradio.org) is a development environment "gnuradio companion" or GRC with which you basically connect signal sources and functions and sinks with signal path lines, just connect them with the lines.. and doing this you can literally prototype almost any kind of radio system with drag and drop on a screen, then you compile them and zap, after a bit of tweaking, they work! Its serious radio fun, a very powerful tool and you also learn a lot very fast. they are also so cheap you can give your boisterous kids, (co-workers, etc.) one and not worry if it will get broken.. (although i would recommend getting several both for backup as one never knows how much longer they will be around)They make good IF stages for dedicated task specific radios, and they are so small they can be mounted right at the antenna feed point and fed using a USB extension instead of coax. No other radio i know of can do that.Some important things to remember..otherwise you might never get it working as it should and get frustrated and give up which would be a tragedy because they almost always work great once you learn their quirks..1.) the supplied antenna is worthless, and the "coax" connecting it isnt even coax, its microphone wire..Don't use it. Buy an adapter when you buy the dongle (or better yet buy several) so you can use yours with BNC, SMA, F, etc..2.) Use a USB extension, a good one - and a bunch of snap on ferrites - 2 minimum, but preferably more. Also put some on any nearby RFI-producing devices, like monitors, etc. Use the longest USB extension you can if you need to get the device away from your computer (which generates a lot of RFI crap).. which more likely than not will not show up on your screen it will simply desensitize your receiver and you will think its broken.. thats a quirk they have.When you add ferrites the signal will magically come out of the noise..3.) Use a good antenna, it can be home made.. for example, here is a good very simple ten minute antenna you can make out of two dollar store pizza plates and some coax. You can use RG-6, CATV coax..http://www.wa5vjb.com/references/PlanarDiskAntennas.pdfThere are roughly 6000 videos on youtube about various things one can do with them. You can do hundreds of different things with them. feel free to PM me, I know a fair amount about them and have helped get a lot of people started with them.They would make a great subject for a show- or even several shows, as they literally are one of the most fun and flexible and cheap electronics devices out there, they must win some kind of prize for incredibly high value for money, as they can in many cases do things that otherwise would require very expensive radios to do.They have sort of kicked off a huge amount of interest in software defined radio around the world, including in Australia. For example, as you can see in the image below, ( and also at SM5BSZ.com ) they can be used as a quite functional very low cost spectrum analyzer.. the ADC chip in them could also be used for other kinds of sampling, I bet. To make lots of super cheap test equipment that perform surprisingly well considering its very low cost and extremely tiny size.Anyway, the search string rtl2832+r820t on ebay will bring up a bunch of them. The one in the image below is a good choice, as it has a slightly better crystal than most of them, (more accurate and less drift) as well as a robust, durable PAL style antenna connector and what has proven in my experience to be a very sensitive receiver.Make sure whatever you buy has an RTL2832 and a R820TI've attached an image of a approximately 3 Mhz slice of HF (shortwave) spectrum, captured using a long wire antenna and an up-converter. It samples at 8 bits so its not as good in some respects as some much more expensive SDRs but for the money it really is pretty amazing. Each one of the lines in the attached PNG picture is a signal. It can record all of this spectrum to disk at the same time if that is what you want.. (that eats up a lot of disk space very quickly) They also make excellent FM radios. You can see 2.5-3 MHz of spectrum as you listen.. so you learn a lot about radio by tuning around..Anyway, highly recommended.

author: jeremy
author_rank: Super Contributor
timestamp: January 28, 2015, 08:30:06 am
content: Cool! I have played with these a little, but not really in depth. What software is in your screenshot?

author: rdl
author_rank: Super Contributor
timestamp: January 28, 2015, 02:24:00 pm
content: I bought one of these several months ago. They work pretty well, but do seem to pick up a lot of noise. I have a USB extension cable and I bought a small metal box to put it in, but when the box arrived it was too small. I have another on order.I've been using SDR# and ADSB#/adsbscope for software. For now, I've got it hooked up to an old CB antenna, because I have it and it's already set up and mounted outside. It really needs something better than that.I bought the stuff to make one of those coaxial-colinear antenna for ADS-B but haven't had time to actually assemble it.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 28, 2015, 02:48:30 pm
content: Just another site to keep an eye on (and/or the twitter account), a lot of info for this device:http://www.rtl-sdr.com/

author: xrunner
author_rank: Super Contributor
timestamp: January 28, 2015, 03:02:12 pm
content: Yea they're fun. I've had a setup for a couple of years. The dongles are dirt cheap off Ebay from China. I use them as a pan adapter for the ham bands, but you need an up-converter because as you said they won't go below 25 MHz or so -http://www.nooelec.com/store/ham-it-up.htmlBut yea it's a good toy to have around.

author: 128er
author_rank: Regular Contributor
timestamp: January 28, 2015, 03:29:17 pm
content: Have one too. I can highly recommend this. I'm not very into HAM or something, but for the price of this sticks, it is worth to play with it.Very interesting to track planes with ADSB-Scope

author: cdev
author_rank: Super Contributor
timestamp: January 28, 2015, 10:18:06 pm
content: Jeremy, its an old version of SDR#.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 12:42:01 am
content: I have one. I got it a few months ago for about $20 on eBay.I didn't have much luck, got a few signals but was unimpressed. I'll have to try to make my own antenna like you said, and also going to try the ferrite too since I never did that, maybe it will help. Thanks!

author: mazurov
author_rank: Frequent Contributor
timestamp: January 29, 2015, 01:43:02 am
content: They are also good to receive sensors, like ones in electricity/water/whatever meters, as well as wireless thermometers, weather stations, etc. The accuracy of internal crystal is pretty bad though and good crystals to replace it are rare, I'm lucky to have WWV nearby :-).

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 01:56:24 am
content: That ham-it-up thing is quite expensive. I tend to think an oscillator + diode-ring mixer + filters would do the job.$10 + solder, maybe.

author: nowlan
author_rank: Frequent Contributor
timestamp: January 29, 2015, 02:28:27 am
content: The crappy aerial and adapters required put me off buying one of these earlier. I am not familiar with the pieces.Plus the added cost of the up converter to listen to ham.Was hoping the hackrf stuff comes down, such as thehack rf blue, or even revision thereof.In the meantime my dad is streaming internet radio.

author: cdev
author_rank: Super Contributor
timestamp: January 29, 2015, 02:29:38 am
content: I would definitely give it another shot with a USB extension, some ferrites and another antenna. the PC noise makes the signals just fade into nothing and people think they are broken. And you don't even see signals. its some particularity of the fairly sophisticated internal tuner..Just to see how it works, as a quick experiment, try taking the little antenna, putting the magnet on something metal.. and clipping a meter or so long wire to the little screw thats revealed when you remove the little antenna whip. When i say let it stick to the top of a metal object I mean everything except for your computer.. a cookie plate is good.. or a metal tray or whatever..Don't take off the side of your computer case, that will make noise worse.Quote from: codeboy2k on January 29, 2015, 12:42:01 am

author: xrunner
author_rank: Super Contributor
timestamp: January 29, 2015, 02:54:00 am
content: Quote from: cdev on January 29, 2015, 02:29:38 amAnother trick - the USB dongle doesn't have to benearyour computer as it would be if you just stuck it into a USB slot. i.e., get yourself a long USB extension cable and put the dongle as far away from the PC as you can.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 03:01:10 am
content: Quote from: dannyf on January 29, 2015, 01:56:24 amJunk box parts and a signal generator from my bench for the LO. I'd definitely do it that way too. I wouldn't want to buy the up-converter, because listening to the ham bands is not something that I have a lot of time for and no need to buy a nice board when I can hack it togetherQuote from: xrunner on January 29, 2015, 02:54:00 amThanks, I'll try both those suggestions. When I tried it, I actually did plug it straight into the front USB port since I don't have a USB extension handy. And my PC is always open case these days, but it doesn't need to be anymore. I had a Lattice ECP3 there before.

author: picandmix
author_rank: Frequent Contributor
timestamp: January 29, 2015, 11:13:46 am
content: Forgive the most basic question, but rf is not my area though this little devices do sound interesting.Looking on Ebay UK there seem to be 2 main types, the white one Cdev mentions in his opening post and the others are small black units marked DVB-T like this one.http://www.ebay.co.uk/itm/Hot-RTL-SDR-FM-DAB-DVB-T-Dongle-Stick-RTL2832-R820T-SPC-0155-/350740732224?pt=UK_Computing_Video_Capture_TV_Tuner_Cards&hash=item51a9c6d940Now the in the detail of the black ones it does say its ok for UK use though not in the US.The white one I have seen does not specify any region.Other than them clearly stating in their adverts, how can I tell which units will work properly here in the UK ?

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 29, 2015, 11:27:41 am
content: Quote from: picandmix on January 29, 2015, 11:13:46 amThe black one is fine too, my guess is that the region stuff has something to do with the DVB reception which you are not going to use anyway.

author: VK5RC
author_rank: Unknown
timestamp: January 29, 2015, 11:39:21 am
content: If anyone is serious re good SDR these guys have been working hard for 7-8+ years or so but the gear is not cheap but outperforms most high level receivers.http://openhpsdr.orgorhttps://apache-labs.comAnother popular Ham SDR but not quite so good as above ishttp://www.funcubedongle.com

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 11:50:00 am
content: QuoteYou could then use the generator to tune the radio,The upconverter should be easy to build, especially if you go with an active mixer (602/612 for discrete).

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: January 29, 2015, 12:31:09 pm
content: A lot of fun.Throw away any indoor antenna it comes with - an outdoor antenna is essential. A discone or 2m/70cm ham antenna is fine.Mine is a bit deaf but you'll hear 88 - 108 MHz FM stations, aircraft around 120 MHz, 2 metre & 70cm repeaters, analogue FM two way radio and more. You'll also see digital TV signals appear as rises above the noise.HF upconverters are easy to build and most worthwhile. With an outside antenna you'll hear broadcasters, time signals, hams and more from around the world. Either make one based on an NE602 or VHF oscillator module (eg 50, 66, 75 or 120 MHz) + 4 diode mixer.An example of the latter ishttp://www.george-smart.co.uk/wiki/FunCube_UpconverterGood, simple and cheap. Though if you can it's better to have an IF out of the FM broadcast band to avoid noise due to bleed through.

author: albert22
author_rank: Regular Contributor
timestamp: January 29, 2015, 05:58:00 pm
content: Take care when using an external antenna. Some dongles don't have input protection diodes and could be damaged by spikes or static.http://www.reddit.com/r/RTLSDR/comments/tl187/tuner_protection_diodes/

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 08:15:57 pm
content: Quote from: dannyf on January 29, 2015, 11:50:00 amYeah, the generator would tune it, could maybe do a better band sweep to. almost sounding likeI don't have a 602 in my junk bin (maybe I do, I'll have to keep looking). But I do have diodes and transformers readily available, so it's easier to start with a diode mixer.If the performance is not there, then I'll go active. Until I get a better antenna, usb extension and close up my PC I got nothing anyway

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 08:30:20 pm
content: The funcube upconverter linked earlier would be what I would do, though with a simpler low-pass filter.

author: xrunner
author_rank: Super Contributor
timestamp: January 29, 2015, 10:53:41 pm
content: The little dongles were meant to watch TV on your PC, funny I've never even used one for that!

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 11:00:11 pm
content: Quote from: dannyf on January 29, 2015, 08:30:20 pmI get Service Unavailable when I go to the funcube web site so I'll have a look later to see what they've done with their up-converter .Thanks for that tip.Since I'm experimenting, I want to take baby steps, and improve it if I need to.To start, I was just thinking of a simple common diode mixer:This needs a bandpass filter at the IF out, and a lowpass at the RF in (the antenna), and maybe some additional filtering at the LO in.Here's where I wish I had some nice tunable filters on my bench that I could just hook upAnd here's a complete circuit with a 602, and a 100 MHz LO . This one is screaming to be done Manhattan style

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 11:15:19 pm
content: QuoteThat can be simplified by either using an outboard oscillator (or a sig gen), or utilizing the built-in oscillator + the 100Mhz crystal -> which is actually quite rare.

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 11:21:29 pm
content: Here is the funcube up converter.It is almost perfect. Deadbug would be great.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 11:49:51 pm
content: Quote from: dannyf on January 29, 2015, 11:15:19 pmYeah, I didn't know why that circuit was using it's own LO circuit, the 602 just needs the external crystal.If I built it up I'd start with my sig gen as the LO anyway, and if I used a crystal on board , then I'd just use what I had and let the IF fall where it may, it's not important for this application, as long as it lands in the usable range of the dongle.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 11:52:02 pm
content: Quote from: dannyf on January 29, 2015, 11:21:29 pmIt looks basically as we've described, diode mixer with filters. Simple.Thanks for that. good to have it in the forum as a reference too .The site is back up for me now.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 11:55:25 pm
content: almost perfect. If it works as it is then good, but I'd probably want to add a bandpass on the IF output

author: dannyf
author_rank: Super Contributor
timestamp: January 30, 2015, 12:22:24 am
content: Either low pass or high pass alone would work.Yes, otherwise, you can get mirror images of the stations.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: January 30, 2015, 09:14:40 am
content: Quote from: codeboy2k on January 29, 2015, 11:49:51 pmOne of the benefits of using an external crystal oscillator (instead of the internal one in the NE602) is you can filter its output so that only a 100 MHz signal is presented to the mixer. That lessens the chance of image signals causing interference. As an example, I tried a downconverter using a 50 MHz crystal oscillator module with little filtering. When I tuned the SDR to 101 MHz you could hear AM broadcasters at 1 MHz due to this lack of filtering (mixing occurring with the harmonic of 50 MHz).I would also be wary of using 100 MHz as a crystal frequency unless shielding is very good or you don't have strong local FM stations. Breakthrough increases noise and lessens clarity of the HF signals you're trying to pick up. And you can sometimes even hear the FM stations in wide FM mode whereas on narrow modes they just come up as noise that's not easy to tell as breakthrough.Depending on how low your dongle tunes an oscillator frequency of maybe 60 MHz, or maybe 110 - 120 MHz is probably ideal as signals in those segments (and 30 MHz above) aren't as strong or wide in bandwidth as FM broadcasters.

author: janoc
author_rank: Super Contributor
timestamp: January 30, 2015, 10:35:03 am
content: Quote from: cdev on January 29, 2015, 02:29:38 amYou mean the AGC turning down the gain when the front-end gets overloaded with RFI?That's a bog standard feature in radio receivers

author: han
author_rank: Frequent Contributor
timestamp: January 30, 2015, 12:10:54 pm
content: I just Buy and test.Quick setup:1. Download SDR sharp (IMHO the best software for SDR)http://sdrsharp.com/#download2. Do not install any driver or software from the Dongle3. Usezadig.exe from SDR sharp to install driver.4. DONE

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: January 30, 2015, 12:20:14 pm
content: Quote from: han on January 30, 2015, 12:10:54 pm5. Set up a good VHF outdoor antenna (eg groundplane fed with coax cable >5m above ground)6. Start by scanning the FM broadcast band.7. Then experiment with other modes - eg NBFM on VHF/UHF and AM on airband.8. Experiment with gain and AGC controls. And filters and bandwidths. Sometimes they will have a big effect.

author: Shock
author_rank: Super Contributor
timestamp: January 31, 2015, 12:44:18 am
content: Any dongle (usb tuner) recommendations with hardware comparisons (or links to these)?Which models currently being sold have input protection, better crystals, compatible, superior antenna sockets, great usage flexibility?