Getting Started With Software Defined Radio

In the last few months, software defined radio has seen an explosion in popularity thanks to a small USB TV tuner dongle able to receive anything broadcast between 64 and 1700 MHz. It’s a very neat project that opens the door to a whole bunch of radio experimentations, but getting started in the SDR world can be a bit daunting. To help everyone out, [MS3FGX] is writing a getting started guide so everyone can get into the world of software defined radio.

After getting one of the TV tuners supported by the RTL-SDR project (by far the most commonly used is this one from Dealextreme), the next thing you’ll need is a decent antenna. [MS3FGX] has had some success with this Radio Shack antenna, but it’s very easy to make your own.

The most popular software package to use with the RTL TV dongle is GNU Radio, and [MS3FGX] goes over the ins and outs of setting this up along with a brief aside for the Gqrx receiver.

After your hardware and software is set up, the only thing left to do is tuning into a few of your favorite stations. The range of frequencies the RTL covers includes AM and FM radio, along with GSM and GPS signals. Of course there’s a whole lot more you can do with this project like listening in on your car’s keyless entry fob, pagers, and wireless weather stations.

33 thoughts on “Getting Started With Software Defined Radio

    1. Do you mean the APT stuff around 137MHz, or the LRPT at 1691MHz? APT should be easy enough, although I already have a setup made out of an old scanner dedicated to this.

    2. Yes, I have heard of a few people receiving APT from NOAA satellites using RTL devices.

      The main thing is that you need a good antenna and precise timing, as you need to get the strongest signal possible.

      Also, RTL records in 8 bits, and most of the APT decoding software wants 16 bit, so you need to record the audio from Gqrx (or whatever you are using), then resample the audio at 11.025 kHz. You should then be able to feed it into APTDEC ( and get decent results.

      Getting NOAA sat images is one of my long term goals as I get more involved with SDR. At this point, I’ve been able to detect signals from some passing satellites with even the rabbit ears, but anything better than that will require a real antenna setup.

      1. I get decent (not perfect) APT pictures from a Uniden Bearcat portable scanner and a J-Pole (don’t laugh — it works).

        With the RLT-SDR and J-Pole, I can pick up NOAA Weather Radio voice signals on 4 of the 7 allocated frequencies with a bit of static — not quite as good as the Bearcat. Therefore, I wonder with the RTL-SDR if I would have to go an aimed yagi to pick up APT…

      2. ^I was wondering about the input sensitivity of these compared to “real” equipment, also. In my experience, TV tuner adapters don’t have as good of sensitivity compared to most digital TVs, so I wonder how they would compare to the frontend of a true scanner or radio. I wonder if an low-noise amplifier would help this, also…

        1. An LNA would certainly help with most satellite signals. At the least, it certainly wouldn’t hurt (unless the satellite just had an absolutely blaring signal strength, which most don’t).


    you have been mentioning SDR at least 3-4 times a week
    you are giving all the wrong people credits
    i hope you are doing this on accident

    first of all lets get this straight
    it is not balint
    to my understanding he stole the real peoples work
    goto ##RTLSDR on Freenode and talk to Patchvonbraum or Steve|m or m5sdos or something like that
    they will tell you the hole (REAL) story

    please someone get the hackaday guy to do this.
    im so tired of the guys who developed this not getting ANY credit at all

    1. Agreed,

      The real people working on this are Steve|m, m5dos(dos_fan]), prog, and a few others in ##rtlsdr on

      Basically what I’ve seen is balint and other people stealing code for their own personal gain in HDSDR and the extio. *Please give the others credit* and also realize that HDSDR is absolute garbage closed software. The devs even deny certain SDR transceivers to get TX support from HDSDR.

  2. The range of frequencies the RTL covers includes AM and FM radio, along with GSM and GPS signals. Of course there’s a whole lot more you can do with this project like listening in on your car’s keyless entry fob, pagers, and wireless weather stations.

    Well, starting at 64 MHz, the RTL dongle will not receive AM broadcast stations, but rather transmissions in Amplitude Modulation. VHF analog AM transmissions left are in the airband(s) or some public services in some areas of the world.

    Then, instead of listening to the bunch of data sent by RF remote controllers, a more clever way would be to try decoding it so that you can interface your weather station remote sensor and so on.

    Last but not least, if Coldplay are going to play somewhere near you, you could use RTLSDR to tune into their xyloband control frequency, take a few recordings and then share how to switch them on again… ;-)


      Probably because it’s used for:
      * Joint Tactical Information Distribution Systems (JTIDS) – Military and Government system utilizing spread spectrum techniques for terrestrial communication, navigation and identification

      The other systems I’m able to verify do not lie within the blocked ban. It could also be totally unrelated, just a coincidence.

  3. Interestingly enough, while I’ve been playing around with this I’ve found standard analog FM radio from much lower frequencies apparently being rebroadcast in the ranges of 840-855mhz. Anyone else able to confirm this behaviour?

    Unfortunately I don’t have any other gear that can read these frequencies directly, so I’m not sure if the dongle is messing up, or whether something is genuinely being broadcast at that frequency.

    1. I’ve seen something similar myself. I forget which frequencies they were on, but I was definitely getting faint rebroadcasts of FM stations well outside the FM range.

      Recently I’ve been looking into getting a cheap “real” radio that has at least some of the range of the RTL devices so I can verify a few of the things I’ve been finding.

      Like you, I can’t be sure if some of the odd signals I am picking up are real or due to glitches/limitations of the RTL setup.

  4. If you are hearing FM broadcast band signals around 932-940MHz you may be hearing the STL. Studio-Transmitter Link. Most radio stations don’t have their transmitters onsite. Rather, they have STLs to link the station. Though many are moving away from this method over to T-1s or, gaps, the public Internet, to ship the signal. Other places are around 150MHz & 450MHz for talk-back/in ear monitors for broadcast remotes. Enjoy listening.

  5. air traffic control radar signals are in the 1100-1250MHz range. I was thinking that it would be fun to pick up the transponder signals with this thing but I guess i’ll have to keep looking…

  6. Well lets see – got my EZTV645 stick + SDR#/Sharp
    and Lenovo notebook to for a portable Sdr rig and it was pretty cool..

    the EZTV645 v1.0 uses the fitipower fc0013 and was able to tun the entire range from 45mhz – 1000 Mhz

    in my area the RF signal pickens were soo piss poor, after connecting to a 10ft home brew Conical antenna for 10 – 1500 mhz didnt increase what i could get, it just improved the signal level of what i was able to recive.

    Playing with this sdr did have one benefit it saved me from spending 3500$ on a AOR 5000D wide band communcations reciver, to find out there nothing to much to hear.

    thanks hacka a day !!!!

    1. Where did you get the conical design, if you don’t mind my asking. I’ve been wanting to build one of those for awhile now, but haven’t gotten around to it. There isn’t a lot of build info available, at least as far as I could see.

  7. Oh by the way THE SDR was a very interesting experience despite the lack

    Since I purchased 2 of these 645 units I will proabbly attempt buiilding a RF down converter to extend the upper end to 2Ghz band,

  8. A broadband spiral approximately 24 inches wide should have acceptable enough performance at 137 MHz to receive the NOAA satellite broadcasts.

    Generally, if you want to lower the lower frequency limit of a spiral, a shorted ring around the outside at the same distance as the outer rim is from the next in arm will allow you to reduce its size by around 30% That should work with both archimedean and log/equiangular spirals. You’ll also need a balun to feed it but a cheap 4:1 TV balun made for matching a 300 ohm antenna to 75 ohm coax should work (assuming 50 ohm coax) at 137 MHz because the feedpoint impedence of most spiral designs averages in the 150-200 ohm range

    1. A FUNcube Dongle Pro+ would be a better choice for the 6m band. The RTL-SDR’s don’t handle the HF frequencies without a down-converter, and by the time you pay for one of those (which is bigger than the dongle), you could just as well get a FUNcube Dongle Pro+ which will do a heck of a lot more for you.

      And yes, either one will handle CW. If it will decode USB/LSB it will handle CW, but you might want to trim down the decoded frequency bandwidth to pick up one signal, or spread it out to see everything going on during contest weekends. But it’s easy to find software that will handle CW specifically.

      I hope that helps.

    1. I’ve got 3 personal favorites, any of which can usually be found on eBay or other sources:

      The Soft66RTL — an RTL-SDR with upconverter for tuning in frequencies lower than 50MHZ.

      The Soft66AD — a cheap SDR that natively can go between .5 and 70MHZ

      The Degen DE1103 – an inexpensive basic short-wave radio

  9. I know this is an old thread but the answer to many of the questions posted above is to take a look at the RSP from which goes below 24MHz – right down to Long Wave in fact. It also works well as a panadapter (hooking up to the 9MHz IF for example). It’s also becoming very popular for L-band working.

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