QRSS: Radio amateurs’ slow-speed narrowband

qrss

Host of the Soldersmoke podcast, [Bill Meara], contributed this guest post.

While the rest of the world is moving toward high speed broadband, some hams—including one Nobel Prize winner—are going in exactly the opposite direction. Our ‘QRSS’ mode makes use of an unusual mixture of modern digital signal processing (DSP), ancient Morse code, and simple homebrewed transmitters. Very narrow bandwidth is desirable because this reduces the noise in the radio communication channel, greatly improving the S/N ratio.  But Shannon’s communication theory tells us that narrow bandwidth comes with a cost: slow data rates. In QRSS, beacon transmitters using only milliwatts churn out slow speed Morse ID signals on 10.140 MHz that are routinely picked up by DSP-based receivers on the other side of the globe. Many of the receivers, ‘grabbers’, have visual outputs that are available online in real time. QRSS has been getting a lot of attention on the Soldersmoke podcast and on the Soldersmoke Blog. For more information check out this overview and the hardware involved. Here’s a gallery of received signals.

Comments

  1. sorry, don’t get it

  2. rick says:

    it’s not necessarily useful to everyone, but this means, from what I understand, that you can have a signal broadcast at very little power consumption across the world, however it will be at a relatively very slow rate. What uses this can be used for specifically, I cannot say, but it is pretty neat anyway.

  3. joe57005 says:

    This will be of tremendous use when the internet goes down during the inevitable zombie apocalypse.

  4. vic says:

    Apparently someone is emitting a signal such that it displays text in the spectrogram : http://www.ebcon.com/WA0UWH/grabber/Argo/Gallery/Pub/20090223/010800.jpg . Interesting !

  5. dan says:

    >>This will be of tremendous use when the internet goes down during the inevitable zombie apocalypse.

    True, one of HAM radio’s stated purposes (in the usa) is to keep a small army of trained and equipped communications technicians available in case of emergency.
    The other stated purpose is to keep nerdy boy scouts out of trouble[1].

    [1] http://en.wikipedia.org/wiki/David_Hahn

  6. Kelly Martin says:

    @vic: That particular signal was sent by K6HX, who journals at least some of his ham radio exploits at http://brainwagon.org. If you ask him about it, I imagine he’ll be glad to explain that particular modulation in more detail. I’m not sure what the mode used to encode the visible text is called, but the stuff immediately above it on the spectrogram looks to me very much like WSPR, which is a mode I know Mark works in.

    Low-bandwidth low-power communication is of signficant interest to a lot of people, and not just for getting out advance notice of the impending zombie invasion, although it is certainly good for that too.

    For more on WSPR, see http://wsprnet.org/drupal/

  7. Kelly Martin says:

    Addendum to my last post: the modulation used to send the text is called MT-Hell and is described here: http://www.qsl.net/zl1bpu/FUZZY/MT_intro.htm

  8. Sam says:

    This is probably useful for communication over long distances, like between Earth and a space probe. The quality of the communication becomes more important than the bandwidth because it takes a long time for the signal to go to and from Earth to a probe anyway.

    Just my guess on applicability…

  9. @kelly martin: I’ve never heard it called mt-hell before, but as Hellschreiber.

    As for the usefulness, it’s simply an application of the concept of increasing power density by using a narrower bandwidth. These QRSS guys are getting mind blowing ranges (we’re talking >1,000 miles per watt range), though with luck almost any low power amateur station can do the same.

  10. As for applicability, first one that comes to mind is the VLF stations used to contact submerged submarines. High power in narrow bandwidth allows them to (slowly) send the subs callsign to signal them to surface to use VHF uplinks for actual communication.

  11. yoss says:

    Where can I find more information about building a receiver and transmitter? This seems pretty interesting.

  12. chippy says:

    Nice! good article.

  13. dan says:

    Here’s the info on how to build the transmitter,

    http://www.arrl.org/qex/2007/09/campanella.pdf

    but you might look into getting a ham license first (relatively easy)

    http://www.arrl.org/FandES/ead/classes.html

    Also, somewhere on the net you can find all the possible questions and answers to the test published by the FCC.

  14. Kelly Martin says:

    @yoss: search google for “QRP transmitter”; you’ll find lots of designs for various transmitters. QRP is an old signal code meaning “low power” (which in the ham world means anything under 5 watts).

    One particular kit that I’ve heard a lot about is the softrock, although I understand that they can be a lot of effort to get working. http://www.softrockradio.org/

  15. Kelly Martin says:

    btw, regarding licensing, the question pools in the US aren’t written by or published by the fcc. they’re developed and published by the national committee of volunteer examiners, or NCVEC; see http://ncvec.org

    i’ve put together mnemosyne decks for all three question pools (technician, general, and extra); see my blog for more information. http://nonbovine-ruminations.blogspot.com/2009/01/mnemosyne-study-decks-for-fcc-amateur.html

    the techniques being discussed in this article pretty much require (in the US) at least a general license; technicians have extremely limited access to HF (frequencies below 30 MHz capable of worldwide propagation). for those in countries other than the US, consult your national telecommunication ministry or amateur radio society.

  16. David says:

    @Kelly, you said…

    “One particular kit that I’ve heard a lot about is the softrock, although I understand that they can be a lot of effort to get working. http://www.softrockradio.org/

    I’ve built half a dozen variants of the Softrock radios. The smallest single band receivers take a few hours to build. I’ve never had one fail to work as expected. The most complex transceivers may take a day or two to build and configure with your software defined radio software.

    If you run into trouble there is a very active Yahoo Group for the softrock radios at:

    http://groups.yahoo.com/group/softrock40/

    See this page for a very detailed tutorial with photos on building one of the transceiver softrock versions:

    http://golddredgervideo.com/kc0wox/softrock/index.htm

    Regards, David

  17. qdos says:

    I have been into radio for a good long time I have a few hf radios and quite often have a listen to mid Atlantic aircraft, shipping etc…

    There is an underground network of radio operators called free banders who use frequencies they call ‘echo charlie’ who operate mainly on 6670khz LSB.

    I often thought it would be great to create some calling channels across the frequency spectrum from HF to UHF for free banders.

    It don’t seem right that one person or organization can own the a part of the electromagnetic spectrum, its like someone owning the clouds.

  18. Alex says:

    My first thought was – since this is a low bandwidth trade for reliability – what could be sent nowadays to make it useful. Then it occurred to me:

    Twitter!

  19. dan says:

    >>It don’t seem right that one person or organization can own the a part of the electromagnetic spectrum, its like someone owning the clouds.

    The EM spectrum isn’t the Internet. If you don’t want to listen to someone on the Internet, you just don’t listen to them. You block them. You route around them. The EM spectrum doesn’t really work that way. If you want it to work reliably, you have to agree on how it should be used.
    An extreme example would be operating a high-power broadband transmitter in the 100MHz region. No one around would be able to listen to FM radio. They can’t just not listen, it’s *there* and there’s no alternative.
    Another reason to get licensed is that it’s *so* incredibly easy, that the drag of getting fined (or getting beat up by your neighbors) is just not worth it.
    Also, no one has found a reason to fight over the clouds yet. Just give ‘em time.

  20. Oren Beck says:

    We need to have these projects coordinate with the “Whitespace” radio standards teams to prevent a tragic decimation of utility. These sub-QRP projects seem doomed to fall below “Listen before Transmit” protocols ability to detect. Decades ago I saw a demo of 150-190 Kc gear with ERP of <1 w communicate from Chicago to Detroit in loopback mode. Heavily amplified receive antennas and DEEP notch preselectors were part of the set up The details were a bit sketchy as explained by the presenter. But to my memory- it worked by having a transmitter at one end of that segment repeated by one at the opposite band end. Keying rate was not even considered as this was a way pre DSP project unless you call a 567 PLL a DSP device. Imagine making a repeater chain of devices operating in unlicensed modes by cross banding. Respecting of course the no RF modification rules. Just acoustic audio coupling with solenoids to press transmit buttons… With the amusing replication of QRSS like data rates by the accumulated delays.

  21. fartface says:

    @joe57005 That’s great. too bad all us Ham Radio operators have done this stuff at even higher data rates for decades.

    the Point is that he’s pulling a signal out of the noise floor very effectively. but when the Poop hit’s the fan, ham radio saves the day. not the govt, or police. Katrina Hams had a stable and working comms net for weeks before the police and feds pulled their heads out of the sand. It’s been that way for decades and will continue to be that way for at least another 300 years.

  22. colecoman1982 says:

    @qdos: It’s not a matter of someone “owning” part of the spectrum in the traditional sense, though major broadcast corporations like to talk about it that way, it’s about controlling access to a limited resource so that it remains useful to _anyone_. There are only so much bandwidth available. If there was no regulation, radio transition of information would be impossible because everyone would be fighting to “yell louder” than everyone else in order to be heard. We already see this in some bands such as Wi-Fi and cordless phones when used in densely urban environments. This is most important when it comes to emergency bands that can mean life or death if they become unusable.

  23. As for kits to build your own radio, I have heard nothing but good things about the rockmite kit.

    http://www.smallwonderlabs.com/Rockmite.htm

    But like all of them, notice that you’re going to need an amateur radio license. The first level would be enough to get on 7MHz and 3.5MHz Morse code only, and it is really easy to get (35 multiple choice questions, highest theory is along ohm’s law)

  24. Mardhanaya says:

    I love your blog. I am trying to get into modelling, do you have any good tips for me?

  25. Mastablubba says:

    Hellow yo

    just found this wanton prat Shaking Video on youtube…

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  26. Kriss says:
  27. Bud Plourd says:

    I just wanted to call out how great your writing skills are ;-)

  28. interested says:

    Hi. I need some advice . I want to know if there is software avileble to use with a hf radio that can send a digital signal wich is private between two stations? Like using bpsk or similar signal but with a pasword or something. Thanks for advice. It is for experemental use. Thanks

  29. interested says:

    Hi. I need some advice . I want to know if there is software avileble to use with a hf radio that can send a digital signal wich is private between two stations? Like using bpsk or similar signal but with a pasword or something. Thanks for advice. It is for experemental use. Thanks

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