DVB-T type devices such as the one referred to in this article are indeed remarkably flexible but keep in mind that they are only able to receive. In my case, that quite rapidly exhausted my curiosity.
I'm now eagerly awaiting delivery of a LimeSDR (https://www.crowdsupply.com/lime-micro/limesdr), one of several hacker-friendly radio peripherals that can both receive and send (in the LimeSDR's case, in full duplex mode) because of course having a transceiver is a whole different ball-game. GnuRadio can serve as the logic of both receivers and transmitters.
Of course depending on country, frequency and transmitted power you may require licences to operate.
Sending capability (at least here) requires amateur radio license. It is technically illegal to even own transmit capable equipment without a license and you can operate it only under supervision of licensed person.
This is not at all true in the US: it is not "technically illegal" to own transmit-capable equipment without a license.
It is true that transmissions are regulated by law in every country, and the particular license you need will be determined by frequency band and power. In the US, there are some cases ("Part 15") where no license is required.
as noted above "part 15" rules actually allow low-power transmission along a multitude of bands. In some bands you are restricted to only a few mw of power, others like the scientific bands allow more.
That cannot literally be true... your cellphones and wifi devices are radio transmitters and I'm assuming owning either is not specifically illegal. I assume you mean unlicensed equipment?
You are intentionally misinterpreting what I said, or maybe you do not know that some bands can be used by commercial devices. That doesn't mean you can do whatever you wish on any bandwidth you want.
But even in something as common as WiFi you still have regulations, like channel 14, which as far as I know only works in Japan by default. Other common restriction is transmitting power.
I’m not ”intentionally misrepresenting”, nor did I misunderstand — I was just being comically pedantic, because the absolute terms you couched your statement in are obviously not true, because a lot of personally-owned devices transmit radio and that doesn’t get you into any trouble whatsoever.
Yeah, I get that feeling too, but the problem is the licensing and stuff... The good news is I get my send and receive fix from LoRa and The Things Network, still has legislation you must abide by like duty cycle and power limits, but doesn't have the headache fo being a HAM.
What is such a headache about amateur radio? The test is less expensive than two cups of coffee in most places and the license itself is free. I'd wager if you're a regular here, you'd have no problem learning the theory and rules to pass the test, especially if you're genuinely interested in radio communications.
Is it still a requirement to be fluent in morse code? If so I personally feel this requirement is redundant in the current age with the tooling we have available which can easily encode and decode morse on our behalf... If not maybe I'll consider it, until then I would prefer to dedicate my time to learning something more current / relevant than memorising morse.
In the US morse hasn't been a requirement in the last decade or so (and I think basic classes without it even longer), and many other countries have dropped it as well.
I got my "no-code Technician" class license in 1998, not long after they did away with the code requirement for Technician. At that time, Novice, General, Advanced, and Extra classes all still existed and all required Morse code. Later the FCC dropped Novice and Advanced and later still removed Morse code from all tests.
Still, I wish I had started with Novice so I'd have learned Morse early on.
I'm in Italy. Morse has not been a requirement since 2005 or so, if memory serves correctly. If I'm not mistaken it has been phased out as a requirement throughout the EU as part of the communications legislation harmonisation process.
It's not a requirement in Germany either (or anywhere, really). Our local HAM radio club spends most of its time with modern technologies nowadays like 5 Ghz high-bandwidth radio links nowadays.
In the US there is no morse any more. The technician license test is very easy and will give you all the VHF/UHF bands and a few narrow HF bands. General class test is a bit harder and requires some basic math and electronics knowledge and will add most of the rest of the frequencies. Extra is quite difficult (for me at least) and gives you everything else. Each test is usually about $15.
You can also keep progressing in the tests under the same $15 fee. That is, after taking and passing the tech test, you can take the general during the same session (same day) without having to pay another $15.
I did it this way for the Tech/General/Extra, hammered all three of them out in the same session spending only $15 that Saturday morning.
I did it this way for the Tech/General/Extra, hammered all three of them out in the same session spending only $15 that Saturday morning.
Guess which one of us has the EE degree. :-) Kudos, that’s hardcore doing it all in one swipe. General took a little study for me, and after practically memorizing the questions, easily passed it. But Extra, damn, I’m going to have to bone up on some electronics before I pass that one. Or just do without the little sliver of frequency it gains me.
It's funny, I spent a month studying for general, and then three days studying for extra. Barely passed the general exam and easily passed the extra. (I took my tech exam almost precisely one year earlier)
>In my case, that quite rapidly exhausted my curiosity.
I've been exploring the world of radio emissions with rtlsdr since 2013 (http://superkuh.com/rtlsdr.html) and I'm still finding plenty of new things to do.
IMO, the newest cool stuff with rtlsdr are computational hacks to align multiple non-coherent receivers in time to do distributed direction finding and the like.
I recently read here that a Raspberry Pi can be turned into an SDR transmitter by attaching a wire to a pin. On paper, the specs look impressive (for a $20-$30 device), but I would love to know the RF quality of the resulting waveform.
On noise, this is what I suspect, too; thus I am not trading in a couple of HackRF One-s that I am currently playing with. Still would be useful to know the numbers.
On the range, I did not pay much attention (but maybe I should have): the power of HackRF one is low, too; one needs an amplifier to transmit in the open air anyway. Do you think that the rpitx TX power is not suitable for table-top sized prototypes?
You will need a antenna that is resonant on the frequency you're transmitting on for any hope of the signal leaving the immediate proximity of the Pi. It would also be a very good idea to filter the signal coming out of the Pi to reduce the strength of any frequency spurs accompanying your Pi generated signal and to keep your transmission legal.
Yeah I have a low pass filter from QRP Labs ($8?) and an MFJ tuner as well as a very long wire. If I precisely measure the wire I could skip the tuner.
The one time I tried it without any filter or anything and viewed the signal on my RTL-SDR the quality was horrible. Spurs and distortion and strong harmonics.
What exhausted mine is the fact broadcast digital FM radio in the US is protected by patent and license encumbered encoding schemes, so there are no open-source decoders for GNU Radio and derivatives.
Interesting! A conspiracy theory of mine is that one factor in the push to digital TV and radio was to prevent widespread pirate transmissions, as much more people got access to "studio" equipment aka multimedia devices. Of course if that was one motivation it is moot now, since the internet has become more relevant than traditional media.
Still, this might be cool for subversive actions in countries with censored media, in an "Arab spring" like situation. Just a laptop, SDR and antenna on a driving truck and your on air (ofc I think there is not much overlap in places with widespread digital radio and places where you'd need to do this anyway)
SDR has completely changed the landscape. I'm the developer for the digital television component of GNU Radio. There are transmitters for ATSC, DVB-T, DVB-T2, DVB-S, DVB-S2 and cable QAM. Here's a video of DVB-S2 being transmitted with a LimeSDR.
That micro limesdr looks very tempting. Also someone on /r/rtlsdr mentioned PlutoSDR which is also in a similar price range. I need to start to save up!
Lime has the best hardware/specs at their price points, but their software toolchain is atrocious; just trying to do simple tasks in GNURadio is so flaky/error prone. I wish I'd gone with ahackrf (michael ossmann products) rather than the lime.
I've met Mike a couple of times, and he's a great guy, a great teacher, and super passionate about open source. The HackRF is a revolutionary little board, but it seems to be getting a little outdated compared these newer projects. I'm hoping he'll have something new soon!
Right, HackRF is not going to cut it if your building a cell phone repeater. But for home/hobby projects it's pretty good. I own a LimeSDR. It's not just the hardware, you also have have good software drivers. Everything open source in RF pretty much uses GNUradio, and there are endless problems trying to get LimeSDR working with GNUradio. Just read the message boards for LimeSDR. The first thing lime tells you do so is install Pothos which has zero support in open source community, so good luck. I wish it were otherwise as I said I've spent a lot of time fiddling with my limesdr
I got a Lime and I've not really had a great experience with it. You can't actually receieve HF with it unless you desolder an inductor. Also mine has a HUGE DC bias which introduces a ton of noise and basically cuts the usable bandwidth in half, if not more. Sadly I think these things were overhyped and/or ran into design issues that keep them from living up to the promise
This is very upsetting, I have been really looking forward to getting my LimeSDR. I’ve already opted for having it delivered with the offending inductor removed, but reading of high DC biases and (elsewhere in the thread) bad drivers and poor interoperability with GnuRadio has kind of spoiled my excitement.
SDR and RF in general has always felt like black magic for me, but the availability of cheap hardware and wife software selection makes this accessible to everyone. For newcomers I recommend the RTL-SDR subreddit, plenty of great resources. My latest venture is a jam and replay attack on keyless entry systems eg vehicles, project page is here: https://github.com/trishmapow/CC1101-FSK
Not gonna lie. As a radio guy, our terminology is messed up. My favorite though is using superlatives.
Low Frequency (LF), Medium Frequency (MF), High Frequency (HF).
You'd think that maybe HF is WiFi, but you gotta remember these terms were invented back in the early days of radio. HF is between 3 and 30 MHz.
You have Very High Frequency and Ultra High Frequency, but that only takes us to 3 GHz. 5 GHz Wifi is technically SHF -- or Silly High Frequency.
But we also refer to these frequency bands in terms of MHz, or if we feel like it, wavelengths. Since radio signals travel (effectively) at the speed of light (m/s), we can multiply Hz (1/s) by a distance and get wavelength. (c = f * l). 144 MHz then is the 2 meter band, or VHF as we call it.
Confused yet? Wait until we start talking about baseband and I/Q signals!
> 5 GHz Wifi is technically SHF -- or Silly High Frequency
For those curious, op's right and it actually is SHF, but it stands for Super High Frequency. I don't understand humour, only RF (and even that, barely).
Here's a fun semi-relevant science experiment you can do at home: running a microwave will kill nearby wifi and bluetooth connections. Isn't that strange?
Try it with a par of bluetooth headphones right now!
Most people aren't using wifi near running microwaves, so it's hard to notice. Some microwaves leak more than others, but none of them are required by the fcc not to interfere with 2.4ghz wifi. The FCC says that they can actually leak an unlimited amount of radiation at that frequency [1], although obviously if it's high enough to start cooking people standing nearby other agencies than that the will get involved.
I bet ya an upvote that yours still leaks enough. One thing to try is to put your phone next to the microwave and place your bluetooth headphones or speaker riight at the limit of its range. Turn on the microwave and see what happens!
I once worked at a site that had the Wi-Fi access point for one side of the office in the break room. There was, of course, a microwave in the break room. There were frequently complaints around the lunch hour that the Wi-Fi didn't work well, though strangely it worked earlier and later in the day.
My parents have an open layout house with the kitchen directly behind the living room. Because of this, it was always common to get up, walk and make some popcorn while watching a movie.
Once they started using netflix, this habit had to be broken quick.
I've found it varies a lot based on the microwave, distance (obviously) and positioning. My old apartment, anywhere in the kitchen and it'd kill my connection to my headphones. My new apartment (new appliances, too), I can be standing right in front of the microwave, and nothing.
Huh, my TV kept dropping the connection while streaming stuff from my computer downstairs. I wasn't using the microwave but maybe neighbors were... didn't consider this possibility. :D
No. It's basically defined relative to the audio spectrum.
Low begins at a point that is squarely out of the human hearing range: 30 kHz. That is just fast enough to start encoding intelligible speech into a carrier.
(Two decades that lie within audio range are called ultra-low and very-low.)
On the opposite end, the ITU acronyms now extend up to the 30-300 GHz decade, which is termed EHF.
No, it is definitely not relative to audio. Sound waves and radio waves are of completely different carriers.
The reference medium frequency band in electromagnetic (EM) is based on the original AM broadcast frequency ranges (first time broadcasts could be separated into distinct frequency bands). Medium frequency (MF) is just what we started with broadcasts and the ranges expanded around that.
Audio and Radio frequency ranges are completely unrelated.
Radio is electromagnetic and audio is air pressure. As far as human hearing is concerned there is only one "band" 20 Hz to 20kHz with greatest sensitivity from 1kHz to 4kHz. That is air pressure wave propagation and has nothing to do with radio frequencies and propagation of electromagnetic waves in the ULF to VLF ranges.
> Sound waves and radio waves are of completely different carriers.
(ITYM "media"; a carrier is a waveform onto which a signal is imprinted.)
In an electronic circuit it's just frequency, whether the waveform came from a microphone, or from a radio-frequency oscillator.
When you mix audio into a carrier to produce a radio signal, it's all just math functions realized in the same medium: the medium of voltage/current changes versus time.
In radio, audio frequencies that were once carried through the air are imprinted, via electronics, onto radio frequencies.
For instance, a 500 Hz audio tone modulating a 700 kHz AM carrier creates 700.5 kHz and 699.5 kHz side bands (chopped to just one side band with SSB (single side band) encoding). The fact that there had been a sound wave moving through the air is now imprinted in the radio wave medium.
"Low frequency" in radio basically starts in a range that is outside of radio, yet high enough to be usable for carrying audio signals.
There is a glaring error at the beginning of this article under the "things you cannot do with SDR."
"Listening in on the conversations of Ham operators."
In the US at least, there are many VHF/UHF Ham bands easily received by SDR. I use an Airspy on Mac OS X, and although the software is terrible, there is plenty to listen to.
I was thinking / wondering the same. Many new HAM operators get handheld radios that use the 144MHz (2 meter) and 440MHz (70 cm) bands. Both of these seem to be within range of this device. You can also build a dipole antenna for these frequencies for a few dollars. That would allow many of us to listen to repeaters in our local area. RepeaterBook.com (or the mobile app) is a good resource for listing repeaters near you.
I haven't had time to write much detail about this but here's an antenna I built recently. A quick google search will bring up dozens of other designs.
Maybe they were thinking HF (High Frequency), which is what's used for long distance/international contacts and what many people think when they think "ham radio". AFAIK the USB stick receivers can't receive HF. But that's a hardware limitation, not SDR limitation. There exist SDRs that can do HF, they just don't cost $15.
Actually the latest RTL-SDR has a software switch for direct sampling. Which isn't great quality, but with an indoor wire antenna in the basement (!) I received JT65 transmissions from 47 states in the course of a few evenings. Hawaii, Vermont, and Alaska are the ones I missed. However, I did hear Hawaii... On SSB!!
Not that I've seen. There exists SDR hardware for transmitting, but all seemed to start at multiple $100's. In any case note that you will almost certainly need a license to transmit on most interesting frequencies and power levels.
There is the LimeSDR Mini that is currently being croudfunded[1]. For $140 USD you would be hard pressed to find anything like it that would give you full duplex across that frequency range. I own the full size LimeSDR device and it has been a great piece of hardware for playing around with.
Lime has the best hardware/specs at their price points, but their software toolchain is atrocious; just trying to do simple tasks in GNURadio is so flaky/error prone
Basically, it is an SDR for multiple users and an online interface. It's RX only, of course. More options are available at websdr.org but the above is my favorite.
This is really wonderful, thank you for the link. I'm enjoying now a radio broadcast from..Malawi. The diversity of voices around the world, the ease of moving and focusing on stations - one of the best things I've seen on the web.
91 comments
[ 2.8 ms ] story [ 117 ms ] threadI'm now eagerly awaiting delivery of a LimeSDR (https://www.crowdsupply.com/lime-micro/limesdr), one of several hacker-friendly radio peripherals that can both receive and send (in the LimeSDR's case, in full duplex mode) because of course having a transceiver is a whole different ball-game. GnuRadio can serve as the logic of both receivers and transmitters.
Of course depending on country, frequency and transmitted power you may require licences to operate.
It is true that transmissions are regulated by law in every country, and the particular license you need will be determined by frequency band and power. In the US, there are some cases ("Part 15") where no license is required.
But even in something as common as WiFi you still have regulations, like channel 14, which as far as I know only works in Japan by default. Other common restriction is transmitting power.
Still, I wish I had started with Novice so I'd have learned Morse early on.
I did it this way for the Tech/General/Extra, hammered all three of them out in the same session spending only $15 that Saturday morning.
Guess which one of us has the EE degree. :-) Kudos, that’s hardcore doing it all in one swipe. General took a little study for me, and after practically memorizing the questions, easily passed it. But Extra, damn, I’m going to have to bone up on some electronics before I pass that one. Or just do without the little sliver of frequency it gains me.
I've been exploring the world of radio emissions with rtlsdr since 2013 (http://superkuh.com/rtlsdr.html) and I'm still finding plenty of new things to do.
IMO, the newest cool stuff with rtlsdr are computational hacks to align multiple non-coherent receivers in time to do distributed direction finding and the like.
See also, https://ptrkrysik.github.io/
I cannot find the discussion, but the info is here: http://www.rtl-sdr.com/tag/rpitx/
Technically it works, but it's very noisy and the transmission range isn't far enough for anything too serious.
A full duplex SDR would be a better investment.
On the range, I did not pay much attention (but maybe I should have): the power of HackRF one is low, too; one needs an amplifier to transmit in the open air anyway. Do you think that the rpitx TX power is not suitable for table-top sized prototypes?
It says a dynamic range of only 13 dB on the levels.
Any links to write-ups/HOWTO's would be tremendously appreciated!
This is a pretty good write up of using the Pi as a wspr transmitter: https://github.com/JamesP6000/WsprryPi
https://github.com/theori-io/nrsc5
And a transmitter for GNU Radio.
https://github.com/argilo/gr-nrsc5
Still, this might be cool for subversive actions in countries with censored media, in an "Arab spring" like situation. Just a laptop, SDR and antenna on a driving truck and your on air (ofc I think there is not much overlap in places with widespread digital radio and places where you'd need to do this anyway)
https://www.youtube.com/watch?v=Ed7iy0gVywo
It's been out for a while.
The newer option is LimeSDR, which just shipped: https://www.crowdsupply.com/lime-micro/limesdr
(Note that you need to comply with all local laws regarding transmitting).
Low Frequency (LF), Medium Frequency (MF), High Frequency (HF).
You'd think that maybe HF is WiFi, but you gotta remember these terms were invented back in the early days of radio. HF is between 3 and 30 MHz.
You have Very High Frequency and Ultra High Frequency, but that only takes us to 3 GHz. 5 GHz Wifi is technically SHF -- or Silly High Frequency.
But we also refer to these frequency bands in terms of MHz, or if we feel like it, wavelengths. Since radio signals travel (effectively) at the speed of light (m/s), we can multiply Hz (1/s) by a distance and get wavelength. (c = f * l). 144 MHz then is the 2 meter band, or VHF as we call it.
Confused yet? Wait until we start talking about baseband and I/Q signals!
For those curious, op's right and it actually is SHF, but it stands for Super High Frequency. I don't understand humour, only RF (and even that, barely).
https://en.wikipedia.org/wiki/Super_high_frequency
Here's a fun semi-relevant science experiment you can do at home: running a microwave will kill nearby wifi and bluetooth connections. Isn't that strange?
Try it with a par of bluetooth headphones right now!
Is it something that is only likely to happen with older and less isolated microwaves?
Customers might value using bluetooth and wifi. Not all pressures are regulatory!
I bet ya an upvote that yours still leaks enough. One thing to try is to put your phone next to the microwave and place your bluetooth headphones or speaker riight at the limit of its range. Turn on the microwave and see what happens!
[1] https://www.ecfr.gov/cgi-bin/text-idx?SID=c7be03a4f7b02514ce...
Once they started using netflix, this habit had to be broken quick.
I replaced all of my light bulbs for bluetooth light bulbs.
Fun thing is that I can't turn on the light when the next door neighbors use their microwave. And by fun I mean dealbreaking.
No. It's basically defined relative to the audio spectrum.
Low begins at a point that is squarely out of the human hearing range: 30 kHz. That is just fast enough to start encoding intelligible speech into a carrier.
(Two decades that lie within audio range are called ultra-low and very-low.)
On the opposite end, the ITU acronyms now extend up to the 30-300 GHz decade, which is termed EHF.
https://web.archive.org/web/20131031020427/http://www.itu.in...
The reference medium frequency band in electromagnetic (EM) is based on the original AM broadcast frequency ranges (first time broadcasts could be separated into distinct frequency bands). Medium frequency (MF) is just what we started with broadcasts and the ranges expanded around that.
Audio and Radio frequency ranges are completely unrelated.
Radio is electromagnetic and audio is air pressure. As far as human hearing is concerned there is only one "band" 20 Hz to 20kHz with greatest sensitivity from 1kHz to 4kHz. That is air pressure wave propagation and has nothing to do with radio frequencies and propagation of electromagnetic waves in the ULF to VLF ranges.
(ITYM "media"; a carrier is a waveform onto which a signal is imprinted.)
In an electronic circuit it's just frequency, whether the waveform came from a microphone, or from a radio-frequency oscillator.
When you mix audio into a carrier to produce a radio signal, it's all just math functions realized in the same medium: the medium of voltage/current changes versus time.
In radio, audio frequencies that were once carried through the air are imprinted, via electronics, onto radio frequencies.
For instance, a 500 Hz audio tone modulating a 700 kHz AM carrier creates 700.5 kHz and 699.5 kHz side bands (chopped to just one side band with SSB (single side band) encoding). The fact that there had been a sound wave moving through the air is now imprinted in the radio wave medium.
"Low frequency" in radio basically starts in a range that is outside of radio, yet high enough to be usable for carrying audio signals.
"Listening in on the conversations of Ham operators."
In the US at least, there are many VHF/UHF Ham bands easily received by SDR. I use an Airspy on Mac OS X, and although the software is terrible, there is plenty to listen to.
I haven't had time to write much detail about this but here's an antenna I built recently. A quick google search will bring up dozens of other designs.
https://www.joeldare.com/topics/amateur-radio/#gift-card-dip...
Should be written using the proper SI prefix, MHz. There's a huge difference between the milli (m) prefix and mega (M).
Having received my ticket recently, I'd love to try some digital ham radio modes without spending a fortune.
Edit: "ticket" = license?
1. https://www.crowdsupply.com/lime-micro/limesdr-mini
http://websdr.ewi.utwente.nl:8901/
Basically, it is an SDR for multiple users and an online interface. It's RX only, of course. More options are available at websdr.org but the above is my favorite.
Caution, it can be a huge time sink.
Listen to Radio from around the globe
http://radio.garden/live/ (drag the map to tune in)