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Comment by qubex | Hacker News Reader

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.

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>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.

That sounds really interesting, have you got a url?

https://www.rtl-sdr.com/tracking-wildlife-with-tdoa-directio...

See also, https://ptrkrysik.github.io/

Also, http://www.panoradio-sdr.de/tdoa-transmitter-localization-wi...

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.

I cannot find the discussion, but the info is here: http://www.rtl-sdr.com/tag/rpitx/

>but I would love to know the RF quality of the resulting waveform.

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 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?

There are some details here: http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll...

It says a dynamic range of only 13 dB on the levels.

As an Amateur Extra I've used a Pi to transmit WSPR 24/7 and was once heard in New Zealand from Ohio. No amplifiers even...

Just to triple-confirm, there was no additional hardware besides the Pi? I'm assuming at least some sort of antenna was involved...

Any links to write-ups/HOWTO's would be tremendously appreciated!

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.

This is a pretty good write up of using the Pi as a wspr transmitter: https://github.com/JamesP6000/WsprryPi

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.

It's been cracked. Here's a receiver for RTL-SDR.

https://github.com/theori-io/nrsc5

And a transmitter for GNU Radio.

https://github.com/argilo/gr-nrsc5

Thank you! I'm happy to be corrected. :-)

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.

https://www.youtube.com/watch?v=Ed7iy0gVywo

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

same experience, sadly.

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.

Well, I wish you the best. It's possible they're just having QC issues. Yours might be perfect!

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)

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's policies on free and open source software and hardware (https://www.crowdsupply.com/lime-micro/limesdr#free-and-open...) pushed me over the edge. The LimeSDR Mini project (https://www.crowdsupply.com/lime-micro/limesdr-mini) has my money.

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

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.

Yeah, GMRS band is actually pretty permissive as long as you stay under the power limit(5W?).

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.

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