Welcome to the World of Software Defined Radio (2016)
robertputt.co.uk
robertputt.co.uk
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.
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 cannot find the discussion, but the info is here: http://www.rtl-sdr.com/tag/rpitx/
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
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.
https://github.com/theori-io/nrsc5
And a transmitter for GNU Radio.
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)
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.
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.
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!
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.
Is it something that is only likely to happen with older and less isolated microwaves?
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.
Customers might value using bluetooth and wifi. Not all pressures are regulatory!
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.
availability of cheap hardware and wife software selectionIt'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).
"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...
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.
Should be written using the proper SI prefix, MHz. There's a huge difference between the milli (m) prefix and mega (M).
Listen to Radio from around the globe
http://radio.garden/live/ (drag the map to tune in)
Having received my ticket recently, I'd love to try some digital ham radio modes without spending a fortune.
Edit: "ticket" = license?