Discussions Not Related To Free State Wyoming (FSW) > Radio and Communications

More adventures with software defined radio (SDR)

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Paul Bonneau:
I just started an elaborate post and then lost it! Grrr...  >:(

Oh well, here I go again.

I started with this topic:
https://www.fswforum.org/index.php?topic=16482.0

I dug into it some more. I had tried to install all this stuff on my regular (Lubuntu) PC but it was a gigantic thing that didn't work well anyway (after I upgraded the software it stopped working). Anyway I uninstalled all that stuff and just dropped it for a while.

Then I got the bright idea of making a bootable flash drive and dedicating it to SDR. That way I won't have to mess up my normal system with all this experimental stuff. Fortunately there is a recipe out there to do just that:
http://sdrtrainingonline.com/free/
His stuff is paid training but the first 3 lessons are free, and the 2nd is the one that explains how to set it up.

The first part, installing linux on a flash drive, turned out to be the hardest because of a bug in the Ubuntu "Startup Disk Creator" tool.
https://help.ubuntu.com/community/Installation/FromUSBStick
I finally ended up going to Windows (my wife's computer) to create a linux flash drive! (lame...) The steps are to get on Windows, install something called "Linux Live USB Creator":
http://www.linuxliveusb.com/en/download
Then download the distro and use that tool to install it on a flash drive.

-- CONTINUED BELOW --

Paul Bonneau:
The guy in lesson 2 installed Ubuntu. I installed Lubuntu because it is smaller and easier on the cpu. This is important because SDR can be very compute-intensive (you might not be happy running it on a slow machine). It also saved me the steps he had to do to get rid of "Unity" in Ubuntu.
http://distrowatch.com/table.php?distribution=lubuntu
I did not run into the problem he had, where the driver needed to be blacklisted, as lubuntu 15.10 apparently already has it blacklisted. I did run into another problem, that gqrx did not start because "pulseaudio" was missing (it's probably already in Ubuntu but not Lubuntu). I pasted the error message I got into startpage and searched to figure that out (standard debug practice). All I had to do to fix it was to "sudo apt-get install pulseaudio".

Anyway, when you are done your bootable flash drive will have gnuradio (and its gui, gnuradio-companion) that allows you to actually design a radio. Many of the apps on this page were built with it:
http://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/
Those apps also give an idea all the different things you can do with SDR.

The actual interactive radio on linux is gqrx, which you can use to listen to FM stations (maybe more stuff - that's all I've done so far). The corresponding app on Windows is called sdr#.

The device I got is this one, a repurposed TV tuner:
http://www.amazon.com/NooElec-NESDR-Mini-RTL2832-Antenna/dp/B00P2UOU72
A better version is this, due to improved cooling:
http://www.amazon.com/dp/B0129EBDS2?psc=1
It is of course receive-only, but more powerful (and expensive) transmit and receive dongles like this one are available:
http://greatscottgadgets.com/hackrf/
It's best to get your feet wet with the cheapie.

There are tutorials out there to actually design radios with the gnuradio tool:
https://gnuradio.org/redmine/projects/gnuradio/wiki/Tutorials
http://greatscottgadgets.com/sdr/
This stuff is fascinating. Become a signal-processing guru!  :)

With these cheap dongles, you need some extra hardware to get into the ham bands, e.g.:
http://www.amazon.com/dp/B009LQT3G6?psc=1
Possibly not needed with the more expensive dongles, as they have broader frequency range.

In my earlier investigation I wondered about calibrating this cheapie dongle. This page has a semi-understandable procedure:
https://www.jeroennijhof.nl/wiki/index.php?title=Software-Defined_Radio_on_Ubuntu#Listening_for_a_Payload
I never did see the twin peaks as he talks about, but a single peak that I put in the middle of the audio spectrum. I ended up with a -1.575kHz offset, a lot smaller than his (I suspect I have better hardware). Or, it's possible there was nothing!

Paul Bonneau:
Ah, now I see with that last link he is talking about calibration when listening to weather baloons, heh...

An added advantage of doing this on its own flash drive is that if the computer I am using does not have the horsepower to run the signal processing, it's a simple matter to take the flash drive and use it to boot a more powerful computer.

Paul Bonneau:
Here is a very good description of the workings of gqrx. It helped me a lot!

http://gqrx.dk/doc/practical-tricks-and-tips

I used this to calibrate the dongle oscillator (mine needed 75ppm). I just tuned to an FM station that had the digital sidebands; these have very vertical sides and it is easy to use those sides to center the display with the ppm adjustment.

It also shows how to capture and display weather reports, just as one example of what you can do with SDR.

Right at the end there is a comment about the internal laptop microphone. As I suspected, this is disabled when a mic plug is plugged into the mic jack. This would be a good security measure, never mind the effect on your audio - just like putting some tape over the laptop cam.

SunDog:
I've done this on a couple of Windows machines. I've had no problems with the RTL dongle overheating, and my graying dual core PC (ca 2006) can keep up easily. I had one older XP laptop fail to run the SDR software due to a slow, single core CPU. With the help of a PC guru at the local electronics club, I am refitting a fast laptop with Fedora, and the SDR software is one goal. First I have to re-build the laptop - I bought it used, and the heat sink was plugged up with what I can only hope was closely shaved dog hair. Before the overhaul I had both Ubuntu and Fedora running, but the overheating was driving me crazy, and I want to take the 32 GB SSD out (leaving the 500 GB hd in) since neither flavor of linux seemed to know what to do with the SSd.

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