Software-defined radio

[DojoMojoMofo]

So, I'm not sure how familiar you guys are with this, but there are relatively cheap USB HDTV (TV in Europe anyway) receiver dongles available online, and many of them can be used as general-purpose software-defined radio receivers. This allows a PC user to receive everything from FM radio and police radio, to certain car remote fobs, NOAA weather satellite images, location and route data from passing planes, and so on, from about 24 MHz to 1850 MHz, depending on the tuner chip in the device.

I went on DealExtreme and ordered one with a RTL2832U (the basic, common radio chip that can be opened up like this) and an R820T tuner chip (newish chip with better range and less blank area than the older E4000 chip, which was the benchmark before.) I'm looking forward to getting it, though DX sometimes lists things that aren't in stock and takes forever to get them in, so my fingers are crossed for a quick delivery! I'll let you guys know what I find when I get it up and running.

In preparation, I'm building an interesting omnidirectional antenna with an optimal frequency range very well suited to these things. Here are some links!

Getting started:

http://www.rtlsdr.com/
http://www.reddit.com/r/RTLSDR/
http://en.wikipedia.org/wiki/MCX_connector

The omni antenna design: http://www.instructables.com/id/Fractal-Magic-DIY-HDTV-Antenna/?ALLSTEPS

Tuner shootout: http://www.hamradioscience.com/rtl2832u-r820t-vs-rtl2832u-e4000/

Some stuff to try:

https://sites.google.com/site/policescannerhowto/

http://www.rtlsdr.com/2013/07/how-to-receive-noaa-satellite-images/

http://www.rtlsdr.com/2013/07/needsec-decoding-flex-pager-traffic/

[DojoMojoMofo]

Here is the trick with the planes
http://hackaday.com/2012/04/16/playing-air-traffic-controller-with-software-defined-radio/

[Bryce McIntosh]

Nice, I've seen that stuff but never played with it.  Another one to look at is the HackRF which goes from 30MHZ to 6GHz, its a bit more expensive though ($275) and only does half duplex.

On Mon, Aug 5, 2013 at 4:14 PM, DojoMojoMofo <dojomo...@gmail.com> wrote:

Here is the trick with the planes
http://hackaday.com/2012/04/16/playing-air-traffic-controller-with-software-defined-radio/

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[Vincent Wolfe]

I've done quite a bit of reading on this, and have found a few of the SDR that can transmit as well.  Then with very clever development you could cause a lot of trouble :)  Anyways here is an interesting project by the guy who brought us the ubertooth one

http://www.kickstarter.com/projects/mossmann/hackrf-an-open-source-sdr-platform

I had a chance to meet him a few years ago, kinda pompous, but very intelligent.

I personally want to see more tablets with built in SDRs like http://www.meetearl.com/

Hey Matt how much did you end up paying for the equipment?

[DojoMojoMofo]

I got a couple for $13.60 USD each, and while I was at it, I grabbed a pack of 5 right-angle male gold-plated MCX connectors to run to the antenna I built, for $5.40 USD. Shipping was free... just a bit iffy. It's still not here yet, but apparently it was dispatched to Canada on the 19th.

[DojoMojoMofo]

So I've had the hardware for a few weeks now and I've got a good grip on how to use it...

It's pretty neat stuff! One thing that surprised me when listening to FM radio stations is that I can crank up the RF gain manually and greatly improve reception, using the cheap little bundled whip antenna to pull in CBC Radio 1 and 2 as clear as a local station! The tuner software I use for Windows, SDRSharp, is also pretty slick. I can record WAV files of the received signal itself - which can include a finite range of radio stations in a local frequency range - and then play it back in the tuner and tune into different stations in the recording! Another interesting thing is that while it may all be on chips and not vacuum tubes, the frequency definitely drifts a bit as it warms up. You can calibrate the receiver to match up to its indicated frequency, but it will take at least 10-15 min to get a really precise, stable tune when you first start up.

In addition to SDRSharp for receiving, I also use VB-CABLE, a Windows driver that lets me pipe sound straight from one application to another. This is key for decoding digital signals. Input and output ends are both set to 48 KHz sampling for best fidelity. Building on these 2 apps, I use Unitrunker for reading digital trunking (radio control) channels to follow multiple frequencies used by the same group. There's also PDW, a Windows pager decoder, and DSD - "digital speech decoder" - which... I actually haven't found any use for yet as no one around here seems to use digital walkie talkies.

If anyone's interested in specific frequencies, I'd be happy to share, but for now off the top of my head, I've found I can pick up:

• FM Radio (AM is too low frequency... though there IS a hardware mod to bypass the tuner chip and solder an antenna onto the receiver chip to do it...)
• Weather radio for Red Deer and area. Weak, narrow bandwidth signal, so it's nice for checking my calibration.
• FRS/GMRS radio. These are the cheap little walkie talkies sold in non-specialty stores. Signals are extremely weak though so it's tough. I made a half-wave dipole antenna for this, but it's still sketchy.
• Police radio. 3 frequencies mainly. I can't find a control channel for this, so I use a radio scanner plugin for SDRsharp to jump around to where it sees activity.
• The AFRRCS system? This includes fire trucks, ambulances, and possibly sometimes buses and police? This is hundreds of MHz higher, and uses a digital control channel in a format made by Motorola. Not hard to follow with Unitrunker and two receivers - one muted, watching the control channel, and one jumping around and following the voice conversations. It's kind of possible to do this with one receiver, but then you will not get any updated info about the network while listening to a voice, and when there is no voice, you'll get a harsh noise sort of like a recording of a big diesel engine, played a 2x speed, which is the trunking channel. While it seems possible, I have not yet mapped out the different groups using it to differentiate them, so it's a bit of a party line. I mainly hear first responders going on calls with it.
• GSM phone signals. I can't do a thing with these, but I can see them. Apparently it's pretty much cracked now. I haven't looked into it much.
• Alphanumeric pagers! There are 4 channels I can receive, some really low-tech and slow, some newer and faster. Pagers aren't dead... They seem to still enjoy use from hospitals, taxis, couriers, and server administrators, among a few others.
• Once I picked up some kind of construction site chatter for a half day on a non-public frequency.
• In theory, it should also pick up things like baby monitors, cordless phones, ADS-B transponders from passing planes (there are some neat programs for this that map them in realtime!), and CB and amateur radio conversations. I haven't seen anything like this yet, and would probably have to build a more appropriate antenna.

...which brings me to the Fractal Magic TV antenna... I'm undecided on it. It's not dramatically better at anything, but it is a bit stronger for FM radio, and a bit clearer for pager signals than the default antenna. I did not make or build a balun to isolate the antenna from the feed line, so the cable is also acting as an antenna somewhat, which is not optimal. That said, it's only about 4' long, so it's not horribly wrong either. I usually do use it instead of the whip antenna. I'm looking at designs for "discone" antennas, which are omnidirectional, and pick up a wide frequency range, starting from the minimum you design them to. I'm also considering a Yagi antenna to pick up signals in a certain direction, but I don't have much use for one right now. Maybe for FRS radio, since it'd work on a specific frequency range and boost strongly in a certain direction.

Anyway... that's what I've found so far. It's pretty entertaining for such a cheap investment, and now I've been pulled into reading all sorts of stuff about how antennas work as I get up to speed on this!