Hacker News Reader

Comment by robotastic | Hacker News Reader

If you are interested in trying to listen your local radio system, try out Trunk Recorder: https://github.com/robotastic/trunk-recorder It works with the cheap $20 RTL-SDR dongles.

View on HN

Cool. Can I use a raspberry pi & one of those RTL-SDRs to replace the functionality of a typical hardware police scanner? Has anyone created images with all the software set up or is it easy-ish to get it set up. I have unix experience.

Aha! Now that I look at github, it's all pretty clear. Great work!

It would probably work pretty good for that. If you were just trying to listen to one talkgroup at a time, the raspberry pi should have enough CPU. Let me know how it goes! I happy to help patch things up to get this working.

OK. I'll get in touch via email. Thanks for the offer!

Cool! I last played with it a couple of years ago. Will have to mess with it again. Great work!

Do you know if the newer versions of RPi or other small boards have enough power to run this (i.e. dedicated RX feed nodes sort of like the ADSB RX nodes)? I know DSD is pretty processor intensive.

Thanks! So I have been playing with it on a RPi3. There are instructions here on how to build for the RPi: https://blog.hypriot.com/post/building-a-64bit-docker-os-for...

It has about enough CPU to handle recording about 2 streams at the same time. I think part of the problem is that Raspbian does not have the GCC flags optimized for the processor in the RPi3 and doesn't have 64bit enabled. I played a little with this image: https://blog.hypriot.com/post/building-a-64bit-docker-os-for... and it seemed to help a bit, but I didn't see huge gains.

People are using it with the ODroid, and I think they are able to do about 4 simultaneous recordings at the same time.

Are you using polyphase channelizer now, as opposed to individual XFIR tuners? If so, does that still provide better performance given sparsely occupied channels?

Unfortunately, I wasn't able to find a nice generic way to make it easy to configure the PFBs. There is a good thread on it here, with some sample code: https://github.com/robotastic/trunk-recorder/issues/76 If I can get a block of free time I am going to try and take another tilt at it.

I did switch to FFT based filters and that helped a lot. CPU requirements are a lot less. Using RTLs with 2M sample size, instead of SDR more bandwidth also helps. It is a poor mans version of HW-based channelization.

There is also this Rust based P25 decoder that I have been wanting to give a try: https://github.com/kchmck/p25rx It is a ground up re-write that doesn't need Gnuradio, so it could be pretty efficient.

I've used Raspberry Pis for this, but they tended to be bulky and overkill - the "Banana Pi Zero" is what I've been using lately. Combined with a PoE splitter (some have micro-usb, you can plug directly into the board), this works great - no more coax losses!

I use one for SDR playing, and one for receiving OTA ATSC and streaming to Kodi. I suppose I could have also installed a USB hub and run them both (or more) from one board.

Banana Pi Zero? What board is that? (I've been experimenting with various board for a project, so genuinely interested if this isn't a typo)

http://www.banana-pi.org/product.html

Thanks - but which one is the zero?

I'm sorry, it's an "Orange Pi Zero"[1] that I'm using, not a "Banana Pi Zero". I've gone through so many of these dev boards that it's hard to keep them all straight!

[1] http://www.orangepi.org/orangepizero/

Ah ha, thanks - I actually own two of those! They are awesome little boards, except for the wifi which is borderline unusable.

Would love to know more about OTA ATSC on Raspberry/Banana Pi -- everything I read tends to say that these ARM-based boards are good for playback only.

I'm using a K-World ATSC Tuner[1] on an Orange Pi Zero[2] (not Banana Pi as previously mentioned). Armbian[3] nightly installs with no modifications, and then Mythbackend[4] is installed using apt-get.

I bound to the machine's IP instead of localhost, and then was able to enter that into Kodi, where a list of TV stations Myth found appeared. It was surprisingly easy! I haven't had any issues with stuttering or skipping when streaming to a single Kodi instance - haven't tried any more than that.

[1] https://www.linuxtv.org/wiki/index.php/KWorld_ATSC_340U

[2] http://www.orangepi.org/orangepizero/

[3] https://www.armbian.com/orange-pi-zero/

[4] https://www.mythtv.org/wiki/Mythbackend

You have any specific RTL-SDR dongles to recommend for beginners?

Anything with a TXCO is pretty good.

I like these: http://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/ And these: https://www.amazon.com/NooElec-NESDR-SMArt-Enclosure-R820T2-...

Thanks a lot for the recommendation! I got the NooElec NESDR SMArt and it's working perfectly! Now to build my own antenna.

Reply on news.ycombinator.com