Nano SDR

Nano size remote RTL-SDR computer with remote GUI and remote audio possibilities.

If you need a guide that just works, you are spot on !

My requirements:

  • Low power computer but powerful as well (for solar powered location)
  • Linux compatibilty
  • Noiseless solution (no moving parts in it - SSD and passive cooling)
  • Compatility with Linrad (hardware and software). After power loss it should boot back on (BIOS functionality)

I just tested this BIOS feature and it works perfectly, very important for remote operation. Of course, the Raspberry Pi boots back on, but normal computers dont do it, unless there is a BIOS feature. Nano has it.


My choice of hardware was Zotac:

Product Name ZBOX CI320 nano
Chipset Intel Celeron N2930 (quad-core, 1.83 GHz) Burst frequency up to 2.16 GHz
Memory Type DDR3L
Memory Speed 1333 MHz
Capacity up to 8GB
LAN 10/100/1000Mbps
WiFi 802.11ac + Bluetooth 4.0
Audio Analog Stereo output
Digital 8-ch via DVI-HDMI adapter, S/PDIF
Storage Hard Drive Support 2.5-inch SATA 3.0 Gb/s HDD/SSD
Memory Card Reader 3-in-1 (SD/SDHC/SDXC)
Ports
HDMI 1
DisplayPort 1
SATA 1 (SATA 3.0 Gb/s)
eSATA 1
USB Ports 4 USB 3.0 (back panel) 2 USB 2.0 (front)

The COOLEST feature is PASSIVE COOLING
Form Factor mini-PC nano version.

As far as I know it is the ONLY palm-sized computer with a powerful Intel Celeron quad-core processor and passive cooling and with such features on the world market.

For such a small size NanoSDR something really small and low power consumption but good quality screen is recommended.
My choice was: 7inch 1280*800 N070ICG-LD1 IPS LCD Display (from ebay these are cheap)
Of course the NanoSDR works perfectly without a screen as well. I just wanted to have some visual feedback.


For RTL-SDR in Linux, the best choice is the application Linrad.
However if you want to use remote audio then the choice of OS is a little bit reduced to one distro.

The developer of Linrad recommends to use Linrad with pulseaudio on Fedora 20 linux.
This is a distro that works well with Portaudio and Pulseaudio currently. (February 2015)

So, knowing this good advice, I started to install Linux Fedora 20 on the zotac nano.
All you need is a bootable USB stick with fedora 20.

Important to install the Fedora 20 LXDE : Download link
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/20/Live/x86_64/Fedora-Live-LXDE-x86_64-20-1.iso
Copy the iso onto your USB with this tool Universal USB Installer – Easy as 1 2 3 | USB Pen Drive Linux

The default gnome desktop takes so much CPU resources unnecessarily, we need the CPU for signal processing of SDR.
So the LXDE lighweight desktop is much better for this application.

Once the Fedora OS is up and running you need 5 application to be installed:
- PulseAudio Volume Control
- wine (latest)
- Teamviewer (latest)
- Skype (latest)
- Linrad (plus osmocom and portaudio)

As for Linrad there are many training videos from the developer http://www.sm5bsz.com/linuxdsp/videos.htm
but all you need is svn and install the latest version of Linrad. The link is here:
http://www.sm5bsz.com/linuxdsp/linroot.htm

svn checkout https://svn.code.sf.net/p/linrad/code/trunk linrad

Once you checked it out go into the linrad directory and run this:
./configure -- with-help

This will tell you what else you need to install. It is depending on your system but for RTL-SDR you will need the osmocom and portaudio at least.
You can possible use a couple of RTL-SDR dongles but what I use is this one: http://janielectronics.com

Basically after all installation you are ready, just configure the PulseAudio Volume Control as shown in my video.

http://youtu.be/_fsyxn8Lb_M

With PulseAudio Volume control you create a dummy/virtual audio device which is used to loop back the system audio / Linrad audio to Skype.
From Linrad side, Portaudio has the be installed and enabled and selected for use.

Startup steps:
1) connect to the remote nano-SDR via Teamviewer
2) start skype and call your local computer
3) start from menu PulseAudio Volume control on Nano SDR and select Input device as Monitor of Dummy Output
4) start Linrad, press U for settings and press B for audio settings, select Y for portaudio and select pulse device from the list.

That is all, now you can listen the local radio stations via NanoSDR over the internet from several 1000`s of miles away. Isn’t it cool?

Notes:
- advantage of using Teamviewer over x2go : Teamviewer creates its own VPN, no need port forwardings, Teamviewer uses around 400kbit/sec which is not much.
- advantage of skype over any alternatives: sound quality of skype is top of the class, no wonder Microsoft bought them out.
- if you use the RTL-SDR from http://janielectronics.com/ please be aware that these are HF and UHF band types with an push button to switch the band. After power up the NanoSDR, the default band is always UHF, so if you want to use the SDR for HF bands get a small clip and clip it on the push button in HF mode. This way it will always switch the RTL-SDR to HF band after connected to power.

I clip like this or smaller if you have: Crocodile clip

The following test is showing the needed internet speed for NanoSDR operation.
The test conditions:


NanoSDR: running Teamviewer and Skype, both are connected, running Linrad and listening a WFM broadcast radio station.

Receiver: normal Linux Mint computer, running Teamviewer and Skype and connected to NanoSDR

I listen the remote WFM radio station via Skype and the needed data speed is around 65kbit/sec which is super good. It should work even over 3G mobile network.
I noted if I do some settings over Teamviewer, the GUI transfer needs more data, but it never went above 550kbit/sec which is still well inside the 3G mobile HSUPA uplink speed.

I have done a CPU temperature monitoring test with the following conditions.:
- room temperature is 22 Celsius (72F) where the nanoSDR is located
- Linrad is running already for 45 minutes with Teamviewer and Skype connected

as shown the highest CPU core temperature is 134.6F (57 Celsius) which is perfectly normal


Besides Linrad you can also build on your own radio receiver with GNU Radio and the RTL-SDR dongle.
The good news is that GNU-Radio works very well with Fedora 20 and installation is super easy, only 2 commands:
yum install gnuradio
yum install gr-osmosdr
and start it with:
gnuradio-companion

Besides Linrad and GNU Radio applications there is a 3rd SDR application I recommend to try.
GQRX

it is very similar the SDR-Sharp but it runs on Linux and of course on Fedora 20 too.
Installation is just one command:
yum install gqrx
Very easy to configure and use and it has an AFSK decoder so you can decode the aprs traffic "out of the box" with it.

It needs about the same CPU resource as Linrad.