Hi friends, in this time of global pandemic, all are forced to be inside. To avoid the boredom of self exile some thing extra has to be done to dissipate stored energy. I adapted few of my hobbies to do the same. Today I want to share how and what I was doing during past few weeks.
2m Flower pot Antenna
For my VHF activity I made VK2ZOI design flowerpot antenna. The first one i made is a described here. This one worked exceptionally well it outperformed my existing (refurbished) 5/8 GP. i could reach 30 km with only 5 watts with 59 report from 2 stations and 57 from other stations. Earlier it was not possible to reach them from my QTH (location). After tremendous success, i decided to make its big brother hi-gain dual band antenna described here. I tried it 2 times but i failed miserably. this designed didn't work for me (Might be i missed something). So i kept experimenting on that design on hold 🌝🌝🌝.
SDR on Raspberry PI 3B
SDR is my passion. I am a fan of this Software Defined Radio(SDR) technology. During this boring lock-down, I thought to put SDR softwares on a RPI-3B. Well yes there images available to do SDR on RPI. But they are all based on Raspbian. Though i can work on it as I worked on Ubuntu and Armbian. But Fedora is my choice as I have worked with Redhat earlier.
For Experimenting I need to change image often hence first I enabled USB booting on RPI-3B. Then Tried some images. If any of you trying or replicating then do remember fedora is a heavier OS for RPI.
Installing Fedora.
REMEMBER Never jump to load a GUI image directly by downloading.
You know Why I am telling 😅 ......... Yes you are right. So download Fedora minimal image for armhfp from here. Now either use "dd" or use "disk image writer" to create a USB. USB pendrive should be more than or equals to 8GB.
(I downloaded Fedora 31 but you can go for latest Fedora 32 also.)
After making the disk boot from it. Next is to enable wifi. the key is you have only nmcli to configure and setup your network. After you are connected to Internet you need to update the system.
sudo dnf update
next is installing SDR software. basic thing is to install RTL-SDR driver. Its easy just use dnf to install if you are ok with 28MHz and above reception. If you need HF reception without any up-converter , then stock RTL-SDR from fedora repo wont work. For that purpose I will recomend AB9IL . down load it and compile and install it. After installation try rtl_test and rtl_tcp. if you want to use this as remote then you can stop here. Execute
rtl_tcp -a <ip address of RPI> -p <port default is 1234> -s12000
Yes keep sampling rate small as RPI doesn't have much power and wifi is unreliable 😛😛😛. From another machine on the same network use gqrx to connect to your RPI and tune FM stations and of course tune HF to see if you get any... I am sure you will get plenty of Chinese and Arabic stations. I could receive our Local Medium wave station on 972.0KHz only. so you can try your luck.( Note: the sensitivity and frequency range varies from Dongle to Dongle)
Well if you want to venture in to a standalone SDR, then stay with me. The Next step is to put a GUI Desktop environment. One must choose as per his/her personal choice but my experience is bitter with LXQt Gnome and XFCE on RPI-3B. Only LXDE worked smoothly and without much problem. Though i prefere LXQt on my Desktop.
Next is you have to install SDR Radio software like gqrx or CubicSDR. For any SDR software One need a DSP library. liquidDSP andGnuradio are best in my view. GNURadio available from Fedora repo installs Python-2. But GNURadio 3.8 from github uses Pythom-3 hence no old dependencies. So be prepare to compile GNURadio by yourself.
How to compile for RPI?
Well You can compile it on RPI itself but it is never intended. So
1- copy everything to a folder on your desktop PC
2- install qemu-user-static on your pc
3- locate qemu-arm-static
4- copy it in to the folder in point 1
5- use chroot and compile on your PC
Though it is standard method this is slow in comparison to compiling directly on RPI.( Atleast on my Intel(R)Core(TM)2Duo CPU E6750@2.66GHz )
using this process GNURadio, gqrx, LiquidDSP, WxWidget, SoapySDR, SoapySDRserver, SoapySDRremote,soapy-rtlsdr and CubicSDR are compiled.
Please refer to individual compilation process described for respective packages.
Now Copy back the compiled apps to your Pen drive. Boot from it and try executing gqrx and CubicSDR.
Note: May complain about Library not found even after executing ldconfig so adjust /etc/ld.so.conf to include /usr/local/lib
now everything will be fine.
Executing gqrx
Try finding optimum sample rate, band width. Next adjust FFT buffer and speed. Reasonable sound quality will be heard.
Executing CubicSDR
Here multiple settings at multiple areas should be adjusted. Sampling rate, Audo sampling rate and gain to get a good sound quality.
Cheers 73's
DE VU3VFU
