Friday, February 9, 2018

Software Defined Radio on OpenBSD


I decided to give my ancient Lenovo S10 netbook another lease on life with a RTL SDR (RTL2832U) radio receiver dongle. I used this little machine for a while as a backup FTP server, but recently replaced with a much smaller Raspberry Pi.  So now it is doing nothing again and can be repurposed.

I would like to automate Weather Fax downloads and got an antenna on the roof, but don't want to risk hooking my Mac up to an outdoor antenna for days on end, since it can get fried when a thunderstorm passes over.  It would be rather less risky to use a Raspberry Pi or an ancient netbook for that!

According to the docs I found online, the rtl_sdr applications do not support rtl_tcp or rtl_adsb on OpenBSD, but maybe it was fixed.  I could make do with rtl_fm to capture the data, then get it with FTP over the WiFi LAN.

First, do an update:
$ su -
password
# pkg_add -u
...long wait...

Finally:
# pkg_add rtl-sdr

To play audio, sound exchange is very handy:
# pkg_add sox
# exit

Now, test things by playing Abu Dhabi Cassic FM:
$ rtl_fm -f 105200k -W  | play -t raw -r 24k -es -b 16 -c 1 -V1 -
...Reading samples in sync mode...

Noisy muzak on my prehistoric netbook - not good enough.

A key thing above is that message about reading samples in sync mode, meaning that reception may be noisy as it may drop packets...

Bah humbug.  My conclusion is that it sorta kinda works on OpenBSD, but I'll have to install a Debian XFCE 32bit i386 version on the netbook to make it work properly with the rtl_sdr utilities.

Eventually, I settled on Ubuntu Linux, which is based on Debian.  However, real Debian would not configure the WiFi adaptor and a computer without ethernet/WiFi is not very useful these days.  Automated download of weather pictures now almost works well enough.   So I need to write a new article about this setup!


La voila!

Herman



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