The Audacity of Spacecraft

I have no Morse skillz (yet), but I managed to use my iPhone to capture the audio of the CW beacon of the XW-2A cubesat as it passed through the skies to the West of our home, loaded it into Audacity and looked at the waveform to find the signature “CAMSAT” word that the spacecraft includes in its CW transmission:


Too cool 🙂

Raspberry Pi + RTL-SDR Working

First, I used parts of this gist by floehopper to set up rtl-sdr utilities on the Raspberry Pi (already running Raspbian with a 8 GB flash card at its disposal):

pi@raspberrypi ~ $ sudo apt-get update
pi@raspberrypi ~ $ sudo apt-get upgrade
pi@raspberrypi ~ $ vi no-rtl.conf

blacklist dvb_usb_rtl28xxu
blacklist rtl2832
blacklist rtl2830

pi@raspberrypi ~ $ sudo mv no-rtl.conf /etc/modprobe.d/

pi@raspberrypi ~ $ sudo apt-get install git-core
pi@raspberrypi ~ $ sudo apt-get install git
pi@raspberrypi ~ $ sudo apt-get install cmake
pi@raspberrypi ~ $ sudo apt-get install libusb-1.0-0-dev
pi@raspberrypi ~ $ sudo apt-get install build-essential

pi@raspberrypi ~ $ git clone git://
pi@raspberrypi ~ $ cd rtl-sdr/
pi@raspberrypi ~/rtl-sdr $ mkdir build
pi@raspberrypi ~/rtl-sdr $ cd build
pi@raspberrypi ~/rtl-sdr/build $ cmake ../ -DINSTALL_UDEV_RULES=ON
pi@raspberrypi ~/rtl-sdr/build $ make
pi@raspberrypi ~/rtl-sdr/build $ sudo make install
pi@raspberrypi ~/rtl-sdr/build $ sudo ldconfig
pi@raspberrypi ~/rtl-sdr/build $ cd ~
pi@raspberrypi ~ $ sudo cp ./rtl-sdr/rtl-sdr.rules /etc/udev/rules.d/
pi@raspberrypi ~ $ sudo reboot

Then, I added sox (to get the play command):

pi@raspberrypi ~ $ sudo apt-get install sox libsox-fmt-all

I hooked up a speaker to the Raspberry Pi audio port and then tuned and listened to Puget Sound’s favorite packet frequency:

rtl_fm -f 144390000 -M fm -s 12k - | play -r 12k -t s16 -L -c 1 -

Worked nicely. Need to add squelch argument and combine this with the demodulator I’ve been working on.  Satellite tracking with automatic recording of space station packets is the ultimate goal.

Preamp Progress

I’m making progress on the 440 MHz preamp kit.  Should be up and running soon.  Will make hearing the 70cm satellites a lot easier I hope.  (The kit is by Ramsey, fancy aluminum case by Hammond.)


That Happy Moment When

the demodulator you’ve been working on starts outputting meaningful data instead of gibberish (T7RPUR WIDE1 WIDE2 are valid packet radio strings).

Screen Shot 2015-08-24 at 8.45.48 AM

I’m writing the demodulator in C++ and it uses the Goertzel algorithm.  Need to continue to flesh out the framer, and hook up STDIN to accept sound from rtl_fm and my new SDR dongle.

The goal: automated reception of Space Station packet radio, powered by Raspberry Pi.

First WX Image from NOAA-18

I received my first WX image from NOAA-18 as it passed overhead just a few moments ago.  I was alerted to the pass by the Raspberry Pi based ground station-in-a-box I’ve been working on (far left in the picture) and used the WXtoImg software (center) to decode the signal from my radio, piped through the sound card box I like to use.

FullSizeRender 9

This was with a simple 2m J Pole antenna, but I plan to build an eggbeater or maybe a helical antenna soon.  I need to build a pre-amp too I think.

Here’s a video of what it all sounded like

Here’s my final image:


and an image from about the same time from the NOAA website for comparison: