It has now been eight years since I have retired my Hy-Gain DX-88 antenna declaring it dead for good. I was standing with a broken base element for the second time and I decided not to spend any more time and money on it but try a new antenna, a Butternut HF2V covering 160, 80, 40 and 30 meters.
It looks like AMSAT is going to launch a new satellite! ARISSat-1 – the successor of SuitSat-1 – is ready to be launched on Progress-41P heading to the International Space Station on Friday, January 28, 2011. It will be deployed into its own orbit during EVA 27 currently scheduled for February 16. Once in orbit, it will slowly decay and eventually burn up in the Earth’ atmosphere. SuitSat-1 decayed after 7 months in orbit and that’s also a likely life time for ARISSat-1.
So, why is ARISSat-1 cool and why should we care?
On July 10, 2010, I was listening to the linear transponder downlink of VO-52 when I suddenly noticed a very strong peak about 50 kHz below. I checked Gpredict and found out that it was the APRS downlink from the International Space Station RS0ISS on 145.825 MHz. Thanks to the flexible GNU Radio framework and the USRP, I could easily receive both satellites at the same time as shown on the video below.
New update of the simple receiver – version 0.6 – with the following changes:
- Added frequency entry widget to change USRP frequency
- Also created AM and narrow FM versions
Today I felt like doing an experiment that is not quite on my TODO list – a binaural CW receiver. A binaural CW receiver is a receiver that gives a spatial feeling while you are tuning. As I understand it, you have to use stereo where the signals move from one side to the other as you tune and are in the middle when you are tuned to the frequency.
Few days ago I wrote about how I upgraded the simple double side band receiver implemented in the GNU Radio Companion to a simple single side band receiver. This initial implementation used some default values for the AGC attack and decay rates. These values were acceptable; however, I wanted to spend some time trying to find better values that would correspond to Fast, Medium and Slow AGC – just as we are used to in commercial radios.
Tonight I have been testing some ham radio transceiver code written in Python/GNU Radio. It is some student project published on SourceForge. You can find the code on the project page at Sourceforge: http://sourceforge.net/projects/sdr.
The way I achieved it was by configuring Fldigi to capture its data using the built-in microphone and turn the volume in Web SDR up until it was sufficient. The result was surprisingly good; of course partly because the Mac has relatively good sound hardware – at least when compared to some standard PC sound chip.
I prepared this video demonstrating how it works. You will hear and see many PSK-31 stations as well as some RTTY and other modes. Enjoy and have fun.
Watch in high resolution.
This page provides an overview of the various projects and experiments I am or have been doing with GNU Radio and the Universal Software Radio Peripheral (USRP). GNU Radio is a free, open source software development toolkit that provides the signal processing runtime and processing blocks to implement software defined radio. The USRP provides a flexible and cost efficient hardware platform that can be used with GNU Radio to convert the digital data to radio frequencies and vice versa. The USRP and various RF daughterboards, covering most of the DC to 6 GHz spectrum, can be purchased from Ettus Research. Schematics and firmware sources are available under open source license.
My projects with GNU Radio and the USRP are in the field of amateur radio and space communications. The idea is to achieve a broad range of functionality by using different hardware and software configurations. For example, using the same hardware I can switch between narrow band voice communications (SSB/FM) and digital high definition video broadcast using 8 MHz bandwidth by simply switching the signal processing software.
- Gnu Radio Companion Examples
- Gqrx AM, FM, SSB, AFSK, BPSK receiver powered by GNU Radio and Qt
- Simple DVB setup
More GNU Radio / USRP hardware and software projects will be added as they become available. You can also follow my GNU Radio blog if you want to keep up to date with my work in this area (dedicated RSS or Atom feeds available), or you can view the complete blog archive.
I hope these projects demonstrate the power of open source hardware and software.