SDR Software Defined Radio
What does this do for me?
In a nutshell, SDR allows for limitless filtering and processing of signals. In the past you had rigid hardware limitations on filtering and as an end user, you were stuck with whatever was shipped as production. Changing the options for filtering or demodulation or modulation of the signals was only done with a soldering iron and great effort. SDR allows limitless possibilities at the mere twiddle of a few bits. Of course as all the signal processing and handling is being done at the bit stream and data level, SDR also allows you to capture raw data streams of what you are receiving or transmitting to make further and more flexible options possible.How I Fit In
As a new ham, and one that is rusty in his electronics theory, I'm playing a major game of catch up to understand the nuts and bolts of how my equipment all works. So designing something from scratch, fabricating my own circuit boards and assembling my own transceivers is a fairly unlikely scenario if I intend to build anything particularly useful or powerful. The technology in general has advanced so far that building anything that has cutting edge performance is almost completely ruled out for all but a few that have EE degrees or work in the circuit design field. Also, the component costs have gone through the roof so even with some projects like RF amplifiers where they are still buildable with a little research, the costs are high enough that simply buying something already made can make a lot of sense. With SDR, the leading edge hardware is complex enough that manual assembly is almost out of the question. However, the software is completely accessible. So with a bit of a technical background in systems and dealing with lightweight development and scripting for a number of years, I have found a niche where I can actually dig my fingers in and have some fun with experimentation. This is what the hobby is all about.Hardware
Any SDR will have one form or other of hardware interface. These can range from the most inexpensive kit to much more powerful and complex designs. There are open source platforms and kits and there are commercial turn-key solutions as well. A range to suit most anyone who is interested. At the entry level and definitely a ground breaking project is the Softrock
Softrock Wiki Page
This one can be put together in a few hours in its most basic receive only kits and only requires a soundcard connection to your computer and the open source and freely distributed PowerSDR software. Though it is starting to look like the PowerSDR project is turning its back on the open source community that essentially founded their project, with a trend towards closing things up and breaking compatibility with the projects that have adopted their software.
Luckily, the great thing with open source is that once it is out there, it's free. So there are other projects moving along that will ensure the lifetime of this hardware.
Some more advanced open source SDR projects are...
TAPR's HPSDR Project
This is a modular design with a backplane upon which you add the specific modules you wish to implement. They have a sound card interface, receiver, transmitter and other modules as part of the project. This was one of the first user accessible projects to break through to the more powerful current technology option of using an FPGA allowing for complete re-architecture at will.
GNU Radio and the USRP from Ettus
This is a true experimenter's project. The software is essentially in a building block format where you tie functions together to make the hardware perform as the device you desire it to be.
The QS1R - Quicksilver Project
This one is the one I'm directly associated with. This is the cutting edge of the open source projects that is more of a turn-key hardware approach to a receiver. Among the plans for hardware include a pre-selector/ pre-amp/attenuator module, a QS1T SDR transmitter and other options to come as the project matures.
The Software
The newest software for the QS1R project is called SDRMAXIII and runs cross-platform because it is based on Qt/C++ and the boost libraries. The software is undergoing rapid re-development as it is being ported to the new platform. The hardware development is also proceeding rapidly as compared with the size of the project itself.
This is a screen shot of SDRMAXIII, though an early candidate running on my Ubuntu system. Click for a higher resolution image.
Again, this project can be seen here QS1R Project Wiki