So I thought it was time to become familiar with the ham phenomenon known as software defined radio. In very vague terms, a software defined radio mixes the incoming RF down to baseband phase and quadrature (I and Q) signals, fed to a computer sound card and software does the rest of the demodulation. The opposite happens for transmit.
I chose the Softrock Lite+USB Xtall v9.0 kit -- it uses a Si570 programmable oscillator controlled by an AVR connected to a USB port as the local oscillator. It is receive only, 160-10m, and does not transmit.
I spent an enjoyable afternoon to building and testing the board. No problems were encountered during the build. It just went together and worked. A great combination of detailed step-by-step or high-level hand-wavy instructions are available at the WB5RVZ website.
The kit is a nice mix of THM and SMD parts. I use a Metcal soldering station and a 10x stereo magnifier for all parts and final inspection.
The extra boards are plug-in bandpass filters. There is an option for an automatically switched bandpass filter, but I didn't opt for that, it would be a cool option, though. I haven't yet wound the 160m board -- a combination of needing to wind a million turns on a tiny little core and having never made a qso on that band before means it just hasn't happened.
Does it work? Well, it can receive me just fine when I'm transmitting into a dummy load nearby. But I don't actually have an outdoor antenna, so I have yet to decode any off-the-air signals.
Computer and sound-card wise I've tried a few different things. My 1.2GHz PIII laptop with built-in soundcard doesn't work well. Undoubtedly it's the soundcard. My 1GHz PIII shop computer has a pair of soundcards. The SB Live! card works OK with Rocky at 48kHz (card max). My regular desktop PC with a Core2 processor and EMU-0404 USB external sound card (192kHz sample rate) runs PowerSDR no problem.
Next up, I'll have to try my emu0404 with my laptop and try from W9YT. From there I'll be able to compare with a Yaesu FT847 and Kachina KC505.
Mon Jan 12 13:37:47 CST 2009
Connected to a real antenna at W9YT. Works. Didn't get a chance to listen much as I had to swap the audio cable. Had the opportunity to use a new-ish Weller WES51 for this task. What a piece of crap. Do people actually wait for their soldering irons to heat up and then the solder to melt? I'll take my Metcal anyday.
I need to calibrate the frequency of the Si570. Mine's off by a little bit.
This page last modified Mon Jan 12 13:54:37 CST 2009 by timc!