I haven’t blogged much about my Softrock 40 since I finished its construction. I knew that it basically “worked”, but I was pretty sure that the opposite sideband cancellation was quite poor, and I wasn’t thrilled with the various software options that I had available, so it sat on my dining room table for a while. But this weekend was the CQ WPX World Wide CW contest, so I figured the bands would be crowded with CW signals, so I thought I’d dust it off. I also have a new netbook computer that my wife got me for my birthday, so I downloaded Rocky, a recommended application for software defined radio, and gave it a whirl. I was using an EMU 0202 USB sound card, which I was unable to get to work at 96khz, but at 48khz, all seemed well. I recorded 15 minutes of audio to play with, and generally had some fun (I might do a screencast of it sometime in the future), but I also dusted off my program that I wrote, and decoded 15 seconds of the audio, yielding the following on the bottom:

Centered around 7.056 Mhz, decoded with my own software

One of the diagnostics suggests that I am not getting one of the channels at all, which certainly would explain why I am getting no opposite sideband cancellation. I’ll try hooking it up to the oscilloscope and seeing what’s the problem.

If anyone wants to play with the audio I used to generate the stuff above, here’s a link to the 4.1Mbyte file. Let me know what you discover.

Addendum: Yep, one channel is completely dead. Not sure if it is a circuit problem of a cabling problem.

Audio File, normalized, viewed in Audacity

Same file, with Spectrum