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SDR Software Project

The idea is to create the software side of SDR for the average ham without a lot of specialized equipment. The SDR hardware is a Tony Parks SoftRock Lite that only costs $10.

Component List:

  • "Dumpster grade" PC - a P3 class PC (700 - 900 MHz, 512 Mb RAM)
  • low end 24 bit soundcard - SoundBlaster Live 24
  • free operating system - Linux (I'm working with Kubuntu)
  • LinRad software -OR-
  • DttSP with SDR Shell

Resources:

Roger Rehr, W3SZ, has a website full of articles on Digital Signal Processing and SDR in particular. W3SZ Home Page Use his site for installing Linrad into Ubuntu/Kubuntu. Leif Asbrink, SM5BSZ, is the creator of Linrad. Check out his Linrad Home Page

Progress:

  • I have a Dell Optiplex GS-110 small form factor PC with 512 Mb RAM and an 866 MHz processor. Will replicate on a Dell Optiplex GS-110 tower PC with 512 Mb RAM and a 733 MHz processor.
  • I have added a SoundBlaster Live 24 sound card to both.
  • I have Kubuntu 6.06 (Dapper Drake) running on both.
  • I installed Linrad on the small form factor Optiplex following W3SZ's instructions. It was very easy using the Apt utility on Kubuntu. I set up the parameters, also following W3SZ's instructions. I then attached the SoftRock Lite and was immediately able to listen to CW. I could detect PSK and SSB, and didn't notice any images. So I think it runs okay on the "dumpster grade" PC. But there is a lot to learn about using Linrad.

After some advice from Roger and a lot of playing, I think Linrad is working reasonably well. Right now I have the following "U" selections made: 

01:  /dev/dsp1    1000 -   192000 Hz  4 Chan.  16 bit RDONLY WRONLY RDWR (internal)
63:   /dev/dsp    1000 -   192000 Hz  4 Chan.  16 bit RDONLY WRONLY RDWR (SB Live 24)
Select device for input by first number on line 63

Open /dev/dsp as TDONLY or RDWR? (O/W)  => O

Select radio interface:
1: One rx channel (normal audio)
2: One rx channel I/Q (direct conversion rx)
3: Two rx channels (adaptive polarisation/phasing)
4: Two rx channels I/Q
4

Select sampling speed(1000 to 192000)   48000

Use close and repoen for D/A when a new signal is
selected or when the output device fails? (Y/N) N
One of the most helpful tricks for me was to run the SRLite with the antenna disconnected. Because these soundcards aren't perfect there will be a noise hump at the center frequency, in our case 7.056 MHz. By disconnecting the antenna that's almost the only think that will show up on the spectrum, (unless there's a digital contest going on. I got RTTY with no antenna!) You can use the top right arrows to center the noise hump in the spectrum and waterfall. Here is a screen print of my latest efforts.

Linrad1.jpg

The colorful line going across the waterfall about 1/3 of the way down is where I disconnected and reconnected the battery. The hottest spot, the white dot on that line is 7.056 MHz. The vertical line going through that white spot is the center frequency noise line. Looking at the vertical lines you can see some image, but they are definitely reduced. The white line on the spectrum is where I was currently listening. The further from center, the less the image is reduced.