KB9YIG's Soft Rock 40


These pages document some of the experiments I've done with KB9YIG's Soft Rock 40 receiver. Some of these were done with versions of the Soft Rock that pre date the kit AmQRP is currently selling, so some of the pictures and diagrams on this site do not match the kit from AmQRP. The basic circuits are valid for the AmQRP version of the Soft Rock, but some of the component names and board layout details on these pages do not match the level 4.0 board that AmQRP is kitting.

The AmQRP Soft Rock page can be found at http://amqrp.org/kits/softrock40/index.html

There's also a very active Soft Rock Group on Yahoo Groups. This group is essential reading for folks experimenting with Soft Rock style receivers.

Update 13 March 2006:First look at Soft Rock V6 can be seen here.


I've modified Flex-Radio's PowerSDR software to work with the Soft Rock 40. The combination of the relatively simple Soft Rock 40 hardware with the PowerSDR software results in a low cost receiver with some very nice features. It is a very effective demonstration of the capabilities of the software defined radio approach.

Flex-Radio is now (version 1.4.5 pre 2) including my changes to support the Soft Rock in their PowerSDR distribution. PowerSDR can be downloaded from the Flex-Radio's site

The latest code I've released for the Soft Rock 40 can be found here.

There are at least five other programs that can be used with the Soft Rock. They are:

  • Rocky by Alex (VE3NEA)
  • SharpDSP Mini Console by Phil Covington (N8VB)
  • Duncan's (M0KGK) KGKSDR
  • SDRadio from Alberto (I2PHD)
  • Winrad also from Alberto (I2PHD)

    These are all very good programs, and I'd encourage folks to try them out.

    Soft Rock Mods and Circuits, V5 prototype, V6 prototype, Spice Modelling

    Some of the circuits and analysis I've done with the Soft Rock:

  • SoftRock, DDS, Atmel AVR Butterfly lash up
  • A Frequency Doubler for the Soft Rock and NJQRP DDS card
  • Some photos of my Version 5 alpha build of the Soft Rock.
  • Spice Modelling of the Version 5 quadrature generation circuit
  • Some scope traces of the SoftRock V5 waveforms
  • Some pics of the SoftRock V6
  • Some pics and spectrum shots of a Pre-Alpha Soft Rock v7
  • Pics and spectrum shots of a beta level Soft Rock 7
  • Pics and spectrum shots of a production level Soft Rock 6 on 80/40 meters
  • Some initial experiments with a harmonic sampling SR 6 for 40 and 20 meters
  • Pictures of the V6 exciter stack boards

  • Future Possibilities

    Further integration of a DDS and a micro controller with a Soft Rock 40 would allow for an inexpensive full band coverage SDR type receiver. Integration with a USB based sound chip, and a USB capable micro controller would allow for an SDR with 1 connection to the computer, and one to an antenna. It should be able to cover 30 and 40 meters without having to change the input filter, to get on 20 or 80 should be doable with a suitable tweak to the input bandpass filter.

    On the software side, I'm hoping to try this setup with some 96 and 192 kHz sampling rate sound cards. Also need to check out I2PHD's SDRADIO with this hardware.

    Thanks and Acknowledgements

    This has been a fun project to put together. Thanks to Tony Parks (KB9YIG) for the Soft Rock 40 circuit and board design. Thanks to Gerald Youngblood (K5SDR), Bob Mc Gwier (N4HY) and Frank Brickle (AB2KT) for the GPL licensed PowerSDR and DttSP software. Thanks to Steve Weber (KD1JV) for publishing his Butterfly DDS code, and to the NJ QRP folks for the DDS card. Also thanks to all the Flex Radio Friends on Team Speak that tossed out ideas on building a simple SDR receiver.

    Comments to: Bill Tracey (kd5tfd@ewjt.com)

    Last Updated 23 April 2006

    Copyright © Bill Tracey 2005,2006