Software Defined Radio

Softrock V5.0


Home Up

This Page is still very much Work in Progress

Software Defined Radio is rapidly growing in popularity. It is a close relation of the Direct Conversion Rx with image rejection. The hardware is pretty minimal as can be seen from the pictures below - the computer takes over all the hard work. The clever guys are working on a companion transmitter.

A couple of of pics showing the small size of the Softrock V5.0 Rx (20m version shown). The American coin is about the size of a 10p piece.

The only connections required for the above are 7-12 volts, an antenna and a stereo connection to the PC Soundcard. I goes without saying that suitable software is required. Two of the more popular offerings are:

Rocky by Alex (VE3NEA) and KGKSDR by Duncan (M0KGK)

A good soundcard is the heart of the system, don't expect your bog standard (integrated on the motherboard) card to give sparkling results, but it will work quite well. For best results a sample rate of 96 kHz (+/- 48 kHz) is needed. With a 7050 kHz Crystal Oscillator that will give almost complete coverage of the 40m band.

A Block Diagram to be inserted here.

Here are are a few MP3 files to be going on with. The recovered audio is remarkably good although the ZL station is very marginal.


RNARS net on 40m


G4UOS signing with G4WZI (40m)


A bit ropey, but ZL2AL is definitely in there. (40m again)

Softrock and the K3.

Recent developments at GM4KGK include the use of a Softrock Lite SDR receiver as a panadapter coupled to the Elecraft K3 transceiver. The wideband K3 IF output is taken to a modified Softrock and fed to KGKSDR software. A buffer amplifier (Z10000 from Clifton Labs) provides isolation to prevent the Softrock crystal oscillator leaking into the K3 IF circuits.

Here are a couple of screen shots.

10 Aug 2008. Late evening 40m CW contest 10 Aug 2008. 18MHz completely dead at 2300Z
Softrock Lite (SR v6.2) with the Clifton Labs Z10000 Buffer Amp. The gain of the buffer has been set to about 7dB to suit an un-modified K3. This can be altered by changing one resistor. A small Maplin box makes a tidy enclosure. Connectors shown are for a 12 v supply and the BNC connection to the K3 IF stages. The stereo connection to the sound card is at the opposite end.