Christoph Petermann DF9CY 2006

Status: Receiver is working as expected.
Last Revision: 10 October 2006

Intention

I wanted to 'play' with a SDR = Sftware Defined Radio. I listened to a talk of OM Bodo Scholz DJ9CS on 1 May 2006 he gave in Eckernförde. It took me some time but in September I ordered a kit for me. After completion it worked immediately and with software like WINRAD and ROCKY I was able to receive first signal on the 40m quickly. Next test was DRM, but therefore I had to remove the crystal and feed from an external oscillator. Quickly done I could almost immediately decode DRM signals using the reknown DREAM software.

Next step will be putting the circuit into a tiny box with switches for internal and external oscillator feed and /4 and /8 divider.

Images of my Softrock Version 6.1

Topside view
You may find R5 is missing... I made some slight changes. See below. The lead parts are replaced by SMD devices on the bottom side.

Bottom Side View

Schematic Diagram of the Softrock Receiver

Changes made to the original schematic

I wanted to try to feed the oscillator signal with an external generator. I desoldered the 28.226 MHz crystal and replaced it with a socket and a small capacitor in series feeding the RF signal into the base of Q1. The biasing of Q2 had to be changed giving the posibility of feeding with an RF signal of about 150mV.


R5 is left open and R17 is 440KOhm and the coupling capacitor is 100pF now. This is a LTSpice (SwitcherCad) simulation. The component designators here are different to the original. Take care.


Here The input and output waveforms are shown. This is SwitcherCad simulation.

Sources

DJ9CS : SoftRock: Ein Einstieg in die Technolgie des 'Software Defined Radio' (SDR)

Softrock YahooGroup