SoftRock Lite - Quadrature Signal Detector (mixer)

Description

The QSD combines the two signals from the second flipflop (phasor) with the 40 meter RF signal from the antenna. The result will be two audio signals that 90 degrees out of phase with each other. These are then passed to the opamp which sends them on to the computer's sound card.

Components - white on schematic

• U4 - FST3253, qsd on the bottom of the board
• R8 - 10 ohm resistor
• R9 - 10 ohm resistor
• R16 - 10k ohm resistor
• R17 - 1k ohm resistor

The back of the board has had U4, the QSD chip, added to it. It is the 16 pin chip in the lower middle of the board.

The four resistors have been added to the front of the board. The red clip lead is attached to R9. R8 and R16 are just to the upper right of it. R17 is below and to the left.

Test

This stage mixes the I and Q oscillator frequencies with the incoming RF. To test it we will inject RF to the leads of R8 and R9. When I attached an antenna to the R8 or R9 I was unable to hear anything. I had to transmit at 7.056 MHz into a dummy load using a QRP transmitter with the clip lead near by. I could hear the transmitted tone as I varied the tranmitter frequency around 7.056 MHz, which indicated that the QSD was working.