SoftRock Lite - Phasor (set to stun)

Description

The phasor stage follows the divider. It is another dual flipflop. The first half of the flipflop will again divide the signal by two. It's the second half of the flipflop that gets tricky. It uses the Q from its first half as the data input and the /Q from the first flipflop as the clock. This produced a signal 90 degrees out of phase from the Q from its first half. So now you have your In phase and Quadrature signals. Let's look at the second and third sets of signals on our diagram.

The second set of signals behaves just like the first set, but this time we are using the Q output signal from the first flipflop to feed the clock of the second flipflop. Again we use the second flipflop's /Q output as its data input. Once again you get a divide by two so that B.Q is now 7056 MHz.

The third set of signals is where it gets interesting. This is the second flipflop on the second chip. It is not being used as a divider. Its clock input is fed with the /Q signal from the first chip (A./Q). Its data input is fed with the Q signal from the first flipflop on the second chip (B.Q). Now when you apply the same rules - Q get whatever the data input is at clock rise, you get the signal at C.Q.

If you look at the schematic you see the QSD (dual mixer) is getting its input from B.Q and C.Q. I have put them side by side in the fourth set of signals and you can see that C.Q trails B.Q by 90 degrees. So you have an In-phase and a Quadrature signal that you will now mix with the incoming RF.

Components - purple on schematic

• U3 - 74HC74, dual flipflop on the bottom of the board

Only the back of the board has had components added, U3, which is the second flipflop. Underneath U3 you see the pads for U4, a 16 pin socket. If you look next to the pads for U4's pin 2 and pin 14 (pad for pin 1 is marked - lower left), you will see that I have soldered in wire test points. This is the destination for the I and the Q signals from U3. When I build the Morgan Logic Probe, I will use those.

Test

Once again this stage can be tested using the Grundig Yachtboy 400. Tune the radio to half what it was before around 7.056 MHz (14.112 / 2) right in the 40m band, and apply power to the Softrock Lite. You should hear the oscillator plainly. You can remove the power, then apply it again to confirm that it is the Softrock that you hear. Of course this only confirms that the first half of the flipflop is doing its divide thing. You will need something a bit more sophisticated to test the I/Q, like a scope, or maybe a $2.49 Morgan logic probe that I have just ordered from Anderson.

I have tested using the Grundig and heard a tone on 7056, so at least the In phase signal is being produced.