SoftRock Lite - Oscillator

Description

The oscillator can be built as the second stage. You could build the amp as the second stage also. The oscillator must precede the divider and QSD stages. This stage will include a crystal controlled Colpitts oscillator (NPN) and a buffer (PNP).

Components - green on schematic

• Q1 - 2N3904, NPN oscillator transistor
• Q2 - 2N3906, PNP buffer transistor
• X1 - 28.224 MHz crystal
• C1 - 0.1uF smt, bottom
• C2 - 0.1uF smt, bottom
• C3 - 100pF
• C5 - 22pF
• R1 - 10 ohms
• R2 - 10k ohms
• R3 - 10k ohms
• R4 - 499 ohms
• R5 - 1k ohms
• R7 - 499 ohms

You can see that two more smt caps have been added to the board. C1 is toward the center of the board, above C9. The test hole to which it is connected, just above it and to the right, is in the 5v trace leading to Q2. You can see this on the top board view. C2 is the upper capacitor on the left side of the board.

For the top board view you can see the oscillator, with Q1, the crystal and other components, clustered in the upper right corner of the board. The buffer, Q2 and other components, are clustered near the power supply in the upper left corner.

Test

The easy way to test this stage involves no physical connections. I use my Grundig Yachtboy 400, which is a general coverage short wave radio with a BFO for sideband (and CW). Tune the radio around 28.224 MHz 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.

When I attached the battery I immediately heard the tone at 28.224 on the Grundig. Be careful here, you may actually zero beat it, hear nothing but see your meter pegged.