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The above sine wave begins to distort or pull below 140 hz as harmonics enrich the low end sound. Higher up in frequency the wave shape in this display become closer together and pointier. A soft ramp wave below 140 hz is excellent.

The two RF oscillators create signals that blends together at the D2 diode.

I call this interaction talking to one another. One form of talking is RF radiation or EMF and the other is capacitive coupling between all of the components. The grounded shield around the IFT  L1 coil mainly prevents capacitive coupling between the coils. This is why it is good to use a ground plate shield under the L1 oscillator. While this grounding works quite good, the other components like copper traces, circuit wiring and transistors also talk.

The oscillators on the Pitch board need to whisper to one another as this is the level we want our heterodyne mixing to occur at D2. If you look closely, the L1 & L2 circuits are not connected to one another in any way. The D2 diode detects this whisper the same way a crystal radio detects the audio signal from a radio wave.

Note: It is important on your final tuning on both boards to be in-between any AM Radio stations. Use an analog AM Radio tuned properly to determine this.

When the antenna and earth ground is attached to the Pitch oscillator board at L2 the L1 side of the pcb gets screamed at by the extra antenna RF and the increased capacitance coupling surface area. This is what the ground plate helps quiet down.

L1 is already naturally grounded through variable Pot-5. This Pot allows the IFT shield ground to be variable so we can use this as an adjustable effect on the final audio wave shape.

It is best to avoid any shielding or grounding around the L2 side of the PCB as this might affect the inside pitch field linearity. In other words,  normally do not connect Terminal A to anything.

Visit Step #2   Finishing the Pitch Section Components