In a self excited oscillator, what will a swinging antenna cause?

• A. Serious frequency instability
• B. No noticeable frequency instability
• C. Minor frequency instability
• D. None of the above

Answer: (A)

In a self-excited oscillator, a swinging antenna can lead to serious frequency instability due to changes in the loading effects on the oscillator's circuit. When the antenna moves, it alters the impedance of the system, which can affect the resonant frequency of the oscillator. This instability arises because the oscillation frequency is highly sensitive to both the physical arrangement of the components and the electrical characteristics of the load connected to the oscillator.

As the antenna swings, the variations in orientation and distance from surrounding objects can cause shifts in reactance and resistance. Such variations introduce fluctuations in the phase and amplitude of the feedback signal, ultimately leading to an unstable frequency output. This is especially critical in radiotelegraph communications where consistent frequency is vital for effective transmission and reception.

The other options indicate varying degrees of stability, which do not accurately encompass the significant impact a swinging antenna has in disrupting the oscillator's operation. Thus, serious frequency instability is the most fitting conclusion given the nature of the components involved in a self-excited oscillator system.