*Question E6D09:
What devices are commonly used as VHF and UHF parasitic suppressors at the input and output terminals of a transistor HF amplifier?*  

*Correct Answer is  C: Ferrite beads*  

### AI Response: (may contain errors)  

Ferrite beads are commonly used as VHF and UHF parasitic suppressors at the input and output terminals of a transistor HF amplifier. Here's why:

1. **Correct Answer: Ferrite Beads (C)**
   - **Purpose**: Ferrite beads are used to suppress high-frequency parasitic oscillations. They act as lossy inductors at VHF and UHF frequencies, which helps to dampen unwanted signals that can cause instability in amplifiers.
   - **Functionality**: By increasing the impedance at high frequencies, ferrite beads effectively reduce the gain of parasitic frequencies, stabilizing the amplifier.

2. **Why Other Choices Are Incorrect:**
   - **Electrolytic Capacitors (A)**: These are used for energy storage and filtering at low frequencies, not for suppressing high-frequency parasitics. They are not effective at VHF and UHF frequencies due to their high equivalent series resistance (ESR) and inductance.
   - **Butterworth Filters (B)**: These are designed for specific frequency filtering applications, providing a flat frequency response in the passband. They are not used as parasitic suppressors because they do not inherently dampen unwanted oscillations.
   - **Steel-core Toroids (D)**: While toroids can be used for inductance, steel cores are not suitable for high-frequency applications due to their high losses at VHF and UHF frequencies. Ferrite cores are preferred for these frequencies.

In summary, ferrite beads are the most effective choice for suppressing VHF and UHF parasitic oscillations in transistor HF amplifiers due to their ability to increase impedance and dampen unwanted high-frequency signals.