*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)  

To understand why ferrite beads are the correct choice for VHF and UHF parasitic suppressors in a transistor HF amplifier, let's break down each option:

### Correct Answer: Ferrite Beads
- **Function**: Ferrite beads are used to suppress high-frequency noise and unwanted oscillations in circuits. They work by presenting a high impedance to high-frequency signals while allowing lower-frequency signals to pass through.
- **Application**: In the context of VHF and UHF amplifiers, ferrite beads are effective at filtering out parasitic oscillations that can occur at these frequencies, thus improving the stability and performance of the amplifier.

### Why the Other Choices are Incorrect:
1. **Electrolytic Capacitors**:
   - **Function**: These capacitors are primarily used for filtering and decoupling in power supply circuits.
   - **Limitation**: They are not effective at suppressing high-frequency noise due to their relatively high equivalent series resistance (ESR) and inductance at VHF/UHF frequencies.

2. **Butterworth Filters**:
   - **Function**: Butterworth filters are designed to provide a smooth frequency response with no ripples in the passband.
   - **Limitation**: While they can be used for filtering, they are not typically used as parasitic suppressors directly at the input/output terminals of amplifiers. They are more complex and not as effective for suppressing specific high-frequency parasitics.

3. **Steel-Core Toroids**:
   - **Function**: Toroidal inductors can be used for filtering and energy storage.
   - **Limitation**: Steel-core toroids are not suitable for high-frequency applications like VHF/UHF due to core losses and saturation effects. They are more appropriate for low-frequency applications.

### Summary
- **Ferrite Beads**: Best choice for suppressing high-frequency parasitics in VHF/UHF amplifiers.
- **Electrolytic Capacitors**: Not effective for high-frequency noise suppression.
- **Butterworth Filters**: More complex and not used as direct suppressors.
- **Steel-Core Toroids**: Unsuitable for high-frequency applications.

In conclusion, for effective parasitic suppression in VHF and UHF transistor amplifiers, ferrite beads are the most appropriate choice due to their ability to attenuate high-frequency noise while maintaining signal integrity.