Question 4A5

VHF radio receivers often use Frequency Modulation (FM). In an FM receiver, the **capture effect** occurs when two signals are present at the receiver's input on the same frequency. The stronger signal "captures" the receiver, completely suppressing the weaker signal. This suppression happens prominently at the **limiter stage**, which is designed to remove amplitude variations, essentially "choosing" the stronger signal. Thus, a weak desired signal can be prevented from being received if a stronger, perhaps undesired, signal is also present. A) This describes the normal operation of a superheterodyne receiver, converting the incoming RF signal to an Intermediate Frequency (IF) for processing. This is how signals *are* received, not prevented. B) If the PLL in the frequency synthesizer becomes unlocked, the receiver would lose its tuning stability and likely fail to receive *any* signal properly, not just a weak one specifically due to another signal. C) This describes amplification, which is the intended function of an AF (audio frequency) amplifier stage, making the signal audible. It is a necessary part of reception, not a preventative condition.