What is downfade in RF signals?

What is downfade in RF signals?

• A. Degraded signals arriving at the receiver, often due to multipath effects.
• B. Signal strength increasing due to constructive interference.
• C. A phase shift that does not affect amplitude.
• D. A calibration error in the transmitter.

Answer: (A)

Downfade is the drop in received RF signal strength caused by destructive interference from multiple propagation paths. In radio propagation, a transmitted signal often reaches the receiver through various paths—direct, reflected, diffracted, or scattered. Each path has its own amplitude and phase, and when these components combine, they can cancel each other out if they arrive out of step. This partial or complete cancellation lowers the net signal amplitude at the receiver, producing a faded or degraded signal. This fading can vary with time as the relative phases change with movement, and with frequency as different wavelengths interact differently. The other ideas describe different concepts: constructive interference would boost signal strength rather than weaken it; a phase shift by itself might change the signal’s timing but doesn’t necessarily change amplitude; a calibration error is not the propagation effect causing fading.

Downfade is the drop in received RF signal strength caused by destructive interference from multiple propagation paths. In radio propagation, a transmitted signal often reaches the receiver through various paths—direct, reflected, diffracted, or scattered. Each path has its own amplitude and phase, and when these components combine, they can cancel each other out if they arrive out of step. This partial or complete cancellation lowers the net signal amplitude at the receiver, producing a faded or degraded signal. This fading can vary with time as the relative phases change with movement, and with frequency as different wavelengths interact differently.

The other ideas describe different concepts: constructive interference would boost signal strength rather than weaken it; a phase shift by itself might change the signal’s timing but doesn’t necessarily change amplitude; a calibration error is not the propagation effect causing fading.