Question
Why does input attenuation reduce receiver overload on the lower frequency HF bands with little or no impact on signal-to-noise ratio?
Answer Options
- A) The attenuator has a low-pass filter to increase the strength of lower frequency signals
- B) The attenuator has a noise filter to suppress interference
- C) Signals are attenuated separately from the noise
- D) Atmospheric noise is generally greater than internally generated noise even after attenuation
Correct Answer: D
Explanation
Receiver overload is common on the lower HF bands (below about 10 MHz) due to extremely strong broadcast and local signals. Inserting attenuation reduces the strength of all incoming signals, including the unwanted strong ones, thereby mitigating overload in the sensitive front-end stages. A potential drawback is that it also reduces the signal strength of the desired signal, which might seem to harm sensitivity.
However, on the lower HF bands, the signal-to-noise ratio is usually set by atmospheric noise, which is very high and far exceeds the receiver’s own internal noise. Since the receiver’s internal noise is negligible compared to the external atmospheric noise, attenuating the input signal does not significantly degrade the overall signal-to-noise ratio, while successfully alleviating the receiver’s overload problem.
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