Which is generally true for 160- and 80-meter receiving antennas?
The correct answer is A: Atmospheric noise is so high that directivity is much more important than losses. For 160- and 80-meter receiving antennas, it's generally true that atmospheric noise is so high that directivity is much more important than losses. The high noise floor means signal-to-noise ratio is the limiting factor, not losses.
On 160 and 80 meters, atmospheric noise (from lightning, etc.) is very high - often the dominant noise source. This high noise floor means that even if your antenna has some losses, the signal-to-noise ratio is primarily determined by how well the antenna rejects noise from unwanted directions (directivity), not by the losses themselves. A directional antenna that rejects noise from most directions is much more valuable than a lossless omnidirectional antenna that receives noise from all directions. This is why Beverage antennas and other directional receiving antennas are popular on these bands.
Exam Tip
160/80m receiving = Directivity more important than losses. Remember: On 160 and 80 meters, atmospheric noise is so high that directivity (rejecting noise) is much more important than antenna or feed line losses.
Memory Aid
"**1**60/**8**0m **R**eceiving = **D**irectivity > **L**osses (think '160/80mR = D>L')"
Real-World Application
You're operating on 160 meters. Atmospheric noise is very high. You have two options: a lossless but omnidirectional antenna, or a Beverage antenna with some losses but high directivity. The Beverage is much better because it rejects noise from unwanted directions, improving your signal-to-noise ratio. The losses are less important than the directivity.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Receiving antennas don't need to be 1/2 wavelength above ground for good directivity. Beverage antennas work well mounted low.
Option C: Incorrect. While low-loss coax is always good, on 160/80 meters, directivity is more important than feed line losses because atmospheric noise dominates.
Option D: Incorrect. Not all options are correct. Only the directivity vs losses statement is generally true for these bands.
题目解析
The correct answer is A: Atmospheric noise is so high that directivity is much more important than losses. For 160- and 80-meter receiving antennas, it's generally true that atmospheric noise is so high that directivity is much more important than losses. The high noise floor means signal-to-noise ratio is the limiting factor, not losses. On 160 and 80 meters, atmospheric noise (from lightning, etc.) is very high - often the dominant noise source. This high noise floor means that even if your antenna has some losses, the signal-to-noise ratio is primarily determined by how well the antenna rejects noise from unwanted directions (directivity), not by the losses themselves. A directional antenna that rejects noise from most directions is much more valuable than a lossless omnidirectional antenna that receives noise from all directions. This is why Beverage antennas and other directional receiving antennas are popular on these bands.
考试技巧
160/80m receiving = Directivity more important than losses. Remember: On 160 and 80 meters, atmospheric noise is so high that directivity (rejecting noise) is much more important than antenna or feed line losses.
记忆口诀
**1**60/**8**0m **R**eceiving = **D**irectivity > **L**osses (think '160/80mR = D>L')
实际应用示例
You're operating on 160 meters. Atmospheric noise is very high. You have two options: a lossless but omnidirectional antenna, or a Beverage antenna with some losses but high directivity. The Beverage is much better because it rejects noise from unwanted directions, improving your signal-to-noise ratio. The losses are less important than the directivity.
错误选项分析
Option B: Incorrect. Receiving antennas don't need to be 1/2 wavelength above ground for good directivity. Beverage antennas work well mounted low. Option C: Incorrect. While low-loss coax is always good, on 160/80 meters, directivity is more important than feed line losses because atmospheric noise dominates. Option D: Incorrect. Not all options are correct. Only the directivity vs losses statement is generally true for these bands.
知识点
160/80 meters, Receiving antennas, Atmospheric noise, Directivity vs losses
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.