Which of the following is used to shunt feed a grounded tower at its base?
The correct answer is C: Gamma match. A gamma match is used to shunt feed a grounded tower at its base. The gamma match allows feeding a grounded structure (like a tower) as an antenna.
When using a tower as an antenna, the tower is grounded at its base. A gamma match connects to the tower - the shield connects to the tower base (ground), and the center conductor connects to a point up the tower (a fraction of a wavelength). This allows the grounded tower to be fed and used as an antenna. The gamma match provides the impedance transformation needed to match the tower's impedance to the feed line. This is a common technique for using existing towers as antennas, especially for low-frequency bands where full-size antennas are very large.
Exam Tip
Shunt feed grounded tower = Gamma match. Remember: Gamma match is used to shunt feed a grounded tower at its base - the shield connects to ground, and the center conductor connects to a point up the tower.
Memory Aid
"**S**hunt **F**eed **T**ower = **G**amma **M**atch (think 'SFT = GM')"
Real-World Application
You want to use your 100-foot tower as a 160-meter antenna. The tower is grounded at its base. You install a gamma match - the coax shield connects to the tower base (ground), and the center conductor connects to a point up the tower (maybe 30-40 feet up). This allows the grounded tower to be fed and used as an antenna.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Double-bazooka match is a different technique, not typically used for shunt feeding grounded towers.
Option B: Incorrect. Beta or hairpin match requires an insulated element, not suitable for a grounded tower.
Option D: Incorrect. Not all options are correct. Only gamma match is commonly used for shunt feeding grounded towers.
题目解析
The correct answer is C: Gamma match. A gamma match is used to shunt feed a grounded tower at its base. The gamma match allows feeding a grounded structure (like a tower) as an antenna. When using a tower as an antenna, the tower is grounded at its base. A gamma match connects to the tower - the shield connects to the tower base (ground), and the center conductor connects to a point up the tower (a fraction of a wavelength). This allows the grounded tower to be fed and used as an antenna. The gamma match provides the impedance transformation needed to match the tower's impedance to the feed line. This is a common technique for using existing towers as antennas, especially for low-frequency bands where full-size antennas are very large.
考试技巧
Shunt feed grounded tower = Gamma match. Remember: Gamma match is used to shunt feed a grounded tower at its base - the shield connects to ground, and the center conductor connects to a point up the tower.
记忆口诀
**S**hunt **F**eed **T**ower = **G**amma **M**atch (think 'SFT = GM')
实际应用示例
You want to use your 100-foot tower as a 160-meter antenna. The tower is grounded at its base. You install a gamma match - the coax shield connects to the tower base (ground), and the center conductor connects to a point up the tower (maybe 30-40 feet up). This allows the grounded tower to be fed and used as an antenna.
错误选项分析
Option A: Incorrect. Double-bazooka match is a different technique, not typically used for shunt feeding grounded towers. Option B: Incorrect. Beta or hairpin match requires an insulated element, not suitable for a grounded tower. Option D: Incorrect. Not all options are correct. Only gamma match is commonly used for shunt feeding grounded towers.
知识点
Gamma match, Shunt feed, Grounded tower, Tower antenna
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.