HAM Antennas and Feed Lines 3

Question 1

What is the characteristic impedance of open-wire (ladder) line typically used with balanced antenna tuners?

Accepted Answer

300 to 600 ohms

Answer

Open-wire or ladder line has a characteristic impedance typically ranging from 300 to 600 ohms depending on conductor spacing and diameter.

Question 2

What is the effect of adding a director element to a Yagi antenna in front of the driven element?

Accepted Answer

It increases the front-to-back ratio and forward gain

Answer

A director, being slightly shorter than the driven element, re-radiates energy forward, increasing forward gain and front-to-back ratio.

Question 3

What is a loading coil used for in a shortened mobile HF antenna?

Accepted Answer

To add inductance and resonant the electrically short antenna

Answer

A loading coil adds the inductance needed to resonate an electrically short antenna at the desired operating frequency.

Question 4

What is the input impedance of a quarter-wave matching section (Q-section) used to transform a 200-ohm antenna to 50 ohms?

Accepted Answer

100 ohms

Answer

The characteristic impedance of a quarter-wave matching transformer equals the geometric mean: √(50 × 200) = 100 ohms.

Question 5

What is the approximate gain of a three-element Yagi antenna relative to a dipole?

Accepted Answer

5 dBd

Answer

A well-designed three-element Yagi typically achieves approximately 5 dBd (5 dB gain over a dipole) of forward gain.

HAM - Radio Extra Class Test Practice Test