HAM Antennas and Feed Lines 5

Question 1

What is the radiation pattern of an isotropic antenna?

Accepted Answer

A perfect sphere — equal radiation in all directions

Answer

A figure-eight pattern in the horizontal plane

Answer

A cardioid pattern with a defined null

Answer

A toroidal pattern with a null off the ends

Question 2

What is the significance of the 1:1 SWR condition on a transmission line?

Accepted Answer

Maximum power transfer occurs with no reflected wave

Answer

All transmitted power is reflected back to the source

Answer

The line radiates exactly half the input power

Answer

The line impedance equals free-space impedance (377 ohms)

Question 3

A log-periodic dipole array (LPDA) antenna is best described as:

Accepted Answer

A broadband directional antenna with moderate gain across a wide frequency range

Answer

A narrow-band, high-gain directional antenna

Answer

An omnidirectional antenna with high gain at all elevation angles

Answer

A circularly polarized antenna for satellite operation

Question 4

What is the effect of ground conductivity on the performance of a quarter-wave vertical antenna with radials?

Accepted Answer

Higher conductivity reduces ground losses and improves radiation efficiency

Answer

Higher conductivity increases the antenna's resonant frequency

Answer

Higher conductivity narrows the antenna bandwidth

Answer

Ground conductivity only affects antennas operating above 30 MHz

Question 5

What is the advantage of using a terminated folded dipole (T2FD) antenna?

Accepted Answer

Broadband operation with low SWR across a wide frequency range due to the terminating resistor

Answer

Very high gain over a narrow bandwidth

Answer

Perfect circular polarization across all HF bands

Answer

Zero radiation resistance for purely reactive operation

Question 6

What is the main advantage of a rhombic antenna over a Yagi for long-distance HF communication?

Accepted Answer

Much broader bandwidth covering multiple HF bands

Answer

Higher gain per element used

Answer

Easier rotation for beam steering

Answer

Lower profile, requiring less real estate

Question 7

What occurs when a transmission line is exactly one half-wavelength long, regardless of its characteristic impedance?

Accepted Answer

The input impedance equals the load impedance (the line is transparent)

Answer

The line presents a short circuit to the source

Answer

The line transforms the load to its complex conjugate

Answer

The SWR at the input doubles compared to at the load