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Subelement G9
Antennas and Feed Lines
Section G9D
Specialized antennas
Which of the following antenna types will be most effective as a Near Vertical Incidence Skywave (NVIS) antenna for short-skip communications on 40 meters during the day?
  • Correct Answer
    A horizontal dipole placed between 1/10 and 1/4 wavelength above the ground
  • A vertical antenna placed between 1/4 and 1/2 wavelength above the ground
  • A left-hand circularly polarized antenna
  • A right-hand circularly polarized antenna

The idea of an NVIS antenna is to use the proximity to ground to reflect a lot of the signal up, rather than out. If it were higher, like 1/2 wave, it would radiate horizontally, out rather than up. If you're trying to work DX, get your dipole up high. To work local stations on 40m during the day and 80m at night, keep it low.

Right and left-hand polarization have nothing to do with NVIS.

Hint: The Near Vertical Incidence Skywave needs a horizontal dipole.

Silly Hint: 40 = 10x4. The answer contains 10 and 4

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What is the feed-point impedance of an end-fed half-wave antenna?
  • Very low
  • Approximately 50 ohms
  • Approximately 300 ohms
  • Correct Answer
    Very high

EFHW antennas often have feed point impedance as high as 2500 ohms or greater. Often a 49:1 Unun or some other type of match is used at the feed point to match to standard feed lines (50/450/600 ohm feeds)


Hint: One source stated that it’s very difficult to predict the impedance of an end-fed wire, other than to say it's high. Usually it's determined empirically.

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In which direction is the maximum radiation from a portable VHF/UHF "halo" antenna?
  • Broadside to the plane of the halo
  • Opposite the feed point
  • Correct Answer
    Omnidirectional in the plane of the halo
  • Toward the halo's supporting mast

Halo antennas are usually horizontally polarized (the plane of the halo is horizontal, or parallel to the ground) - so they radiate in all directions, but horizontally instead of vertically polarized.

In areas where horizontal polarization is preferred, the halo is sometimes used mobile.

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What is the primary purpose of antenna traps?
  • Correct Answer
    To permit multiband operation
  • To notch spurious frequencies
  • To provide balanced feed-point impedance
  • To prevent out-of-band operation

The primary purpose of antenna traps is to permit multiband operation.

Resonant LC circuits are used in parallel to isolate sections of the antenna effectively changing the antenna's "electrical length". This allows the antenna to be used for several bands rather than one static wavelength.

SILLY HINT: Antenna traps and multiple bands

For more info see Wikipedia: Antenna (radio)_Bandwidth

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What is an advantage of vertical stacking of horizontally polarized Yagi antennas?
  • It allows quick selection of vertical or horizontal polarization
  • It allows simultaneous vertical and horizontal polarization
  • It narrows the main lobe in azimuth
  • Correct Answer
    It narrows the main lobe in elevation

The advantage of vertical stacking of horizontally polarized Yagi antennas is that it narrows the main lobe in elevation.

The resulting narrowing of the vertical width of the main lobe results in an increase in gain, with stronger received signals and less noise.

Suggest: 'vertical stacking', vertical - phrase for elevation

For more information see Wikipedia: Yagi antenna

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Which of the following is an advantage of a log periodic antenna?
  • Correct Answer
    Wide bandwidth
  • Higher gain per element than a Yagi antenna
  • Harmonic suppression
  • Polarization diversity

An advantage of a log periodic antenna is wide bandwidth.

In this type of multi-element directional antenna, the lengths of the elements and the spacing among them are both arranged in a log-periodic manner. This allows the antenna to be operated consistently over a large range of frequencies.

Hint: A log is wide.

For more info see Wikipedia: Log periodic antenna

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Which of the following describes a log periodic antenna?
  • Correct Answer
    Element length and spacing vary logarithmically along the boom
  • Impedance varies periodically as a function of frequency
  • Gain varies logarithmically as a function of frequency
  • SWR varies periodically as a function of boom length

A log periodic antenna is described as one in which the length and spacing of the elements increases logarithmically from one end of the boom to the other.

The advantage of this type of antenna arrangement is that it allows operation over a wide range of frequencies, rather than one static frequency band.

Memorization aid: "log" in the question = "logarithmically" in the correct answer

The word "logarithmically" appears in 2 answers; For me better to remember "log" in the question = "log - boom" in the correct answer

For more info see Wikipedia: Log periodic antenna

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How does a "screwdriver" mobile antenna adjust its feed-point impedance?
  • By varying its body capacitance
  • Correct Answer
    By varying the base loading inductance
  • By extending and retracting the whip
  • By deploying a capacitance hat

“Screwdriver” antennas are vertical antennas with a usually built-in impedance matching mechanism. These antennas function by using a large motor at the base of the antenna to raise and lower a decoupler against the windings of an inductor, usually hidden underneath a plastic tubing.

The decoupler is essentially acting as a tap for the inductor. Wherever the decoupler is sitting, this will result in the different tuning of the antenna.

Lower bands, such as 80 and 160, will result in being able to see more of the coils (inductor).

With higher bands, the antenna climbs up the inductor, resulting in lower inductance.

Amateur Radio Wiki: Screwdriver Antenna

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What is the primary use of a Beverage antenna?
  • Correct Answer
    Directional receiving for low HF bands
  • Directional transmitting for low HF bands
  • Portable direction finding at higher HF frequencies
  • Portable direction finding at lower HF frequencies

An application for a Beverage antenna is directional receiving for low HF bands.


The Beverage antenna is not effective for transmitting but is a highly effective and relatively inexpensive antenna for the directional reception of radio signals. Its effectiveness is greatest for the lower frequency HF bands (7 MHz and lower).

It's not very portable due to its size.

Wikipedia: Beverage antenna QSL: Beverage antenna

Think Dr. Pepper is a beverage. "D"irectional "R"eceiving Helpful Hint: You Receive a Beverage

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In which direction or directions does an electrically small loop (less than 1/3 wavelength in circumference) have nulls in its radiation pattern?
  • In the plane of the loop
  • Correct Answer
    Broadside to the loop
  • Broadside and in the plane of the loop
  • Electrically small loops are omnidirectional

Without going into antenna design, you might remember this by looking at the broadside of a loop - it would look like a zero. So, think of zero radiation in that direction as a "null."

Hint: The correct answer contains the word "broadside". However there are two answers that use that word, so just remember the question asks us about a "small" loop and choose the "smaller" (shorter) answer with the word broadside in it.

Ref tutorialspoint: Antenna Theory - Loop


Broadside to the loop means perpendicular to the plane of the loop. When the loop is small in relation to the wavelength, it radiates along the plane of the loop, and the nulls are perpendicular to the plane of the loop.

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Which of the following is a disadvantage of multiband antennas?
  • They present low impedance on all design frequencies
  • They must be used with an antenna tuner
  • They must be fed with open wire line
  • Correct Answer
    They have poor harmonic rejection

Since multiband antennas are designed to be resonant at many different frequencies, they are much less resistant to signals that come in on harmonics of the frequencies for which they are tuned. This can result in interference from harmonics that may not affect a single band antenna.

Stupid hint: The battle of the bands had a poor harmonica player.

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What is the common name of a dipole with a single central support?
  • Correct Answer
    Inverted V
  • Inverted L
  • Sloper
  • Lazy H

Inverted V (or Vee) antenna, can be both center and off-center fed.

Wikipedia: Inverted vee antenna

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What is the combined vertical and horizontal polarization pattern of a multi-wavelength, horizontal loop antenna?
  • A figure-eight, similar to a dipole
  • Four major loops with deep nulls
  • Correct Answer
    Virtually omnidirectional with a lower peak vertical radiation angle than a dipole
  • Radiation maximum is straight up

This question was deleted from the 2023-2027 questions pool.

A dipole antenna mounted sufficiently above ground will exhibit a radiation pattern that’s roughly toroidal (big, fat donut), oriented co-axial with the antenna, near the resonant frequency, resulting in a radiation polarization as much vertically as horizontally.

A horizontally oriented loop antenna exhibits a radiation pattern that resembles that of a dipole that has been bent into a curve so that the toroidal pattern is still oriented co-axial to the loop but now extends around the entire loop, resulting in a combined radiation pattern outward (horizontal) omnidirectional polarization and an upward (vertical) polarization. Furthermore, as a result of the extended toroidal pattern, the relative peak vertical signal strength is lower than that of a dipole, because the extra signal strength is diverted horizontally.

Hint: 'vertical' in both Q and A

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