ARRL

News

Amateur Radio Quiz: The Yagi Antenna

03/02/2009

1) A parasitic element...
a. is connected to the feed line.
b. is not connected to the feed line.
c. must be parallel to the feed line.
d. is only for mechanical balance.

2) Directors are (longer) (shorter) than reflectors.

3) Directors are (longer) (shorter) than the driven element.

4) Second directors are (longer) (shorter) than the first directors.

5) A Yagi's driven element generally has a feedpoint impedance (lower) (higher) than 50 ohms.

6) Which of following is NOT a useful transmission-line impedance matching design to transform the Yagi driven-element impedance to 50 ohms for coax feed?
a. Strip-line
b. Gamma match
c. Beta match
d. Hairpin

7) "Plumber's Delight" construction means that all elements are...
a. made from threaded pipe.
b. not insulated from the boom.
c. at the same RF potential.
d. trapped.

8) A "driven cell" refers to...
a. a loop used as the driven element.
b. two or more driven elements.
c. more than one Yagi on a single mast.
d. extra-strong rotator hardware.

9) Reflectors have self-resonant frequencies (higher) (lower) than that of the driven element.

10) Adding parasitic elements is done to improve the antenna's...
a. front-to-back ratio.
b. forward gain.
c. both (a) and (b)
d. neither

11) The Yagi antenna was first described in...
a. 1926-28.
b. 1936.
c. 1946.
d. 1962.

12) The "2:1 Bandwidth" of a Yagi refers to the frequency range over which the antenna maintains a...
a. 2-to-1 SWR or less.
b. front-to-back ratio of at least 3 dB.
c. forward gain of at least 3 dB.
d. efficiency of 90 percent or greater.

13) A "quagi" is...
a. an array of four Yagis.
b. a Yagi with one or more quad-loop elements.
c. a quasi-Yagi design.
d. a lightweight Yagi.

14) "Tapered elements" are...
a. spaced closer together at one end of the antenna.
b. covered with insulating tape.
c. smaller in diameter at their tips than in their centers.
d. no longer in general use.

15) Increasing the number of elements in a Yagi (increases) (decreases) the antenna pattern beamwidth.

 

Bonus Question: Who was Dr Yagi's co-inventor of the antenna that is now only known by Yagi's name?

 

 

Answers:
1. b -- The currents in a parasitic element are created by the field from the driven element. No direct connection to the feed line is needed.
2. shorter
3. shorter
4. shorter
5. lower -- A typical Yagi's feedpoint impedance is in the neighborhood of 20 ohms.
6. a -- The gamma, beta, and hairpin (another name for the beta match) are all widely used to connect a 50 ohm feed line to a Yagi driven element.
7. b -- This type of construction allows all-metal mounting hardware, simplifying construction and placing all of the antenna at the same dc potential for grounding.
8. b -- Using multiple driven elements improves the feedpoint impedance stability over the designed frequency range.
9. lower
10. c -- Both gain and rejection of signals to the rear is improved by proper placement of parasitic elements.
11. a -- The antennas were described in the Japanese IEE journals in 1926 and 1927, while the English papers were published in the IRE journal in 1928.
12. a -- This is sometimes referred to as "SWR bandwidth."
13. b -- The broader frequency vs impedance characteristics of the loop help increase the SWR bandwidth of the antenna.
14. c -- Tapering reduces antenna weight and wind load.
15. decreases -- An antenna with more elements generally has a narrower or sharper radiation pattern.

Bonus - Dr Uda was the co-inventor of the "Yagi-Uda Array," known today by the simpler name.

H. Ward Silver, N0AX
Contributing Editor



Back