 All RF Cafe Quizzes make great fodder for
employment interviews for technicians or engineers - particularly those who are
fresh out of school or are relatively new to the work world. Come to think of it,
they would make equally excellent study material for the same persons who are going
to be interviewed for a job. Bonne chance, Viel Glück, がんばろう,
buena suerte, удачи, in bocca al lupo, 행운을 빕니다,
ádh mór, בהצלחה, lykke til, 祝你好運.
Well, you know what I mean: Good luck!
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RF Cafe Quizzes.
Note: Some material based on books have quoted passages.
Return to RF Cafe Quiz #9
1. Where did Bluetooth™ get its name?
b) In honor of Harald
Blåtand, once king of Denmark.
Bluetooth was named by Ericsson (inventor of BT) after Danish King, Harald Blåtand
(Bluetooth in English), who lived in the latter part of the 10th century. According
to lore, he ate so many blueberries that his teeth turned blue (no kidding).
2. Where did
ZigBee
get its name?
b) From the zigzag path of a bee
According to authorities on the matter, the system was so named
because it allowed networked devices to swarm around each other
and stay connected, like worker bees around a hive.
3. Who is credited with conceiving of spread spectrum radio communications?
c) Actress Hedy Lamarr
1930s actress Hedy Lamarr, “The Mother of Spread Spectrum,” is widely credited
with having introduced the concept of spread spectrum radio communications as an
application for thwarting jamming on guided torpedoes during WWII. The work of
Lamarr's (and her piano instructor George Antheil) culminated
in U.S. Patent 2,292,387, “Secret Communication System,” granted on August 11, 1942.
Those were the days when Hollywood stars were patriotic and heroic, rather than
being the cowardly traitors of today.
4. What is meant by the front-to-back ratio of a
Yagi antenna?
c) Power radiated in the front main lobe vs. power in opposite direction
The series of driven (radiator) and reflector (director) elements in the Yagi
design produce a radiation pattern that is concentrated in one direction (directivity).
5. In an FM modulator with a 10 kHz deviation and a 5 kHz maximum modulating
frequency, what is the total occupied bandwidth?
d) 30 kHz
The maximum excursion on either side of carrier frequency (both above and below)
is the sum of the deviation and the modulating frequency (10 kHz + 5 kHz = 15 kHz),
so, total occupied bandwidth is twice that amount (lower + upper) of 30 kHz.
6. Which WLAN standard provides the highest data rate?
d) IEEE802.11n (2.4 GHz RF)
The spec data throughputs are as follows: 802.11a = 54 Mbits/s, 802.11b = 11
Mbits/s, 802.11g = 54 Mbits/s, 802.11n = 100+ Mbits/s (Pre-n systems delivering
this rate, but yet-to-be-finalized spec calls for up to 600 Mbits/s).
7. Why might the mounting orientation of a surface mount capacitor affect frequency
response?
a) The plates in the body could be either parallel to or perpendicular to the
PCB, affecting coupling
Most surface mount capacitors are of multi-layer construction with alternating
conductive plates and insulating (dielectric) layers. Edge fringing effects and
the proximity to adjacent components (including the substrate) will affect the effective
capacitance depending on whether the plates happen to be mounted parallel to or
perpendicular to the those components.
8. If you were handed an unprocessed wafer of gallium arsenide (GaAs), silicon
(Si), silicon-germanium (SiGe), and gallium nitride (GaN), how would you know which
is GaN?
a) GaN is transparent and the others are not
The wide band gap energy of GaN renders it transparent to visible light – it
looks like glass. The other wafers are all very dark in color.
9. The Smith Chart plot of a 50 ohm cable (in a 50 ohm system) spirals inward
as the impedance is plotted through multiple cycles. What is that indicative of?
a) A lossy cable
Attenuation in the cable increases the resistive component of the cable as the
length increases.
10. What are the three primary JEDEC models used for ESD testing?
c) Human Body (HBM), Machine (MM), and Charged Device (CDM) Model
JEDEC (Joint Electron Device
Engineering Council) specifies the Human Body Model in EIA/JESD22-A114-x (electrically
simulates the discharge RC network of the human body), the Machine Model in EIA/JESD22-A115-x
(the discharge path of a grounded machine), and the Charged Device Model in EIA/JESD22-C101-x
(the discharge path of device isolated by its package).
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