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#9
 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.
Click here for the complete list of
RF Cafe Quizzes.
Note: Some material based on books have quoted passages.
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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