A Smorgasbord of RF Topics
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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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