# Wireless Standards KnowledgeAnswers to RF Cafe Quiz #21

All RF Cafe quizzes would make perfect fodder in 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.

Note: Some material based on books have quoted passages.

This quiz test your knowledge of the modern wireless bands.

1. What are the frequency bands for IEEE 802.11a and IEEE 802.11b/g, respectively?

d) IEEE 802.11a operates at 5.2 GHz (actually parts of 5.035 through 5.825 GHz), and IEEE 802.11b/g operates at 2.4 GHz (actually 2.412 through 2.484 GHz). Even though 'a' comes before 'b/g' and you might assume that means 802.11a would be the lower frequency, it is not. Both are in FCC Part 15 unlicensed bands.

2. Which wireless router type is most likely to use three antennas?

d) 802.11n. Theoretically, average uplink throughput rates when transmitting across 40 MHz channels (two, 20-MHz bonded channels, which the 802.11n standard allows) can be up to 40% greater in the 2x3 configuration than in the 2x2 configuration over distances of 30 to 40 feet and 20% greater in the 60- to 100-foot range.

3. On which frequency band does the EGSM mobile phone system operate?

b) 900 MHz. The full band is 880.0 - 915.0 MHz for the uplink, and 925.0 – 960.0 MHz for the downlink.

4. On which frequency band does the DCS/PCS mobile phone system operate?

a) 1800/1900 MHz. The full DCS (Digital Communication System) band is 1710–1785 MHz for the uplink and 1805–1880 MHz for the downlink. The full PCS (Personal Communication System) band is 1850-1910 MHz for the uplink and 1930–1990 MHz for the downlink.

5. On which frequency band does Bluetooth operate?

c) 2.4 GHz. Bluetooth operates within the license-free ISM band, just like 802.11b/g/n. Various countries favor specific parts of the band, but they all play together.

6. Which IEEE standard describes the Bluetooth system?

b) 802.15.1 to be exact. Bluetooth system was originally developed by Ericsson Mobile Platforms in Lund, Sweden. The name is an anglicized version of Old Norse Blátönn or Danish Blåtand, the name of the tenth-century king Harald I of Denmark and Norway ("Bluetooth").

7. Which type of modulation scheme does Bluetooth and WiFi employ?

d) Spread spectrum (SS). Bluetooth uses frequency hopping spread spectrum (FHSS), while WiFi uses direct sequence spread spectrum (DSSS).

8. Which of the following IEEE 802.x wireless systems currently offers the lowest data rate?

c) ZigBee is the simplest and lowest power consumption system in the 802.x family, and is governed by the IEEE 802.15.4 specification. Click on the thumbnail for a good overview.

9. What does NFC stand for?

c) Near Field Communications. NFC is an up-and-coming system that uses inductive or capacitive coupling between an active transceiver and an embedded 2-dimensional antenna for passing information across a short distance. Many cellphones are beginning to incorporate NFC for exchanging information between two devices' cases that are touching each other without actually making contact via a metal conductor.

10. Which of the following systems has been show to cause brain cancer, sterility, skin cancer, and in some cases sever burns  to the body?

d) All of the above. After collecting technical headlines on a daily basis for many years, I have discovered many articles which claim to have conclusively proven that all of the wireless technologies with transmit powers above a few milliwatts do cause one or more of the aforementioned maladies. Skins burns are caused not by the RF energy, however, but by Li-Po and Li-Ion  batteries catching on fire. BTW, there are as many studies that find no health risks as those that do (except for fiery batteries, which are always found to be harmful).
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