est question for iecep 2012

QUESTION:A communications engineer at IBM Zuerich Research Laboratory who developed an encoding technique called Trellis Code Modulation (TCM), which combines encoding and modulation to reduce the probability of error.

ANSWER:Dr. Gottfried Ungerboeck

Reference: Electronics Communications Systems Wayne Tomasi, p. 391

QUESTION:Is a registered trademark of Varian Associates which is a hybrid combination of klystron driver and travelling wave tube output section in tandem in the same envelope.

ANSWER:Twystron

Reference: Electronic Communication System by Kenedy page 411

QUESTION:Cavity magnetron, like the klystron, causes electrons to bunch. This is an important effect known as ___________.

ANSWER:Phase-focussing effect

Reference: Electronic Communication System by Kenedy page 395

QUESTION:The WARC was a technical conference of the International Telecommunications Union (ITU) which provides satellite frequency assignments. WARC stands for ____________.

ANSWER:World Administrative Radio Conference


QUESTION:XMODEM is the first file transfer protocol designed to facilitate transferring data between two personal computers (PCs) over the public switched telephone network. It was developed in 1979 by a man named _________________.

ANSWER:Ward Christiansen


QUESTION:___________ is a wireless networking scheme that competes with both 802.11 and bluethooth schemes. It uses frequency hopping and spread spectrum communication at 2.4GHz and is intended for small home networks.

ANSWER:HomeRF

Reference: Electronics Communications Systems Roy Blake, p. 870

QUESTION:Determine the fade margin for the following conditions: Distance between sites, D=50km; Frequency, f=1.8GHz; very dry mountainous terrain and a reliability of 99.9999%

ANSWER:36.25db

SOLUTION:Fm = 30logD + 10log(6ABf) – 10log9=(1-R) – 70

where: D - distance in kilometre A - roughness factor

0.25 for mountainous terrain B – factor to convert a worst-month probability to an annual probability

0.125 for very dry mountainous terrain R – reliability expressed in decimal F – frequency in Gigahertz

Fm = 30log(50) + 10log(6x0.25x0.125x1.8) – 10log9=(1-.999999) – 70Fm = 36.25dB

Reference: Electronics Communications Systems Wayne Tomasi, p. 628-629

QUESTION:A fiber is rated as having a bandwidth-distance product of 500kHz-km. Find the rise time of a pulse in a 5km length of this cable.

ANSWER:5000ns

SOLUTION:D = 500/Bl

Where D – pulse spreading constant in ns/km Bl – Bandwidth-distance product in Mhz-km

D = 500/(0.500Mhz)D = 1000ns/Km

TRT = D x lWhere I = length of the cable

TRT = 1000ns/km x 5kmTRT = 5000ns

Reference: Electronics Communications Systems Roy Blake, p. 924

QUESTION:For a 2m diameter parabolic reflector with 10W of power radiated by the feed mechanism operating at 6GHz with a transmit antenna efficiency of 55% and an aperture efficiency of 45%, determing the receive power gain.

ANSWER:39.4dB

SOLUTION:ƛ = c / f

where c – speed of light (m/s)f – frequency of operation (Hz)

ƛ = 3x108m/s / 6x109 Hzƛ = 0.05meters

AP = 10 log ( 5.4 (D/ƛ)2 )Where D – Dish diameter in meters

ƛ – wavelength in meters per cycleAP = 10 log ( 5.4 (2/0.05)2 )Ap = 39.4 dB


QUESTION:Calculate the minimum receivable signal in a radar receiver which has an IF bandwidth of 1.5MHz and a 9-dB noise figure.

ANSWER:4.17x10-14 W

SOLUTION:NF = antilog (9/10)NF = 7.943

PMIN = KTOBW (NF – 1)Where K – Boltzmann’s Constant

TO – Ambient Temperature BW – Bandwidth NF – Noise Figure in decimal

PMIN = 1.38x1023 x 290 x 1.5x106 (7.493 – 1)PMIN = 4.17x10-14 W

Reference: Electronics Communications Systems George Kennedy, p. 610

est question for iecep 2012

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