First Midterm Exam

### Prof. M. S. Al Salameh

Solve clearly the following three problems.    Time allowed: 45 minutes.

A communication link has the following parameters:

Transmitter: tower height = 20 m, antenna gain = 10 dB, and power = 300 W.

Receiver: tower height = 50 m, antenna effective area = 5 m2

Distance between transmitter and receiver = 10 km, and frequency of operation = 345 MHz.

Determine the:

a)                  propagation zone of the receiving antenna

b)                  equivalent free-space range

Consider a 2 MHz broadcasting system. Assume that the earth has conductivity of 10-2 S/m and dielectric constant of 15. If the signal level at a receiver is 54 dB below it’s free space value. Find the:

a)                  attenuation factor of the wave

b)                  distance between the transmitter and receiver. Check for flat earth or spherical earth.

The maximum usable frequency at a broadcasting station is 10 MHz. The wave is expected to be reflected at a height of 250 km where the electron concentration is 1011 m-3. Find the:

a)                  elevation angle, beyond which the wave escapes from the ionosphere.

b)                  corresponding skip distance.

SECOND MIDTERM EXAM

Winter 2009

Prof. M. S. Al salameh

Prob. 1: (13 points)

A 550 ml of water starts to boil in a microwave oven after 3 minutes. Note that for water 1 ml=1 gm. The microwave oven power is 1000 W, and the heat of evaporation of water is 2500 J/ml. The specific heat of water is 4.186055 J/(gm °C). The water has conductivity of 4 S/m. Estimate the

a)      Initial temperature of water before microwave heating,

b)      electric field within the water,

c)      energy absorbed by 1 ml of water

Prob. 2: (12 points)

Measurements of the path loss L in the city of Irbid vs. the distance d between transmitter and receiver are shown in the table below.

 L (dB) d (km) -102 0.6 -129 2 -149.5 5 -160 8

This communication system has frequency of 1800 MHz, transmitting antenna gain of 12, and transmitter power of 3.9 W.

a)      Find the exponent of the power law with distance,

b)      If the electric field at the receiver is 1mV/m, calculate the distance between the transmitter and receiver.

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Jordan University of Science & Technology

Winter 2009              Prof. Mohammed S. Al Salameh

In your solution, suitable unit should be written for each quantity.

Prob. 1: (15 points) [Not in EE407]

A 1.8 GHz fixed-site transmitter with call success rate of 85% delivers an average 40 dBmV/m at the street level in the edge of an urban coverage area with sR =4 dB, sLN =3 dB, sveg =5 dB, building loss LB= 6 dB, Lveg= 3 dB, sB =3 dB. Compute the:

(a)   Total standard deviation,

(b)  Total losses,

(c)   z value,

(d)  Signal margin,

Use this table:

 z 0 0.253 0.524 0.842 1.282 1.645 2.326 CSR 0.5 0.6 0.7 0.8 0.9 0.95 0.99

Prob. 2: (15 points)

For the communication system shown below at ambient temperature of 30 °C, find:

(a)   (3 points)

Received power at the receiving antenna,

(b)  (6 points)

Equivalent system temperature,

(c)   (3 points)

Receiver output noise power referred to antenna,

(d)  (3 points) Prob. 3: (10 points)

Human eyeball has the following electrical properties: er=70, s=2 S/m, r=1015 kg/m3 at frequency of 450 MHz. Eyeball mass is 8 g, and specific heat c=5 J/(g °C). After handheld transceiver conversation of 40 minutes, temperature rise in the eye was 3 °C. Neglecting other thermal gain and loss mechanisms, compute the following quantities in the eye:

(a)   (3 points)

Specific absorption rate,

(b)  (4 points)

Electric field,

(c)   (3 points)

Energy absorbed.