Questions
1 (a) Sketch a block diagram of a generic communications system and in your own words
explain what each of the blocks represent.
[10 Marks]
2 (a) Sketch a simple block diagram of a real communications system ensuring you label it
fully.
[10 Marks]
3 (a) Explain what following communication modes mean.
(i)
Simplex
(ii)
Half-Duplex
(iii)
Parallel
[10 Marks]
4 (a) Explain what following communication modes mean.
(i)
Broadcast
(ii)
Duplex
(iii)
Serial
[10 Marks]
5 (a) Explain the difference between serial transmission and parallel transmission using
diagrams if necessary. Give an advantage or disadvantage of each.
[10 Marks]
6 (a) Give two examples of where each of the following communications mediums may be
found.
(i)
Wireless
(ii)
Optical
(iii)
Copper
[10 Marks]
7 (a) Convert the following into
(i)
15000 kbits/s
(ii)
0.066 Mbits/s
(iii)
622 Mbits/s
(iv)
4000 bits/s
to
to
to
to
Mbits/s
kbits/s
Gbits/s
kbits/s
[10 Marks]
8 (a) Describe the difference between analogue and digital signals
[10 Marks]
Questions
9 (a) Give four advantages or disadvantages of a digital signal over an analogue signal.
[10 Marks]
10
(a) Describe Attenuation using diagrams if necessary.
[10 Marks]
11
(a) Convert the following
(i)
100mW into
1.
Watts
2.
µWatts
3.
nWatts
(ii)
1.
2.
3.
(iii)
1.
2.
3.
0.001 µW
pW
mW
nW
1795 x 10-8 W
µWatts
mW
Watts
[10 Marks]
12
(a) If a system has three cascaded amplifiers with gains of 12, 54, & 112 respectively.
What is their total gain? What is the individual gains in dB and their total gain in dB?
Verify you answer.
[10 Marks]
13
(a) If the input power into an amplifier is 0.5mW. What is this value in dBm?
[10 Marks]
14
(a) An amplifier has an output power of 12dBm. What is this value in mWatts?
[10 Marks]
15
(a) If an amplifier has an input power of 0.034mW and a gain of 768. What is its input
power in dBm, its gain in dB, its output power in dBm and its output power in Watts?
[10 Marks]
Questions
16
(a) If a system of amplifiers has an input power of –34dBm with gains of 8dB, 23dB and
6db respectively what is the output power in dBm? Prove you answer by converting
the values into mWatts.
[10 Marks]
17
(a) If an amplifier has an output power of 0dBm and a gain of 22dB what is its input
power in dBm and mWatts?
[10 Marks]
18
(a) If a system has an input power of 10dBm channel losses of -57db and amplifiers with
a total gain of 1374 what must the receiver minimum sensitivity be?
[10 Marks]
19
20
(a) A receiver with a sensitivity of -32dBm is at the end of a system of three amplifiers.
The two channels between the amplifiers have losses of 10dB each. If the input power
into the first amplifier is -16dBm what is the minimum gain of the 3 amplifiers if
they are equal?
[10 Marks]
(a)
Sketch 3 different types of network topology.
[10 Marks]
Solutions
1 (a)
Signal
Source
Transmitter
Channel
Receiver
Signal
Sink
The function of the transmitter is to take in an outside signal (from the signal source
e.g. mic, computer, cd player, magnetic tape) and convert it into a form appropriate to
the Channel and send it on to the medium (modulate the signal). The function of the
receiver is to take in the signal from the medium, if possible remove any noise or
distortion introduced by the transmitter and/or the medium and to convert it into a form
suitable for the signal sink (i.e. for a speaker, digital signal for a computer, signal to
power a motor).
[10 Marks]
2 (a)
E.g. Radio
Microphone
Radio Mast
Airwave
s
Aerial
Speaker
E.g. USB link
Memory
card
Electrical
Transmitter
Copper
wire
Electrical
Receiver
PC
[10 Marks]
6 (a) (i)
Wireless (radio and optical)
 Bluetooth
 Microwave telecommunications (public network)
 Wireless LAN
 Remote control
(ii)
Optical Fibre
 Telephone network
 Multimedia digital connections
 Plastic optical fibre in car networks
o Saab, BMW and Mercedes
 Local area networks
(iii)
Copper
 Telephone network
 PCB
Solutions


USB cable
Local area networks
[10 Marks]
20
(a)
end stations
NIC
NIC
NIC
Bus
NIC
NIC
NIC
NIC
end stations
repeater
repeater
repeater
Direction of
data flow
Ring
Ring
repeater
repeater
repeater
repeater
end stations
NIC
NIC
Star
NIC
NIC
NIC
NIC
NIC
end stations
[10 Marks]
1 (a)
[10 Marks]
1 (a)
[10 Marks]
1 (a)
[10 Marks]
Solutions
1 (a)
[10 Marks]
1 (a)
[10 Marks]
1 (a)
[10 Marks]