1.3 Transmission Limitations

Question 1

What is attenuation?

Answer 1

Decrease in signal strength as a functino of distance the signal travels over a transmission medium.

Occurs due to field interactions.

Question 2

What factors affect attenuation?

Answer 2

Frequency and medium

Question 3

What is the attenuation coefficient alpha?

Answer 3

Relationship between loss and distance travelled in the medium.

Question 4

Answer 4

34W

Question 5

What is Delay Distortion?

Answer 5

Occurs when the propagation delay is not constant over the frequency range of the signal. Signals with different frequency components will be distorted because not all frequencies are delayed by the same amount.

Question 6

What 2 factors will increase Delay Distortion?

Answer 6

Bandwidth - wider range of freq’s, more difference in delay

Long distances - more delay

Question 7

What is Noise?

Answer 7

Unpredictable and unwanted signals that are added to the transmitted signal.

Question 8

What are the two main types of Noise?

Answer 8

Thermal Noise
Impulse Noise

Question 9

What is Thermal Noise?

Answer 9

Due to thermal disturbance of electrons in a conductor.

Question 10

What is Impulse Noise?

Answer 10

Irregular pulses caused by natural phenomena such as electrical storms and sun activity.

Question 11

What is the biggest limiting factor in all communication systems?

Answer 11

Noise because it cannot be removed completely.

However, you could argue it is bandwidth because BW will impact the amount of noise and it is hard to find channels to transmit on because the airways are crowded.

Question 12

What is the Equivalent Noise Temperature?

Answer 12

It is all the white noise combined with the Thermal Noise.

Question 13

What is Interference?

Answer 13

Structured, man-made signals.

Question 14

Does bandwidth alone dictate maximum channel capacity?

Answer 14

No? Noise limits our data rate without needing to increase bandwidth.

Question 15

Bit Rate vs. Baud Rate

Answer 15

Bit Rate: the number of bits that are transmitted over a communication link in 1 second.

Baud Rate: the number of symbols which can be transmitted over a communication line in 1 second. A symbol can represent multiple bits.

Question 16

What does teh Hartley Shannon Law tell us?

Answer 16

The maximum channel capacity for a finite-bandwidth channel subject to Additive White Gaussian Noise (AWGN).

Question 17

What would the channel capacity be if there was no noise?

Answer 17

By shannon hartley law, the SNR would tend to infinity so the capacity would also tend to infinity.

Question 18

What is a Standing Wave in a transmission line? Why is it undesirable?

Answer 18

When the impedence of the line does not match the impedence of the load, some power is reflected back towards the source.

It is inefficient and the return constructively interferes and may damage components.

Question 19

What is the Reflection Coefficient? (TDR)

Answer 19

The ratio of the amplitudes of the incident and reflected waves.

Question 20

What is the reflection coefficient for a short circuit?

Open circuit?

Perfectly matched?

Answer 20

Short circuit: -1

Open circuit: 1

Matched: 0

Question 21

What is the Voltage Standing Wave Ratio?

Answer 21

A measure of the maximum and minimum amplitudes along the transmission line.

Question 22

What is Time Domain Reflectometry?

Answer 22

Sending a pulse down the line nd analyzing the time of reflected signals to determine impedance variations and the distance to faults.