1.3 Transmission Limitations Flashcards
What is attenuation?
Decrease in signal strength as a functino of distance the signal travels over a transmission medium.
Occurs due to field interactions.
What factors affect attenuation?
Frequency and medium
What is the attenuation coefficient alpha?
Relationship between loss and distance travelled in the medium.
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What is Delay Distortion?
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.
What 2 factors will increase Delay Distortion?
Bandwidth - wider range of freq’s, more difference in delay
Long distances - more delay
What is Noise?
Unpredictable and unwanted signals that are added to the transmitted signal.
What are the two main types of Noise?
Thermal Noise
Impulse Noise
What is Thermal Noise?
Due to thermal disturbance of electrons in a conductor.
What is Impulse Noise?
Irregular pulses caused by natural phenomena such as electrical storms and sun activity.
What is the biggest limiting factor in all communication systems?
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.
What is the Equivalent Noise Temperature?
It is all the white noise combined with the Thermal Noise.
What is Interference?
Structured, man-made signals.
Does bandwidth alone dictate maximum channel capacity?
No? Noise limits our data rate without needing to increase bandwidth.
Bit Rate vs. Baud Rate
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.
What does teh Hartley Shannon Law tell us?
The maximum channel capacity for a finite-bandwidth channel subject to Additive White Gaussian Noise (AWGN).
What would the channel capacity be if there was no noise?
By shannon hartley law, the SNR would tend to infinity so the capacity would also tend to infinity.
What is a Standing Wave in a transmission line? Why is it undesirable?
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.
What is the Reflection Coefficient? (TDR)
The ratio of the amplitudes of the incident and reflected waves.
What is the reflection coefficient for a short circuit?
Open circuit?
Perfectly matched?
Short circuit: -1
Open circuit: 1
Matched: 0
What is the Voltage Standing Wave Ratio?
A measure of the maximum and minimum amplitudes along the transmission line.
What is Time Domain Reflectometry?
Sending a pulse down the line nd analyzing the time of reflected signals to determine impedance variations and the distance to faults.
