#1: Signals & Systems

Question 1

What is the frequency of light + its velocity in a vacuum?

Answer 1

frequency = 10^15 Hz velocity = 3x10^8 m/s

Question 2

Velocity = ______ x wavelength

Answer 2

frequency

Question 3

Wavelength = _____ / frequency

Answer 3

velocity

Question 4

UHF = ____ High Frequency = 300_Hz - 3__Hz What sort of devices use this frequency spectrum?

Answer 4

Ultra (High Frequency) 300MHz - 3GHz Wireless LANs, modern TVs, high end 2-way radios, mobile phones

Question 5

What frequency band + spectrum is FM radio?

Answer 5

VHF (Very High Frequency) 30 - 300MHz

Question 6

Define a ‘signal’.

Answer 6

An amplitude that varies with time

Question 7

Express radians in terms of frequency

Answer 7

w = 2*pi*f

Question 8

Frequency is the ____ of _____.

Answer 8

Rate ; change

Question 9

What is a radio signal (in terms of actual energy reaching its destination?)

Answer 9

Electromagnetic waves travelling through air or free space - cables not required!

Question 10

Describe the steps in calculating the RMS value of a signal

Answer 10

1) square the signal 2) find the average of the area under the signal (e.g. integrate over a period) 3) square-root this answer (undo step 1)

Question 11

What would the RMS of x(t) equal?

Answer 11

x(t) / sqrt(2)

Question 12

What is a decibel, and what is it used for?

Answer 12

A tenth of a bell.

It illustrates the power of a signal or gain of a system via a logarithmic scale.

Question 13

Why do we use a logarithmic scale?

Answer 13

Human hearing is based off a logarithmic scale.

Big numbers are easier to deal with on a log scale.

Question 14

Any resistive component above 0°C emits ____ ____.

Answer 14

thermal noise

Question 15

Using log rules, re-write:

y = log_b x

Answer 15

b^y = x

Question 16

What is ‘SNR’, and what is its use?

Answer 16

Signal to Noise Ratio.

Noise is only useful when comparing it to the signal strength to measure the actual distortion.

Question 17

State Fouriers Theorem.

Answer 17

A continuous periodic function may be expressed as…

…the sum of a series of sine or cosine terms…

…each of which has specific amplitude and phase coefficients known as ‘Fourier coefficients’.

Question 18

What does ‘THD’ stand for, and what does it mean?

Answer 18

Total Harmonic Distortion is the measurement of all harmonic components present in a signal.

Question 19

What does ‘dBm’ mean?

Answer 19

decibell-miliwatts

Indicates a logarithmic expresison with reference to 1 miliwatt

Question 20

Convert ‘0dBm’ to mW.

Answer 20

0 = 10 log10 PmW

PmW = 100/10

PmW = 1mW

Question 21

What’s the difference between a higher and lower ordered filter?

Answer 21

A higher ordered filter has a sharper response curve, but is more expensive.