Tells Flashcards
What is Bandwidth ?
Its a range of freq within a frequency spectrum.
Perfect square wave:
BW = 1/2d Or 1/T
NON Square wave:
BW = 1/d
Whats the Freq ranges for the following?
HF.
VHF.
UHF.
SHF.
HF. 3-30Mhz
VHF. 30-300Mhz
UHF. 300-3Ghz
SHF. 3-30Ghz
In the time domain…
By only increasing or reducing the pulse duration (d), will have what effect on the frequency domain….?
Increasing (d)
- Will reduce your lobe width/bandwidth
Reducing (d)
- Will increase your lobe width/bandwidth
In the freq domain…
By only increasing or reducing the Lobe width (1/d), will have what effect on the time domain….?
Increasing (1/d) - (higher range of freq)
- Will reduce your pulse width
Reducing (1/d) - (lower range of freq)
- Will increase your pulse width
In the time domain..
By only increase or reducing the time period (T), will have what effect on the frequency domain….?
Increasing (T)
- Reduces PRF (1/T)
- Allowing for more spectral lines/ Harmonics to be present within the lobe
Reducing (T)
- Increasing PRF(1/T)
- Allowing for less spectral lines/ Harmonics to be present within the lobe
The frequency domain…
By only increasing or reducing the PRF (1/T), will have what effect on the time domain….?
Increasing PRF:
- Reduce the time period (T)
Reducing PRF:
- Increase the time period (T)
What is the PRF
Pulse repetition frequency
1/T
What is the formula for S/N ratio in dB for Voltage?
20Log10(Vsignal/Vnoise)
What is the formula for S/N ratio in dB for Power?
10Log10(Psignal/Pnoise)
What is termed as a complex Waveform?
Any wave that consists of more than 2 Sine waves
What is the relationship between Bandwidth and Bitrate?
Bitrate = 2 x Bandwidth
OR
Bandwidth = Bitrate / 2
What does a perfect SQUARE wave consist of?
The fundamental frequency and all the odd harmonics
Duty cycle = 50% or 1/2 or 0.5
1/T ,1/d, 3/T ,2/d, 5/T
What makes up a NON-Perfect SQUARE wave?
The fundamental frequency and all the odd and even harmonics
Duty cycle = 33% or 1/3 or 0.33
1/T , 2/T ,1/d, 4/T , 5/T ,2/d
Name 3 Electrical Characteristics of a Wire/Link ?
- Resistance
- Inductance
- Capacitance
What is the formula for your Duty cycle?
Duty cycle = d/T
What do we know about the relationship between MARK SPACE ratio and the Duty cycle if
Mark space ratio is 1:4
Means the Duty cycle is 1:5
What is a signal prone to, when traveling through a link?
- Distortion
- Attenuation
- Niose
S/N difference for comms links
Fibre optics
Attenuation?
Electrical noise pickup?
S/N?
Attenuation:
- Very low
Electrical noise pickup:
- None
S/N:
- Excellent
S/N difference for comms links
twisted pair/coax
Attenuation?
Electrical noise pickup?
S/N?
Attenuation:
- Moderate
Electrical noise pickup:
- Low
S/N:
- Good
S/N difference for comms links
wireless
Attenuation?
Electrical noise pickup?
S/N?
Attenuation:
- Severe over long ranges
Electrical noise pickup:
- No screening
S/N:
- Worst case
Characteristics of a good communications system
Transmitter requirements?
Power
Modulation
Bandwidth
Characteristics of a good communications system
Receiver requirements?
Selectivity (selecting wanted signals)
Sensitivity (good S/N ratio)
Bandwidth
Advantages of using digital signals compared to analogue
Error correction
Remove noise
Encryption
Name a few error correction techniques?
Parity bit
Hamming code