Flashcards by B L, updated more than 1 year ago
Created by B L almost 3 years ago


Flashcards on OVERALL TEST, created by B L on 02/26/2017.

Resource summary

Question Answer
Purpose of a receiver? To convert EM energy into usable energy
3 Requirements of an effective receiver? Select the wanted signal Extract the intelligence Produce an output of sufficient power
4 Receiver characteristics? Sensitivity Selectivity Stability Noise
Expand and define RF? Radio Frequency (The carrier, raw state, no information)
Expand and define AF? Audio Frequency Frequency audible to the average human ear
Expand and define IF? Intermediate Frequency RF is shifted to to produce an AF
What is heterodyning? Two frequencies are mixed and multiplied to create two new frequencies
5 Types of filter? High pass Low pass Band pass Notch Band reject
How do you work out Rx bandwidth? Higher frequency level - lower frequency level
Define squelch? Used to suppress the audio of a receiver in the absence of a sufficiently strong and desired input signal
Define modulation? The process where information is superimposed upon the RF (Carrier wave)
What is the modulating wave? The waveform of the original intelligence
What is the carrier wave? The wave that is used to carry the modulating wave (To gain further distance)
What is the modulated wave? The waveform that is transmitted
What is AM? (Amplitude modulation) Method in which the amplitude of the modulated wave is varied in accordance with the amplitude of the modulating wave.
If the amplitude of the transmission stays the same it is said to have a..... envelope? Constant
If the amplitude of the transmission varies in a repetitive manner it is said to have a...... envelope? Periodic
How would you work out AM transmission bandwidth? 2 x modulating frequency
How would you work out depth of modulation? Peak AF voltage/ Peak RF voltage Answer X 100 = % (80% is best)
What is the result from a modulation value of over 100%? Distortion
What is a double sideband? The method of operation where both side bands of frequencies are transmitted equally.
Speech frequency range is? 300Hertz - 3400Hertz
Describe an erect sideband? The higher the RF, the higher the AF.
Describe an inverted sideband? The lower the RF, the higher the AF.
3 DSB disadvantages? 1- Waste of transmitter power 2- Excessive bandwidth 3- Prone to selective fading
What is a single sideband? Where only the upper or lower sideband is transmitted, and one sideband is completely attenuated.
2 Disadvantages of SSB? Carrier needs to be re-inserted SSB equipment must be stable
What is FM? The frequency of the carrier wave is varied in accordance with the amplitude of the modulating wave.
Define centre frequency? The frequency occupied by the carrier when in an un-modulated state.
Define frequency deviation? The amount of change in frequency from the centre frequency.
What is carrier/frequency swing? The difference between the highest and lowest frequencies the modulated wave can attain.
What is the deivation ratio? The ratio of the maximum frequency deviation and the highest permissible modulating frequency.
What is the modulation index? The decimal number representing the ratio of the frequency deviation and the highest frequency of the modulating wave.
How would you work out FM bandwidth? Carsons bandwidth. 2x (fd+fm)
Expand and define FSK? Frequency shift keying RF carrier if shifted between two or more discreet frequency values.
Define shift? Difference between adjacent frequency levels.
Define Excursion? Difference between the highest and lowest frequency levels
How would you work out FSK bandwidth? Carsons bandwidth Shift(Excursion) + bauds
Expand and define OOK? On-Off keying Simplest form of AM, a carrier is keyed on or off a voltage according to a pre-arranged code.
Define telegraphic structure? The arrangement and polarity of elements.
Define element? A function of time, its polarity may be mark or space. (1's and 0's)
Define mark and space? Mark = Voltage high/ binary 1 Space = Voltage low/ binary 0
What is a baud? A unit of telegraphic speed (Number of elements per second)
Expand and explain ETD? Element time duration Time taken for one element to be transmitted. (Expressed in Bauds, (B) )
How is ETD calculated? 1000/Bauds
Expand and explain the FKF Fundamental keying frequency same as modulating frequency
How is the FKF calculated? Bauds/2 = Hertz
How is OOK Tx BW calculated? 5 x Bauds
How is OOK Rx BW calculated? 3 x Bauds
Expand and explain MFSK? Multi level frequency shift keying Number of levels and states the signal can change to is increased.
2 Advantages of MFSK signalling? - Higher information rate - Variable information rate
2 Disadvantages of MFSK signalling? - Susceptible to drift due to narrow spacing - More Rx and Tx processing needed
What is the data rate? The number of bits received as data by the receiving equipment (Quoted in bps) (Bits per second)
Expand and explain MSK? Minimum shift keying FSK transmission that has a baud speed of exactly twice the value of the shift.
Expand and explain MFC? Multiple frequency coding Method of FSK where each frequency level represents partial or whole characters.
How many levels can be common in MFC and why? 36, one per alphabet letter =26 one per number 0-9 = 10 26+10=36
Common MFCs? 11 MFC 7 MFC
How can an MFC be recognised? Sounds slow Not in binary
Expand and explain PM? Phase modulation. The phase of the carrier in changed in accordance with the amplitude of the modulating wave.
What is phase deviation? The amount of phase change produced by the modulating wave.
Expand and explain PSK? Phase shift keying. The carrier phase is shifted between discreet phase values.
The drop from the major lobe to the minor lobe in PSK = ? 13.7dB
The drop from the major lobe to the minor lobe in MSK = ? 23.7dB
What is an initial phase reference? Used to counter initial phase problems
Expand and explain DPSK? Differential Phase shift keying 'Changes on a 1'
Explain abolute PSK? 'Changes on a change' (1-0 OR 0-1)
What is a polar plot? Diagram used to show which pases are being used and permits the operator to determine the quality of a demodulated signal.
Expand and explain BPSK? Bi-Phase shift keying Carrier is shifted between two discreet phase values.
Expand and explain QPSK? Quadrature- Phase shift keying Carrier is shifted between four discreet phase values. (Di-bits)
Explain Eight PSK? 8PSK Carrier is shifted between 8 discreet phase values. (Tri-bits)
Expand and explain QAM? Quadrature amplitude modulation.
Define amplitude ring? An imaginary circle that denotes the clusters that share a common amplitude.
Define signal states? The total number of amplitude and phase combinations a signal can attain.
Define phase states? Data is represented by the phase of the signal in relation to a reference.
Explain the V.29 modem 8 Phase states 4 Amplitude levels 16 signal states
2 Benefits of QAM? 1- High data rate 2- Improved adaptability
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