Fichas
OVERALL TEST
Fichas del conjunto (76)
- 1Purpose of a receiver?To convert EM energy into usable energy
- 23 Requirements of an effective receiver?Select the wanted signal
Extract the intelligence
Produce an output of sufficient power - 34 Receiver characteristics?Sensitivity
Selectivity
Stability
Noise - 4Expand and define RF?Radio Frequency
(The carrier, raw state, no information) - 5Expand and define AF?Audio Frequency
Frequency audible to the average human ear - 6Expand and define IF?Intermediate Frequency
RF is shifted to to produce an AF - 7What is heterodyning?Two frequencies are mixed and multiplied to create two new frequencies
- 85 Types of filter?High pass
Low pass
Band pass
Notch
Band reject - 9How do you work out Rx bandwidth?Higher frequency level - lower frequency level
- 10Define squelch?Used to suppress the audio of a receiver in the absence of a sufficiently strong and desired input signal
- 11Define modulation?The process where information is superimposed upon the RF (Carrier wave)
- 12What is the modulating wave?The waveform of the original intelligence
- 13What is the carrier wave?The wave that is used to carry the modulating wave
(To gain further distance) - 14What is the modulated wave?The waveform that is transmitted
- 15What is AM?(Amplitude modulation)
Method in which the amplitude of the modulated wave is varied in accordance with the amplitude of the modulating wave. - 16If the amplitude of the transmission stays the same it is said to have a..... envelope?Constant
- 17If the amplitude of the transmission varies in a repetitive manner it is said to have a...... envelope?Periodic
- 18How would you work out AM transmission bandwidth?2 x modulating frequency
- 19How would you work out depth of modulation?Peak AF voltage/ Peak RF voltage
Answer X 100 = %
(80% is best) - 20What is the result from a modulation value of over 100%?Distortion
- 21What is a double sideband?The method of operation where both side bands of frequencies are transmitted equally.
- 22Speech frequency range is?300Hertz - 3400Hertz
- 23Describe an erect sideband?The higher the RF, the higher the AF.
- 24Describe an inverted sideband?The lower the RF, the higher the AF.
- 253 DSB disadvantages?1- Waste of transmitter power
2- Excessive bandwidth
3- Prone to selective fading - 26What is a single sideband?Where only the upper or lower sideband is transmitted, and one sideband is completely attenuated.
- 272 Disadvantages of SSB?Carrier needs to be re-inserted
SSB equipment must be stable - 28What is FM?The frequency of the carrier wave is varied in accordance with the amplitude of the modulating wave.
- 29Define centre frequency?The frequency occupied by the carrier when in an un-modulated state.
- 30Define frequency deviation?The amount of change in frequency from the centre frequency.
- 31What is carrier/frequency swing?The difference between the highest and lowest frequencies the modulated wave can attain.
- 32What is the deivation ratio?The ratio of the maximum frequency deviation and the highest permissible modulating frequency.
- 33What is the modulation index?The decimal number representing the ratio of the frequency deviation and the highest frequency of the modulating wave.
- 34How would you work out FM bandwidth?Carsons bandwidth.
2x (fd+fm) - 35Expand and define FSK?Frequency shift keying
RF carrier if shifted between two or more discreet frequency values. - 36Define shift?Difference between adjacent frequency levels.
- 37Define Excursion?Difference between the highest and lowest frequency levels
- 38How would you work out FSK bandwidth?Carsons bandwidth
Shift(Excursion) + bauds - 39Expand 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. - 40Define telegraphic structure?The arrangement and polarity of elements.
- 41Define element?A function of time, its polarity may be mark or space.
(1's and 0's) - 42Define mark and space?Mark = Voltage high/ binary 1
Space = Voltage low/ binary 0 - 43What is a baud?A unit of telegraphic speed (Number of elements per second)
- 44Expand and explain ETD?Element time duration
Time taken for one element to be transmitted.
(Expressed in Bauds, (B) ) - 45How is ETD calculated?1000/Bauds
- 46Expand and explain the FKFFundamental keying frequency
same as modulating frequency - 47How is the FKF calculated?Bauds/2 = Hertz
- 48How is OOK Tx BW calculated?5 x Bauds
- 49How is OOK Rx BW calculated?3 x Bauds
- 50Expand and explain MFSK?Multi level frequency shift keying
Number of levels and states the signal can change to is increased. - 512 Advantages of MFSK signalling?- Higher information rate
- Variable information rate - 522 Disadvantages of MFSK signalling?- Susceptible to drift due to narrow spacing
- More Rx and Tx processing needed - 53What is the data rate?The number of bits received as data by the receiving equipment
(Quoted in bps) (Bits per second) - 54Expand and explain MSK?Minimum shift keying
FSK transmission that has a baud speed of exactly twice the value of the shift. - 55Expand and explain MFC?Multiple frequency coding
Method of FSK where each frequency level represents partial or whole characters. - 56How many levels can be common in MFC and why?36, one per alphabet letter =26
one per number 0-9 = 10
26+10=36 - 57Common MFCs?11 MFC
7 MFC - 58How can an MFC be recognised?Sounds slow
Not in binary - 59Expand and explain PM?Phase modulation.
The phase of the carrier in changed in accordance with the amplitude of the modulating wave. - 60What is phase deviation?The amount of phase change produced by the modulating wave.
- 61Expand and explain PSK?Phase shift keying.
The carrier phase is shifted between discreet phase values. - 62The drop from the major lobe to the minor lobe in PSK = ?13.7dB
- 63The drop from the major lobe to the minor lobe in MSK = ?23.7dB
- 64What is an initial phase reference?Used to counter initial phase problems
- 65Expand and explain DPSK?Differential Phase shift keying
'Changes on a 1' - 66Explain abolute PSK?'Changes on a change'
(1-0 OR 0-1) - 67What 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.
- 68Expand and explain BPSK?Bi-Phase shift keying
Carrier is shifted between two discreet phase values. - 69Expand and explain QPSK?Quadrature- Phase shift keying
Carrier is shifted between four discreet phase values.
(Di-bits) - 70Explain Eight PSK?8PSK
Carrier is shifted between 8 discreet phase values.
(Tri-bits) - 71Expand and explain QAM?Quadrature amplitude modulation.
- 72Define amplitude ring?An imaginary circle that denotes the clusters that share a common amplitude.
- 73Define signal states?The total number of amplitude and phase combinations a signal can attain.
- 74Define phase states?Data is represented by the phase of the signal in relation to a reference.
- 75Explain the V.29 modem8 Phase states
4 Amplitude levels
16 signal states - 762 Benefits of QAM?1- High data rate
2- Improved adaptability
Información
- Descripción
- Fichas sobre OVERALL TEST, creado por B L el 26/02/2017.
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- B L
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