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| 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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