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G8 - SIGNALS AND EMISSIONS [2 exam questions - 2 groups]

G8 - SIGNALS AND EMISSIONS [2 exam questions - 2 groups]. G8A Carriers and modulation: AM; FM; single and double sideband ; modulation envelope; deviation; over modulation G8B Frequency mixing; multiplication; HF data communications; bandwidths of various modes. Amplitude Modulation.

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G8 - SIGNALS AND EMISSIONS [2 exam questions - 2 groups]

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  1. G8 - SIGNALS AND EMISSIONS [2 exam questions - 2 groups] • G8A Carriers and modulation: AM; FM; single and double sideband ; modulation envelope; deviation; over modulation • G8B Frequency mixing; multiplication; HF data communications; bandwidths of various modes Signals and Emissions

  2. Amplitude Modulation An unmodulated RF carrier wave A carrier wave amplitude modulated (AM) with a simple audio tone Signals and Emissions

  3. Amplitude Modulation An unmodulated RF carrier requires narrow bandwidth Modulation of the carrier creates sidebands. This requires more bandwidth. Transmitter power is spread across this bandwidth Signals and Emissions

  4. AM and SSB The carrier contains no audio information. The sidebands contain duplicate audio information By filtering out the carrier and one sideband, we save spectrum and concentrate our RF energy into a narrower bandwidth. SSB is therefore more efficient. Signals and Emissions

  5. G8A01 What is the name of the process that changes the envelope of an RF wave to convey information? • A. Phase modulation • B. Frequency modulation • C. Spread Spectrum modulation • D. Amplitude modulation Signals and Emissions

  6. G8A01 What is the name of the process that changes the envelope of an RF wave to convey information? • A. Phase modulation • B. Frequency modulation • C. Spread Spectrum modulation • D. Amplitude modulation Signals and Emissions

  7. G8A02 What is the name of the process that changes the phase angle of an RF wave to convey information? • A. Phase convolution • B. Phase modulation • C. Angle convolution • D. Radian Inversion Signals and Emissions

  8. G8A02 What is the name of the process that changes the phase angle of an RF wave to convey information? • A. Phase convolution • B. Phase modulation • C. Angle convolution • D. Radian Inversion Signals and Emissions

  9. Frequency Modulation Unmodulated carrier, full power at all times Waveform of modulating signal Modulated carrier with frequency deviation and constant amplitude “Over modulation” called “over deviation” on FM, causes the signal to become wider and potentially cause adjacent channel interference Signals and Emissions

  10. G8A03 What is the name of the process which changes the frequency of an RF wave to convey information? • A. Frequency convolution • B. Frequency transformation • C. Frequency conversion • D. Frequency modulation Signals and Emissions

  11. G8A03 What is the name of the process which changes the frequency of an RF wave to convey information? • A. Frequency convolution • B. Frequency transformation • C. Frequency conversion • D. Frequency modulation Signals and Emissions

  12. G8A04 What emission is produced by a reactance modulator connected to an RF power amplifier? • A. Multiplex modulation • B. Phase modulation • C. Amplitude modulation • D. Pulse modulation Signals and Emissions

  13. G8A04 What emission is produced by a reactance modulator connected to an RF power amplifier? • A. Multiplex modulation • B. Phase modulation • C. Amplitude modulation • D. Pulse modulation Signals and Emissions

  14. G8A05 What type of transmission varies the instantaneous power level of the RF signal to convey information? • A. Frequency shift keying • B. Pulse modulation • C. Frequency modulation • D. Amplitude modulation Signals and Emissions

  15. G8A05 What type of transmission varies the instantaneous power level of the RF signal to convey information? • A. Frequency shift keying • B. Pulse modulation • C. Frequency modulation • D. Amplitude modulation Signals and Emissions

  16. G8A06 What is one advantage of carrier suppression in a single-sideband phone transmission? • A. Audio fidelity is improved • B. Greater modulation percentage is obtainable with lower distortion • C. More transmitter power can be put into the remaining sideband • D. Simpler receiving equipment can be used Signals and Emissions

  17. G8A06 What is one advantage of carrier suppression in a single-sideband phone transmission? • C. More transmitter power can be put into the remaining sideband Signals and Emissions

  18. G8A07 Which of the following phone emissions uses the narrowest frequency bandwidth? • A. Single sideband • B. Double sideband • C. Phase modulation • D. Frequency modulation Signals and Emissions

  19. G8A07 Which of the following phone emissions uses the narrowest frequency bandwidth? • A. Single sideband • B. Double sideband • C. Phase modulation • D. Frequency modulation Signals and Emissions

  20. G8A08 What happens to the signal of an over-modulated single-sideband phone transmitter? • A. It becomes louder with no other effects • B. It occupies less bandwidth with poor high frequency response • C. It has higher fidelity and improved signal to noise ratio • D. It becomes distorted and occupies more bandwidth Signals and Emissions

  21. G8A08 What happens to the signal of an over-modulated single-sideband phone transmitter? • D. It becomes distorted and occupies more bandwidth Signals and Emissions

  22. G8A09 What control is typically adjusted for proper ALC setting on an amateur single sideband transceiver? • A. The RF Clipping Level • B. Audio or microphone gain • C. Antenna inductance or capacitance • D. Attenuator Level Signals and Emissions

  23. G8A09 What control is typically adjusted for proper ALC setting on an amateur single sideband transceiver? • B. Audio or microphone gain • Automatic Level Control (ALC) Signals and Emissions

  24. G8A10 What is meant by flat-topping of a single-sideband phone transmission? • A. Signal distortion caused by insufficient collector current • B. The transmitter's automatic level control is properly adjusted • C. Signal distortion caused by excessive drive • D. The transmitter's carrier is properly suppressed Signals and Emissions

  25. G8A10 What is meant by flat-topping of a single-sideband phone transmission? • Signal distortion caused by excessive drive Signals and Emissions

  26. G8A11 What happens to the RF carrier signal when a modulating audio signal is applied to an FM transmitter? • A. The carrier frequency changes proportionally to the instantaneous amplitude of the modulating signal • B. The carrier frequency changes proportionally to the amplitude and frequency of the modulating signal • C. The carrier amplitude changes proportionally to the instantaneous frequency of the modulating signal • D. The carrier phase changes proportionally to the instantaneous amplitude of the modulating signal Signals and Emissions

  27. G8A11 What happens to the RF carrier signal when a modulating audio signal is applied to an FM transmitter? • A. The carrier frequency changes proportionally to the instantaneous amplitude of the modulating signal Signals and Emissions

  28. G8A12 What signal(s) would be found at the output of a properly adjusted balanced modulator? • A. Both upper and lower sidebands • B. Either upper or lower sideband, but not both • C. Both upper and lower sidebands and the carrier • D. The modulating signal and the unmodulated carrier Signals and Emissions

  29. G8A12 What signal(s) would be found at the output of a properly adjusted balanced modulator? • A. Both upper and lower sidebands • A modulator in which the carrier and modulating signal are introduced in such a way that the output contains the two sidebands without the carrier. Signals and Emissions

  30. G8B01 What receiver stage combines a 14.250 MHz input signal with a 13.795 MHz oscillator signal to produce a 455 kHz intermediate frequency (IF) signal? • A. Mixer • B. BFO • C. VFO • D. Multiplier Signals and Emissions

  31. Heterodyne In radio and signal processing, heterodyning is the generation of new frequencies by mixing, or multiplying, two oscillating waveforms. It is useful for modulation and demodulation of signals, or placing information of interest into a useful frequency range. The two frequencies are mixed in a vacuum tube, transistor, diode, or other signal processing device. Mixing two frequencies creates two new frequencies, according to the properties of the sine function: one at the sum of the two frequencies mixed, and the other at their difference. These new frequencies are called heterodynes. Typically only one of the new frequencies is desired—the higher one after modulation and the lower one after demodulation. The other signal is filtered out of the output of the mixer. Signals and Emissions

  32. G8B01 What receiver stage combines a 14.250 MHz input signal with a 13.795 MHz oscillator signal to produce a 455 kHz intermediate frequency (IF) signal? • A. Mixer Signals and Emissions

  33. G8B02 If a receiver mixes a 13.800 MHz VFO with a 14.255 MHz received signal to produce a 455 kHz intermediate frequency (IF) signal, what type of interference will a 13.345 MHz signal produce in the receiver? • A. Local oscillator • B. Image response • C. Mixer interference • D. Intermediate interference 14255-13800 = 455 13800-13345 = 455 Signals and Emissions

  34. G8B02 If a receiver mixes a 13.800 MHz VFO with a 14.255 MHz received signal to produce a 455 kHz intermediate frequency (IF) signal, what type of interference will a 13.345 MHz signal produce in the receiver? • B. Image response 14255-13800 = 455 13800-13345 = 455 Signals and Emissions

  35. IMRRImage Response Rejection Ratio The ability of the receiver to reject this image gives the IMRR of the system. IMRR is measured in dB, giving the ratio of the wanted to the unwanted signal to yield the same output from the receiver. In a good design, ratios of >60 dB are achievable. Note that IMRR is not a measurement of the performance of the IF stages or IF filtering (selectivity) - the signal yields a perfectly valid IF frequency. Rather, it is the measure of the bandpass characteristics of the stages preceding the IF amplifier, which will consist of RF bandpass filters and usually an RF amplifier stage or two. Signals and Emissions

  36. G8B03 What stage in a transmitter would change a 5.3 MHz input signal to 14.3 MHz? • A. A mixer • B. A beat frequency oscillator • C. A frequency multiplier • D. A linear translator Signals and Emissions

  37. G8B03 What stage in a transmitter would change a 5.3 MHz input signal to 14.3 MHz? • A. A mixer Signals and Emissions

  38. G8B04 What is the name of the stage in a VHF FM transmitter that selects a harmonic of an HF signal to reach the desired operating frequency? • A. Mixer • B. Reactance modulator • C. Pre-emphasis network • D. Multiplier Signals and Emissions

  39. G8B04 What is the name of the stage in a VHF FM transmitter that selects a harmonic of an HF signal to reach the desired operating frequency? • D. Multiplier Signals and Emissions

  40. G8B05 Why isn't frequency modulated (FM) phone used below 29.5 MHz? • A. The transmitter efficiency for this mode is low • B. Harmonics could not be attenuated to practical levels • C. The bandwidth would exceed FCC limits • D. The frequency stability would not be adequate Signals and Emissions

  41. G8B05 Why isn't frequency modulated (FM) phone used below 29.5 MHz? • A. The transmitter efficiency for this mode is low • B. Harmonics could not be attenuated to practical levels • C. The bandwidth would exceed FCC limits • D. The frequency stability would not be adequate Signals and Emissions

  42. G8B06 What is the total bandwidth of an FM-phone transmission having a 5 kHz deviation and a 3 kHz modulating frequency? • A. 3 kHz • B. 5 kHz • C. 8 kHz • D. 16 kHz Signals and Emissions

  43. G8B06 What is the total bandwidth of an FM-phone transmission having a 5 kHz deviation and a 3 kHz modulating frequency? • A. 3 kHz • B. 5 kHz • C. 8 kHz • D. 16 kHz • Carson’s Rule BW = 2 * (Peak Deviation + Highest Modulating Frequency)BW = 2 * (5 + 3 ) = 16 Signals and Emissions

  44. G8B07 What is the frequency deviation for a 12.21-MHz reactance-modulated oscillator in a 5-kHz deviation, 146.52-MHz FM-phone transmitter? • A. 101.75 Hz • B. 416.7 Hz • C. 5 kHz • D. 60 kHz Signals and Emissions

  45. G8B07 What is the frequency deviation for a 12.21-MHz reactance-modulated oscillator in a 5-kHz deviation, 146.52-MHz FM-phone transmitter? • A. 101.75 Hz • B. 416.7 Hz • C. 5 kHz • D. 60 kHz5000 / 12 = 416.7 Hz Signals and Emissions

  46. G8B08 How is frequency shift related to keying speed in an FSK signal? • A. The frequency shift in hertz must be at least four times the keying speed in WPM • B. The frequency shift must not exceed 15 Hz per WPM of keying speed • C. Greater keying speeds require greater frequency shifts • D. Greater keying speeds require smaller frequency shifts Signals and Emissions

  47. G8B08 How is frequency shift related to keying speed in an FSK signal? • A. The frequency shift in hertz must be at least four times the keying speed in WPM • B. The frequency shift must not exceed 15 Hz per WPM of keying speed • C. Greater keying speeds require greater frequency shifts • D. Greater keying speeds require smaller frequency shifts Signals and Emissions

  48. G8B09 What do RTTY, Morse code, PSK31 and packet communications have in common? • A. They require the same bandwidth • B. They are digital modes • C. They use on/off keying • D. They use phase shift modulation Signals and Emissions

  49. G8B09 What do RTTY, Morse code, PSK31 and packet communications have in common? • A. They require the same bandwidth • B. They are digital modes • C. They use on/off keying • D. They use phase shift modulation Signals and Emissions

  50. G8B10 When transmitting a data mode signal, why is it important to know the duty cycle of the mode you are using? • A. To aid in tuning your transmitter • B. To prevent damage to your transmitter's final output stage • C. To allow time for the other station to break in during a transmission • D. All of these choices are correct Signals and Emissions

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