% FILENAME = N29.TXT % Interference and Filtering % Release version 4, June 2004 %QUESTION: 1 #29.1 Electromagnetic compatibility is: two antennas facing each other the ability of equipment to function satisfactorily in its own environment without introducing intolerable electromagnetic disturbances more than one relay solenoid operating simultaneously the inability of equipment to function satisfactorily together and produce tolerable electromagnetic disturbances % ans 2 %QUESTION: 2 #29.2 On an amateur receiver, unwanted signals are found at every 15.625 kHz. This is probably due to: a low-frequency government station a remote radar station radiation from a nearby TV line oscillator none of these % ans 3 %QUESTION: 3 #29.3 Narrow-band interference can be caused by: transmitter harmonics a neon sign a shaver motor lightning flashes % ans 1 %QUESTION: 4 #29.4 Which of the following is most likely to cause broad-band continuous interference: an electric blanket switch a refrigerator thermostat a microwave transmitter poor commutation in an electric motor % ans 4 %QUESTION: 5 #29.5 If broadband noise interference varies when it rains, the most likely cause could be from: underground power cables outside overhead power lines car ignitions your antenna connection % ans 2 %QUESTION: 6 #29.6 Before explaining to a neighbour that the reported interference is due to a lack of immunity in the neighbour's electronic equipment: disconnect all your equipment from their power sources write a letter to the MED make sure that there is no interference on your own domestic equipment ignore all complaints and take no action % ans 3 %QUESTION: 7 #29.7 A neighbour's stereo system is suffering RF break-through. One possible cure is to: put a ferrite bead on the transmitter output lead put a capacitor across the transmitter output use open-wire feeders to the antenna use screened wire for the loudspeaker leads % ans 4 %QUESTION: 8 #29.8 When living in a densely-populated area, it is wise to: always use maximum transmitter output power use the minimum transmitter output power necessary only transmit during popular television programme times point the beam at the maximum number of television antennas % ans 2 %QUESTION: 9 #29.9 When someone in the neighbourhood complains of TVI it is wise to: deny all responsibility immediately blame the other equipment inform all the other neighbours check your log to see if it coincides with your transmissions % ans 4 %QUESTION: 10 #29.10 Cross-modulation is usually caused by: rectification of strong signals in overloaded stages key-clicks generated at the transmitter improper filtering in the transmitter lack of receiver sensitivity and selectivity % ans 1 %QUESTION: 11 #29.11 When the signal from a transmitter overloads the audio stages of a broadcast receiver, the transmitted signal: can be heard irrespective of where the receiver is tuned appears only when a broadcast station is received is distorted on voice peaks appears on only one frequency % ans 1 %QUESTION: 12 #29.12 Cross-modulation of a broadcast receiver by a nearby transmitter would be noticed in the receiver as: a lack of signals being received the undesired signal in the background of the desired signal interference only when a broadcast signal is received distortion on transmitted voice peaks % ans 2 %QUESTION: 13 #29.13 Unwanted signals from a radio transmitter which cause harmful interference to other users are known as: rectified signals re-radiation signals reflected signals harmonic and other spurious signals % ans 4 %QUESTION: 14 #29.14 To reduce harmonic output from a transmitter, the following could be put in the transmission line as close to the transmitter as possible: wave trap low-pass filter high-pass filter band reject filter % ans 2 %QUESTION: 15 #29.15 To reduce energy from an HF transmitter getting into a television receiver, the following could be placed in the TV antenna lead as close to the TV as possible: active filter low-pass filter high-pass filter band reject filter % ans 3 %QUESTION: 16 #29.16 A low-pass filter used to eliminate the radiation of unwanted signals is connected to the: output of the balanced modulator output of the amateur transmitter input of the stereo system input of the mixer stage of your SSB transmitter % ans 2 %QUESTION: 17 #29.17 A band-pass filter will: pass frequencies each side of a band attenuate low frequencies but not high frequencies attenuate frequencies each side of a band attenuate high frequencies but not low frequencies % ans 3 %QUESTION: 18 #29.18 A band-stop filter will: pass frequencies each side of a band stop frequencies each side of a band only allow one spot frequency through pass frequencies below 100 MHz % ans 1 %QUESTION: 19 #29.19 A low-pass filter for a high frequency transmitter output would: attenuate frequencies above 30 MHz pass audio frequencies below 3 kHz attenuate frequencies below 30 MHz pass audio frequencies above 3 kHz % ans 1 %QUESTION: 20 #29.20 Installing a low-pass filter between the transmitter and transmission line will: permit higher frequency signals to pass to the antenna ensure an SWR not exceeding 2:1 reduce the power output back to the legal maximum permit lower frequency signals to pass to the antenna % ans 4 %QUESTION: 21 #29.21 A low-pass filter may be used in an amateur radio installation: to attenuate signals lower in frequency than the transmission to attenuate signals higher in frequency than the transmission to boost the output power of the lower frequency transmissions to boost the power of higher frequency transmissions % ans 2 %QUESTION: 22 #29.22 Television interference caused by harmonics radiated from an amateur transmitter could be eliminated by fitting: a low-pass filter in the TV receiver antenna input a high-pass filter in the transmitter output a low-pass filter in the transmitter output a band-pass filter to the speech amplifier % ans 3 %QUESTION: 23 #29.23 A high-pass filter can be used to: prevent interference to a telephone prevent overmodulation in a transmitter prevent interference to a TV receiver pass a band of speech frequencies in a modulator % ans 3 %QUESTION: 24 #29.24 A high-pass RF filter would normally be fitted: between transmitter output and feedline at the antenna terminals of a TV receiver at the Morse key or keying relay in a transmitter between microphone and speech amplifier % ans 2 %QUESTION: 25 #29.25 A high-pass filter attenuates: a band of frequencies in the VHF region all except a band of VHF frequencies high frequencies but not low frequencies low frequencies but not high frequencies % ans 4 %QUESTION: 26 #29.26 An operational amplifier connected as a filter always utilises: positive feedback to reduce oscillation negative feedback random feedback inductors and resistor circuits only % ans 2 %QUESTION: 27 #29.27 The voltage gain of an operational amplifier at low frequencies is: very high but purposely reduced using circuit components very low but purposely increased using circuit components less than one undefined % ans 1 %QUESTION: 28 #29.28 The input impedance of an operational amplifier is generally: very high very low capacitive inductive % ans 1 %QUESTION: 29 #29.29 An active audio low-pass filter could be constructed using: zener diodes and resistors electrolytic capacitors and resistors an operational amplifier, resistors and capacitors a transformer and capacitors % ans 3 %QUESTION: 30 #29.30 A filter used to attenuate a very narrow band of frequencies centred on 3.6 MHz would be called: a band-pass filter a high-pass filter a low-pass filter a notch filter % ans 4