The louder the voice signal in an FM transmitter the greater the frequency deviation of the modulator. If we are over deviating the frequency then we need to reduce the amplitude of our voice. Therefore the correct answer is to talk farther away from the microphone or not talk so loudly.
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There are many things that can cause interference with radio signals. All three of those listed here can cause interference, therefore the correct answer is "All of these choices are correct".
Fundamental overload - This is a case when the transmitted signal is so strong that it overloads the receiver which prevents proper reception of the desired signal.
Harmonics - When a sine wave is distorted (not pure) it creates harmonics that are integer multiples of the fundamental frequency; these harmonics end up getting into receivers at these harmonic frequencies interfering with operation on those frequencies. See this reference: 5.0 Transmitter Harmonic Emissions.
Spurious emissions - There are a number of undesirable emissions that can interfere with normal signal reception. Most of these can be termed Spurious emissions. From ITU, 1.145 "Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products but exclude out-of-band emissions."
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Sometimes a strong RF signal can get into the circuitry of other devices, such as stereos, telephones and audio amplifiers in public address (PA) systems, and be demodulated such that they inadvertently act as a radio receiver. Take a look at the FCC Notice labels on modern electronic devices in your home to see recommendations on how to reduce interference. Amateur radio operators can reduce emissions that may interfere with a neighbor's electronic devices by installing filters, reorienting antennas or moving to a new location.
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Making sure your station is functioning properly and does not interfere with your electronic devices is always a great starting point. As you look at the distractor answers they each have something that is quite unreasonable so you can discount them.
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Sometimes it may take more than one action or filter type to prevent interference. Each of these techniques are appropriate choices such that the correct answer is "All of the choices are correct". If you cannot solve the interference problem yourself, ask a fellow ham to help assist you in finding a solution.
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Cooperation with others is the best way to start solving an interference problem. Many devices, especially digital computers and peripherals, generate RF interference. Turning off devices one at a time is a good way to locate an offending device. For more information see: RF interference
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The key word in the question is "mobile transmitter" which means a transciever in your vehicle. The alternator of your vehicle can generate noise that can tag along with the signal transmitted by your radio. Sometimes the whine varies with the RPM of the engine. The best way to prevent this interference is to put filters on the DC power line going to the transceiver.
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How do each of these cause your signal to be distorted or unintelligible?
"Your transmitter may be slightly off frequency" - If your transmitter is slightly off frequency the receiver will not be able to demodulate the signal and it may sound garbled, distorted and low in volume.
"Your batteries may be running low" - When your batteries are low the audio amplifier cannot generate the proper amplitude signals; the signal is limited by the lower than normal voltage which clips the signal causing it to be distorted.
Also, "You could be in a bad location" - As in real estate, location, location and location are vital. Multipath signals can cause an interference pattern that can make the received audio sound bad.
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Your own transmitter output can be picked up by the sensitive circuits inside your microphone. This is called RF feedback. The symptom is that the transmission may be distorted, garbled or unitelligible.
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BER is the acronym for Bit Error Rate. In digital communication system the data is sent as individual bits of 1 or 0. Errors in the digital bit streams are measured as a Bit error rate (number of errors divided by total number of bits and displayed as a percentage).
The distractors answers are non-sense.
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