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Noise in analogue communications systems
Published in J. Dunlop, D. G. Smith, Telecommunications Engineering, 2017
One conclusion we may draw from these figures is that for a given radiated power a FM transmitter will have a greater range than a DSB-AM transmitter, provided that the SNR at the FM detector input is sufficiently high for the noise to produce narrowband frequency modulation of the carrier. In other words, the FM system must be operating above the threshold level. This threshold level is related to both the frequency deviation and the SNR at the detector input. For large values of Δfc the threshold occurs at a SNR of about 13 dB. The conditions required for FM to exhibit its SNR improvement properties are that β > 1/√3 [assuming f0 = fm in Eqn (4.46)] and the SNR at the detector input must exceed 13 dB. If the SNR at the detector input is below the threshold value, the output SNR decreases rapidly and ultimately becomes poorer than the equivalent AM value.
Modulation Systems and Characteristics
Published in Jerry C. Whitaker, Power Vacuum Tubes, 2017
The FM transmission/reception system offers significantly better noise-rejection characteristics than AM. However, FM noise rejection is more favorable at low modulating frequencies than at high frequencies because of the reduction in the number of sidebands at higher frequencies. To offset this problem, the input signal to the FM transmitter may be preemphasized to increase the amplitude of higher-frequency signal components in normal program material. FM receivers utilize complementary de-emphasis to produce flat overall system frequency response.
Electronic Communications
Published in Dale R. Patrick, Stephen W. Fardo, Electricity and Electronics Fundamentals, 2020
Dale R. Patrick, Stephen W. Fardo
An FM transmitter regardless of its power rating or operational frequency has a number of fundamental parts. The oscillator is responsible for the development of the RF carrier. Many FM transmitters employ direct oscillator modulation, meaning that the frequency of the oscillator is shifted by direct application of the modulation component. The RF signal is then processed by a number of amplifiers. The power amplifier ultimately feeds the FM carrier into the antenna for radiation.
A Comprehensive Survey on GNSS Interferences and the Application of Neural Networks for Anti-jamming
Published in IETE Journal of Research, 2021
Kambham Jacob Silva Lorraine, Madhu Ramarakula
Unintentional (accidental) interference: Due to emerging wireless communication systems, all the sources which emit RF signals close to or in the frequency bands where the GNSS receiver operates can cause unintentional interference. It occurs commonly due to the harmonics of RF systems, spurious emissions from electrical devices, and signal leakage out of the allocated bandwidth. Figure 4 shows the types of unintentional interferences. Potential sources of this interference are mobile and fixed Very High Frequency (VHF) communications, harmonics of television stations, certain Radio Detection and Ranging System (RADAR) transmitters, mobile satellite communications, Amplitude Modulated (AM), and Frequency Modulated (FM) transmitter harmonics, signals from inter-system (self-interference) and intra-system (like GALILEO, GPS). Sometimes, the signal from ground-based transmitters like Pseudolites can also act as interference to the GNSS systems due to the near-far effect [8].