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Communication Systems for Control and Automation
Published in James Northcote-Green, Robert Wilson, Control and Automation of Electrical Power Distribution Systems, 2017
James Northcote-Green, Robert Wilson
Data radio, if correctly utilized, is a robust way of communication. The investment and service cost is fairly low. Especially at the VHF band, huge coverage can be achieved; 100-km jumps (no line of sight) is quite possible. The available channel spacing is normally 12.5/25 kHz. The possibility to use frequencies that are licensed in the VHF and UHF bands increases the reliability because no other user is licensed to use the same frequency. Lately, forward error correction (FEC) with interleaving has found its way into these products as well, increasing coverage and security even further. Other important features are collision avoidance, peer-to-peer functionality and radio network test functions. The speed is typically 9.6–19.2 kbps depending on channel spacing, and the typical range is 10–100 km (system dependent).
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Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[general] Amplitude modulated transmission of electromagnetic waves used for wireless signal transmission. The mechanism of operation is distinctly different from FM radio. The radio signal is generated by an alternating dipole in oscillatory fashion over the length of an antenna generating a carrier wave with a fixed frequency, which is modulated in amplitude by the superimposed signal wave. The accompanying alternating electric and magnetic field is described for the dipole (seedipole, alternating). The superposition principle applies to electromagnetic waves. The broadcast frequency range is split in the following wavelength bands. The carrier wave is denoted by three denominations. The first transmission designation is long wave radio: 148.5–283.5 kHz. Long-wave (LW-) radio generally uses 9 kHz channel spacing. Next is medium-wave (MW-) radio: 520–1,710 kHz. Channel spacing varies between 9 and 10 kHz. Medium-wave radio is associated with the generally available information channels and music for commercial use. The last band is short wave broadcasting in the 1.711–30.0 MHz range. Short-wave (SW-) radio is subdivided into 15 bands; channels are generally separated by 5 kHz (see Figure A.62).
Ultra-Narrowband Optical Comb Filter Using Sampled Fibre Bragg Gratings
Published in Arpan Deyasi, Pampa Debnath, Asit K. Datta, Siddhartha Bhattacharyya, Photonics, Plasmonics and Information Optics, 2021
Here we illustrate one efficient technique for obtaining the ultra-narrowband peaks in the comb spectrum using GS-PCFBG filter [21]. The working of ultra-narrowband comb filter has been pictorially demonstrated in Figure 8.14. The effect of Gaussian apodization on a conventional CFBG has been shown in Figure 8.14a and 8.14b. Figure 8.14a is the r.i. profile of a conventional-CFBG and its reflection spectrum. Figure 8.14b is the r.i. profile of the same CFBG but Gaussian apodized and its reflection spectrum. The reflection spectrum depicts that the Gaussian apodization reduces the bandwidth significantly. This helps to reduce the bandwidth and also lower the side-lobes. When a grating is periodically Gaussian apodized, the bandwidth of individual channels also gets decreased. Further, low index modulation may be used to provide the ultra-narrowband peaks in the reflection spectrum. In addition, it is seen that, if channel spacing is reduced, the channel-bandwidth is decreased. It is also seen that the in-channel bandwidth can be highly reduced if sampling length is increased. In Figure 8.14c, the r.i. variation of a periodically chirped grating and its reflection spectrum are shown. The reflection spectrum is actually a comb spectrum where MPS technique has been used. Further, in Figure 8.14d, it is shown that the grating is sampled periodically with a Gaussian function and its reflection spectrum. It is observed that the spectrum has the lower channel spacing and narrower channel-bandwidth. The channel bandwidth can be further lowered if the sampling length is increased. It is depicted in Figure 8.14e. The length of the individual grating section is increased and ultra-narrowband peaks have been obtained. The reflection spectrum obtained using GS-PCFBG is shown in Figure 8.15. It provides channel spacing of 13.9 GHz. The reflection spectrum of a single peak of Figure 8.15 is given in Figure 8.16, showing the 3-dB bandwidth of 450 MHz.
Investigation of a coherent dual-polarized 16-QAM 16-channel WDM FSO gamma–gamma fading system under various atmospheric losses
Published in Journal of Modern Optics, 2022
With Wavelength division multiplexing (WDM) based FSO systems, we can overcome fibre optic communication's challenges for transmitting information signals over common channels [18]. Furthermore, an increase in channel count and a reduction in channel spacing can enhance data capacity. Wavelength division multiplexing (WDM) allows for better utilization of an optical fibre's transmission capacity. An optical multiplexer combines multiple wavelengths on a single optical channel, and a de-multiplexer separates multiple signals into separate optical wavelengths at the receiving end. Optical channels in the wavelength domain can be packed relatively closely together to determine the ultimate capacity of a WDM fibre network. The optical channels in dense WDM (DWDM) applications are closely spaced.