The UK Legislation and Communication Limits
Aviation communication encompasses the process where two or more aircrafts converse through radio equipment installed in them. The manner in which aircrafts are constructed makes it hard for one to see what is directly in front of them. Safety is a very important component in aviation. This necessitates the need to have a method of communication like the wireless radio to aid in communication among the personnel involved in various activities. Even though the process of communication requires the interaction of complex machines, the person handling them must be proficient in the preferred communication language. All radio equipment used for communication in an aircraft must be approved by the safety regulation group (SRG) which is a branch of the civil aviation authority.
The UK legislation limits aircraft communication in a number of ways. The legislations apply to aircrafts that are registered in the UK and those that fly over the territorial sea within its jurisdiction. First of all, the apparatus used for communication must be compliant with the GSM standard EN 301511 (Smith et al., 2017). Secondly, the limits within which the frequency bands are to operate are 1710-1785 and 1805-1880. Thirdly, the communication instruments must only be used for purposes of mobile communication within the aircraft when the aircraft is 3000 metres above the ground or more (Baddoo, Naylor & Myers, 2015). When the communication gadgets are in use, they must not cause or contribute to interferences to any other wireless telegraphy.
Before communication equipment is mounted on an aircraft, it must first be approved by the SRG. This is encompassed in the wireless telegraphy act where the users of the communication equipment in the aircraft are mandated to have a valid operational licence. That is, a flight radio telephony operator’s licence. Glider pilots are exempted from this since they operate at specific glider frequencies. The radio spectrum within which the equipment function is also regulated. Thus, the users must be trained before they are given the mandate to operate. Additionally, measures are also taken to ensure that the equipment operate within the specified limits with minimal interference to systems used by other users. Under the WT Act, aircrafts that use licences that are not valid and cause interferences in the process can be prosecuted. Even complains of interference can warrant such tough actions. The Wireless Telegraphy Act 2006 which limits the installation and transmission of radio frequencies without a valid licence (Adhikari, Jain & Jamadagni, 2015). Routine checks are often carried out from time to time so as to ensure that the equipment installed has the right specifications and that they do not cause any interference while in operation. The licences issued cover equipment used within the UK and those used on aircrafts that fly out of the UK.
Principles of Operation of a Radio Receiver
The AM transmitter has two frequencies within which it operates. That is, the audio frequency units and the radio frequency units. The radio frequency unit generates the radio frequency carrier wave. The carrier wave is generated as a constant-frequency, constant-amplitude sine wave. For the carrier to attain sufficient amplitude it must be amplified through one or more stages for the high power required by the antenna to be attained (Subhan et al., 2014). The transmitter also has a circuitry section which receives the signals from the microphone and raises their amplitude to a unit needed for full modulation of the carrier. The modulator is the last stage where a signal from it is applied to the carrier. The frequency of the signal is indicated by line on the horizontal axis while the amplitude is indicated by the height of the frequency line.
The function of a radio receiver is to convert the radio waves received into a form that is usable. The antenna on the receiver intercepts electromagnetic waves and converts them into alternating currents that are forwarded to the receiver. The receiver in turn extracts the information needed. The electronic filters in the receiver isolate the required radio frequency from the other signals that the antenna picks (Woo, Park & Kwon, 2015). The power of the signal is then enhanced further by an electronic amplifier before it is processed further and finally demodulated to recover the information desired.
The strength of the signal of the radio waves reduces as they move further away from the transmitter and this limits the range within which a radio frequency can be received. The range also depends on the transmitters’ power, its sensitivity, internal and atmospheric noise and the geographical features like hills that are between the transmitter and the receiver (Xie et. al., 2016). The transmission of the AM radio band waves follows the earth contour. Thus, it travels as ground waves. The FM waves on the other hand, have a higher frequency and they cannot travel distances far beyond the visual horizon. The distance to which they are received is thus limited to 40 miles (Aliparast, 2016). This makes them vulnerable to geographical features that block them. Even so, thee waves are not susceptible to interference by radio noise. Their frequency response is way better with minimal audio distortion compared to the AM waves.
The band pass filter in a receiver has resonant circuits that connect the input of the antenna to the ground. When a signal is received at a resonant frequency, the impedance of the circuit increases thus passing the signal from the desired radio station to the receiver. On the contrary, when the impedance of the circuit is low, the signals are conducted to the ground. When the receiver picks up the power of the radio waves, it reduces the square of the distance between it and the antenna (Haberl et. al., 2017). This happens regardless of the distance between the transmitter and the receiver. For the power of the recovered signal to be increased, it passes through an amplifier circuit which relies on the power of the wall plug or the batteries to increase the amplitude of the voltage or the current. The transistors do the amplification function in most of the modern receivers.
Receiver Stages in the Amplification Process
The receiver has numerous stages in the amplification process. The signal goes through the band pass filter which amplifies it to create a more powerful frequency that can drive the demodulator conveniently. The audio signal that comes out of the demodulator is enhanced to make it even more powerful so that it can operate the speaker. Sensitivity is the unit employed in measuring the degree to which radio receiver are amplified. Through this, the minimal strength of the signal for any given station at the antenna is measured in microvolts for the signal to be clearly received at a recommended threshold of signal-to-noise ratio. Signals can be amplified to any degree (Chen et. al., 2018). Thus, the sensitivity of a receiver is not determined by the degree to which waves can be amplified but the random electronic noise that is in the circuit which drowns signals that are weak.
After radio signals have been received, filtered, and amplified, the receiver extracts information containing modulation signals from the carrier wave of the modulated radio frequency. The detector, which is also the demodulator, does this work. For optimum results to be realized, each type of demodulator must be matched to a specific type of demodulator. A combination of the FM and the AM detector rarely works and if it does, it is poor (Liu et. al., 2017). Most of the type modulation is employed only if specialized functions have to be realized.
References
Adhikari, B., Jain, P. and Jamadagni, H.S., 2015, July. An ultra-wideband frequency Domain receiver for software defined radio applications. In Electronics, Computing and Communication Technologies (CONECCT), 2015 IEEE International Conference on (pp. 1-6). IEEE.
Aliparast, P., 2016. Design and implementation of a high efficiency RF power amplifier for S-band telemetry subsystems. AEU-International Journal of Electronics and Communications, 70(9), pp.1311-1320.
Baddoo, G.J.A., Naylor, M. and Myers, A.J., Thales Holdings Uk Plc., 2015. Aircraft radio system. U.S. Patent 9,169,018.
Chen, T., Li, K., Zuo, Y. and Zhu, B., 2018. Hybrid quantum receiver for quadrature amplitude modulation coherent-state discrimination beating the classical limit. Applied Optics, 57(4), pp.817-822.
Haberl, M., Sanftl, B., Trautmann, M., Weigel, R. and Koelpin, A., 2017, January. A direct RF-to-baseband quadrature subsampling receiver using a low cost ADC. In Radio and Wireless Symposium (RWS), 2017 IEEE (pp. 144-146). IEEE.
Liu, L., Grombacher, D., Auken, E. and Larsen, J.J., 2017, September. A Multichannel, Low Noise Surface NMR Receiver System with Wireless Connections to Signal and Reference Coils. In 23rd European Meeting of Environmental and Engineering Geophysics.
Smith, M., Moser, D., Strohmeier, M., Lenders, V. and Martinovic, I., 2017. Analyzing privacy breaches in the aircraft communications addressing and reporting system (acars). ArXiv preprint arXiv: 1705.07065.
Subhan, S., Klumperink, E.A., Ghaffari, A., Wienk, G.J. and Nauta, B., 2014. A 100–800 MHz 8-Path Polyphase Transmitter with Mixer Duty-Cycle Control Achieving $<-$40 dBc for ALL Harmonics. IEEE journal of solid-state circuits, 49(3), pp.595-607.
Woo, J.L., Park, S. and Kwon, Y., 2015, May. A wideband envelope-tracking CMOS linear transmitter without digital predistortion. In Radio Frequency Integrated Circuits Symposium (RFIC), 2015 IEEE (pp. 367-370). IEEE.
Xie, G.T., Yu, H.Y., Zhu, Y.J. and Ji, X.S., 2016. A linear receiver for visible light communication systems with phase modulated OFDM. Optics Communications, 371, pp.112-116.
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