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Abstract- In this paper, we discuss about the latest news on radio frequency modulation technique include amplitude modulation, phase modulation and frequency modulation . We also discuss about the application in nowadays. Further research or ongoing research and development activities have also been reviewed in this paper.
Keywords: radio frequency modulation; amplitude modulation; frequency modulation.
A device that takes a baseband input signal and outputs a radio frequency-modulated signal is called radio frequency modulator (RF modulator). RF modulators are present in almost all the communication devices that are present today. Radio frequencies usually lie in the range of 3 to 300 GHz. For the electronic devices, RF modulator explains the idea of the carrier signal in the process of modulation. This is often a beginning step in transmitting signals, whichever across open air via an antenna or transmission to another device such as a television.
A modulator is a device that modulates electrical signals onto a dissimilar type of signal. Generally, there are two main types of modulation techniques which are digital modulation and analog modulation. It is called digital modulation when modulating signal is digital and it is called analog modulation when modulating signal is analog. Digital type is further classified according to the feature of carrier wave is customized. This includes frequency modulation where frequency of the carrier wave is assorted according to amplitude of modulated signal, and many such techniques. Modern RF modulators carry out digital modulation.
Ways of RF modulation
There are three main ways in which a radio communications or RF signal can be modulated that is amplitude modulation, frequency modulation and phase modulation. Each type of modulation has its own pros and cons, and accordingly they are all used in dissimilar radio communications applications. In addition to the three main basic forms of modulation or modulation techniques, there are many variants of each type. These modulation techniques are used in a variety of applications, some for analogue applications, and others for digital applications. 
2.1 Modulation technique
A RF modulator can change signals from one form to the other form. There are lots of other modulation techniques that can be used, like the Phase Shift Key (PSK), where it can be used to modulate the signals with the radio frequency. Some modulation schemes like Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and Quadrature Amplitude Modulation are based on varying the amplitude of the signal. These require a linear power amplifier in the output stage of the transmitter to avoid frequency splatter. Constant envelope modulation schemes like Gaussian Minimum Shift Keying (GMSK) do not require a linear power amplifier. Linear power amplifiers are less power proficient than non linear amplifiers.  This is a vital consideration for battery powered radios.
2.1.1 Amplitude Shift Keying
For the amplitude Shift Keying, digital signal is used to switch the carrier amplitude into low and high. Amplitude Shift Keying is also called on-off keying (OOK) and interrupted continuous wave (ICW). From digital signal, the pulses will change the amplitude of the carrier signal. Representation of two amplitudes for which bit 0 represent zero amplitude and bit 1 represent maximum carrier amplitude is called binary value.
2.1.2 Frequency Shift Keying
In addition, for the Frequency Shift Keying, the generations of an FSK waveform at the transmitter can be done by generating two amplitude shift keying waveform and adding them together with a summing amplifier. Binary signal 1 will be multiply with binary 0 at second carrier frequency and a carrier signal. Both frequencies do not have the same value frequency deviation. Both amplitude shift keying outputs from two multipliers will add together by adder to produce an FSK signals. Generation of FSK signal can be developed using three methods which are using switch, using VCO and using multiplier.
2.1.3 Phase Shift Keying
Moreover, for the Phase Shift Keying, the phase of the carrier is set to zero degree and hundred eighty degreeor posite ninthy degree and negative ninthy degree depending on the digital signal. The Phase Shift Keying can be generated by using inverter to convert binary one to negative one signal. Both of the signals will be fed to one switch to produce phase shift keying signal. The advantages of the Phase Shift Keying are having the same bandwidth with the Amplitude Shift Keying and it is immune to noise.
Today, most of the information is transferred using radio communications systems. We used both the analogue radio communications systems and digital or data radio communications links. However, one of the basic aspects of any radio communications transmission system is modulation. In order for a steady radio signal can carry information, it must be altered or modulated in one way so that the information can be conveyed from one place to another.
2.2 Importance of RF modulator
RF modulation is vital in TV modulators. In order to put on show picture information on early analog televisions, the data must be modulated to the form that the television can take. Televisions can only accept signals through the aerial connector. Input signal from TV station, are transmitted over the air, after that, it is received by an antenna and fed into the television. This usually means combining the data with a carrier wave at a consistent frequency.
For an older television that only has a cable or antenna connection, an RF Modulator is needed in order to connect a DVD player or DVD recorder to the television. The function of an RF modulator is simple. The RF modulator change the video or audio output of a DVD player into a channel signal that is well-matched with a television's cable or antenna input.
There are many RF modulators available, but all function in a similar fashion. The main characteristic of an RF modulator is that makes it completely suitable for use with DVD. Setting up an RF modulator is simple. Firstly, television's cable output is plugged into the cable input connection of the RF modulator and the DVD player into the RF modulator's inputs. Then, a ordinary RF cable is connected from the RF modulator to the television. After that, whichever the channel 3 or 4 output is selected on the back of the RF modulator. Lastly, the TV is turned on and the RF modulator will mechanically detect the cable input for the TV. When we want to watch DVD player, we can just put the television on channel 3 or 4, turn the DVD player on and the RF modulator will automatically detect the DVD player and will display movie. When the DVD player is turn off, the RF Modulator should revert back to normal television viewing.
The need to use RF Modulator is when we have a very poor picture quality in DVD player. The function of an RF modulator is simple. The RF modulator converts the video output of a DVD player or video game into a channel 3/4 signal that is well-matched with a TV's cable or antenna input. There are many RF modulators available, but all function in a similar fashion.
During the 1980s and early '90s, it was common for video game systems that did not have internal RF modulators to make available external units that connected to the antenna jacks of a television. One reason for this is that a device which outputs an RF signal must in general be certified by regulatory authorities. Thus, by having an external RF modulator, only the modulator itself needed to be licensed, rather than the entire video game system.
TV modulators usually feature analog pass through, meaning that they take input both from the device and from the usual antenna input, and the antenna input passes through to the TV, with minor insertion loss due to the added device. In some cases the antenna input is always passed through, while in other cases the antenna input is turned off when the device is output a signal, and only the device signal is sent forward, in order to reduce the interference.
Here are some forms of applications on RF Modulator. RF modulator is a significant component in all forms of radio communication equipment. The advantage of an RF modulator is that it makes communication over long distances possible. Any signal that needs to be transmitted over air cannot be directly transmitted through an antenna in original form, as it may get damped or lose its energy over long distances. Hence, RF modulators are used in most signal transmitters. They take in the electrical signal and apply it or modulate it to a high frequency radio wave, which is then transmitted.
Radio waves can be transmitted over long distances, without getting damped and the signal is received on the other end. At the receiving end the signal is demodulated, that is changed back to original form and then used. Radio stations have RF modulators in their transmitting equipment. Thus, RF modulators are used in every radio communication device ranging from aviation, ham radio, mobile devices, radar systems and many others.
3.1 RF power sensor
There are two main types of RF power sensor which are thermal and diode sensor. The thermal types have been around for many years. However, since the beginning at the 1990s the industry needed capabilities the thermal sensors could not provide because of the new types of modulation being used. Now, eighty to ninety percent of all power sensors are diode biased. Although, thermal sensors are slow over a relatively large portion of their dynamic range and they only can measure the average power of a signal, but they still deliver the most accurate measurement results. One reason is the effect of harmonics and non-harmonics can be predicted very well.
Nowadays, diode based RF power sensor offer sufficient accuracy for the majority of applications. The diode based type need very careful design, but they offer many advantages in term of functionality, speed and dynamic range. Actually, they also can measure down to level of around -60 to -70 dBm where the thermal power sensors typically have a lower range limit of between -30 to -35 dBm. By reading the peak power or the rise time of a pulse and by making statistically evaluations of the envelope within solve milliseconds are typical tasks for the new design.
3.2 New product
Thomas Reichel, Head of Power Master Development at Rode and Schwarz has launched his new product which is 67 GHz power sensor. The speciallity of this product is on their frequency limit and the accuracies are very impressive. The major challenges of 67 GHz sensor is on mechanical problems. At these frequencies the dimensions are very small. In fact, mechanically matching the coaxial feeder to the transducer while maintaining the impedance match are quite exacting. There are new methods for making the transition. Thomas took a radical look at the design and came up with what we call a soft transition which is manufactured using photo-lithography to give the required accuracy. These power sensor also have many signal generators, network analyzers, spectrum analyzers and the like that extend to these frequencies and calibration facilities for these will need RF power meters that are capable of operating at these frequencies. In addition, there is growing number of 60 GHz short range communications systems that are being introduced and again these need power meters during the design, manufacture and for servicing and repair.
In conclusion, RF modulation is very important in our daily life. Hence, more research and development should be done on this topic. Coming to a broader field, radio frequency modulators are used widely in the defense and aviation industries. In industries, the information that is sent to flights also need to be radio frequency modulated. The construction of the RF modulator, is thus done with reference to the rationale it is going to solve.
Grateful thanks to Dr. Sevia Mahdaliza M. Idrus for guiding us in the process of doing this project. We are also appreciate our friends and course mate for sharing their knowledge and information with us.