Linear ic vco and function generators can generate a direct fm output waveform that is relatively stable, accurate, and directly proportional to the input modulating signal. Fm reactance modulator proof of the theory all about circuits. Frequency modulation software free download frequency modulation top 4 download offers free software downloads for windows, mac, ios and android computers and mobile devices. May 26, 2017 viewing fm frequency modulation signal shape. Modeling and testing of a digital distance relay using matlab simulink page link.
The lc modulator is a circuit that is resonant at the frequency that is to be phase modulated. Why armstrong method of fm is superior to reactance modulator. Complete notes download link ac notes analog communication system notes pdf free download. Generation of frequency modulation varactor diode modulator. Difference between resistance and reactance compare the. State the term given to the total opposition z in an ac circuit. Ppt frequency modulation fm powerpoint presentation. Pdf 92cm9806 92cm9807 gridn22 92cm98ii 92cm9803 reactance modulator 9806. Hence crystal oscillators can be used in armstrong method. The varicap is connected across the tank circuit of the oscillator. When the reactance tube is connected across the tank circuit with no modulating voltage applied, it will affect the frequency of the oscillator. Therefore frequency stability is better than reactance modulator. For direct generation of fm signal reactance modulator and varactor diode modulator used.
Ans reactance modulator is direct fm, where as armstrong method is indirect fm. Furthermore, this video explain briefly about the operation of reactance modulator. Us2279659a us6578a us657837a us2279659a us 2279659 a us2279659 a us 2279659a us 6578 a us6578 a us 6578a us 657837 a us657837 a us 657837a us 2279659 a us2279659 a us 2279659a authority us united states prior art keywords frequency circuit generator tube means prior art date 193704 legal status the legal status is an assumption and is not a. Fm reactance modulator a direct fm modulator using a jfet as the active device. In the stabilized reactance modulator afc system, a. Fm reactance modulator proof of the theory all about. The circuit shown is the basic circuit of a fet reactance modulator, which behaves as a threeterminal reactance that may be connected across the tank circuit of the. Write the formula for impedance, and calculate the impedance in a series circuit when the values. In a system for frequencymodulating a wave in correspondence with the instantaneous amplitude of a signal, the combination comprising a wave generator provided with a resonant circuit formed by a condenser in parallel with an inductor having a ferromagnetic core, a frequencymodulator including an electron discharge tube having cathode, grid. I have not drawn the complete circuit of the oscillator, as it could be any type. Fm modulation system fm transmitter, reactance modulator.
The rc circuit now appears to be purely capacitive. Now, this modulating audio is applied to the varactor diode in the reactance modulator causing the frequency of the quartz crystal to change up and down from the centre frequency. The reactance circuit appears capacitive in nature to the master oscillator. An electrontube circuit, used to produce phase or frequency modulation, in which the reactance is varied in accordance with the instantaneous amplitude of. Here you can download the free lecture notes of analog communication system pdf notes ac notes pdf materials with multiple file links to download. Frequency multiplier antenna a u d i o i n p u t power section buffer amplifier acts as a constant high impedance load on the oscillator to help stabilize the oscillator frequency. Sep 19, 2016 direct method in direct fm generation method, the instantaneous frequency of the carrier is changed directly in proportion with the message signal. Like resistance, reactance it is measured in ohms, but is separate from the opposition to current caused by any internal. The only difference is that in the square law modulator, the diode is operated in a nonlinear mode, whereas, in the switching modulator, the diode has to operate as an ideal switch. Write the formula for determining total reactance x. Reactance modulator circuit operation and troubleshooting. Analog communication pdf notes book starts with the topics covering introduction ac, dsb modulation, ssb modulation, angle modulation concepts, angle modulation methods, noise etc. Fm reactance modulator a direct fm modulator using a jfet.
The pa combines the rf carrier and the modulating signal in the power amplifier to produce the amplitudemodulated signal output for transmission. The exciter section contains the carrier oscillator, reactance modulator and the buffer amplifier. In the absence of a modulating signal, a continuous rf carrier is radiated by the antenna. Frequency modulation software free download frequency. A combination of these three components in rlc circuits makes impedance on the current path. Good day,gentlemen i would like to show you an experience on designing bjt fm reactance modulator. A reactance modulator is a circuit that uses a transistor amplifier that acts like either a variable capacitor or an inductor.
Download fulltext pdf reactance theory 40 years later article pdf available in zeitschrift fur sozialpsychologie 371. A detector circuit is used to trigger the current injection at the appropriate instant. In this case, the reactance looks like a variable capacitor in the oscillators tank circuit. Frequency modulated transmitter in frequency modulation fm the modulating.
Like resistance, reactance it is measured in ohms, but is. Spectra have a typical trapezoidal shape in linear frequency and amplitude in decibels. Bear in mind,that using bjt as reactance modulator have some nonlinear. Q2 is the modulator and is connected to the circuit so that its collectortoemitter capacitance c ce is in parallel with a portion of the rf oscillator coil, l1. May 27, 2017 good day,gentlemen i would like to show you an experience on designing bjt fm reactance modulator. Modeling and testing of a digital distance relay using matlab simulink posted by. Us6864755b2 switched reactance modulated eclass oscillator. Resistors r2 and r3 establish a voltage divider network that biases q1.
Let the modulating and carrier signals be denoted as m. Simply feed the modulating audio to a varactor diode and the diode will bring about frequency deviations of the quartz crystal proportional to the modulating audio. With no modulation, the oscillator generates a steady center frequency. Find out information about reactance tube modulator. Any changes or mistake please leave it in the comment below. Figure 24 shows you the block diagram of a frequencymodulated transmitter. Switching modulator is similar to the square law modulator. Find out information about reactancetube modulator. The capacitive reactance of c at the oscillator frequency is made five to ten times larger than the value of series resistance. Reactancetube modulator article about reactancetube. The transistor reactance modulator shown in the figure is to be used in an fm transmitter. Calculation of the input impedance of reactance modulator. Most of us are familiar with resistance at least we think we are.
The frequency multiplier section, which features several frequency multipliers. Download ac unit 4 ac notes analog communication pdf free download unit v angle modulation methods. Phase modulation is the emission produced by a reactance modulator connected to an rf power amplifier. Pdf analog communication system pdf notes ac notes sw. The reactance modulator it is that easy to produce frequency modulation. Fieldeffect transistor reactance circuits by gary dale clark captain, united states marine corps b. The triode unit is useful as a reactance modulator.
So we end up with a frequencymodulated wave as depicted above in figure 4. Fm transmitter fm transmitter block diagram direct method. The formula for inductive reactance mult iplies the angular velocity of the ac wave by the value of inductance. Ppt frequency modulation fm powerpoint presentation free. Direct pm angle modulation in which the frequency of the carrier is deviated indirectly by the modulating signal. The modulating signal applied to a varicap causes the reactance to vary. When the circuit is connected across the tuned circuit of an oscillator, the oscillator. The value of c should be chosen for low reactance at the operating frequency. There are various designs of phase modulators that are referred to as reactance modulators and the lc phase modulator is one form of a reactance modulator. Q1, along with its associated circuitry, is the oscillator.
Jun 07, 2017 thus, the key difference between resistance and reactance is that the resistance is a real part of the impedance of a component whereas reactance is an imaginary part of the impedance of a component. Provided that certain simple conditions are met, the impedance z, as seen at the input terminals a a of figure 511, is almost entirely reactive. Fm reactance modulator a direct fm modulator using a jfet as. Q2 is the modulator and is connected to the circuit so that its collectorto emitter capacitance c ce is in parallel with a portion of the rf oscillator coil, l1. Direct method in direct fm generation method, the instantaneous frequency of the carrier is changed directly in proportion with the message signal. The exciter section contains the carrier oscillator, reactance modulator and the buffer amplifier the frequency multiplier section, which features several frequency multipliers the power output section, which includes a low.
But few of us really understand reactance and its relationship to resistance. Generation of fm waves, direct method, parametric variation method, varactor diode, reactance modulator, indirect method. Apr 25, 2015 this is our assignment in chapter frequency modulation. Figure 212 shows a typical frequencymodulated oscillator stage operated as a reactance modulator. Fm modulators and transmitters sonoma state university. The voltage across the oscillator tank circuit l1 and c1 is also in parallel with the series network of r1 and c7. Variable reactance means for frequency modulating an oscillator.
Variable reactance means for frequency modulating an. Resistance, reactance and impedance a primer douglas brooks, phd ultracad design, inc. The lm1596lm1496 are doubled balanced modulatordemodulators which produce an output voltage proportional to the product of an input signal voltage and a switching carrier signal. In one embodiment of the invention, the modulated class e oscillator achieves high coil currents. Transistor q1 makes up the reactance modulator circuit. Part 2, reactance this is part 2 of a 3part series on resistance, reactance and impedance. Ac notes analog communication system notes pdf free. This power point presentation presents the fm transmission system, stereo fm, receiver, transmitter, generation, transmission, reception. This is our assignment in chapter frequency modulation. The reactance modulator changes the instantaneous phase angle of the carrier, generating phase modulated signals. In the stabilize reactance modulator afc system, a. More particularly, my present invention relates to variable condensers of a type whose reactance may be varied from relatively low frequencies up to a rate corresponding to frequencies of millions of cycles per second.