## Demodulation

W hen the radiated modulated carrier signal reaches the receiving point, the signal or intelligence must be extracted therefrom. The process by which the signal is recovered from the radiated wave is broadly known as demodulation or detection. It is important that the processes of modulation and demodulation be clearly understood. As already discussed, in the process of modulation the signal frequencies, which are centered about the zero-frequency reference level, are shifted upward on the...

## Fm

The primary features of a-m and f-m waves. 17-2. Instantaneous Phase and Frequency. The general expression for an unmodulated carrier wave is given by ec Ec sin (coct + 0) (17-1) In this expression the period of the wave is given by is the total instantaneous phase of the function. If the phase is written as < p(t), the value of the voltage at any instant is represented by the expression But, clearly, the angular frequency is related to the phase by the expression Fig. 17-2. The...

## Tuned Power Amplifiers

The basic circuit of a tuned power amplifier is substantially that of the single-tuned direct-coupled type discussed in Sec. 10-1. The essential differences are in the magnitude of the grid-bias supply voltage Ecc, the corresponding value of the grid input signal eg, and the amount of power involved. A schematic diagram of a tuned power amplifier is given in Fig. 11-1. Owing to the negative bias on the tube, which is adjusted approximately to plate-current cutoff in the class B amplifier and...

## The application of positive feedback has the opposite effects Thug

Positive feedback tends to sharpen the frequency-response curve and to decrease the range of uniform response. This permits an increased gain and selectivity. Positive feedback in an amplifier is critical of adjustment. Too much regenerative feedback in any system may result in oscillation. Ordinarily, negative feedback is more common than positive, feedback in amplifiers. The action of a feed-back path depends upon the frequency of operation. That is, the feedback may remain regenerative or...

## Feedback effects in an amplifier will be examined in some detail in

The basic equivalent circuit of the tetrode is essentially that of the triode, even though a screen grid exists in the tetrode. A schematic diagram of a simple amplifier circuit employing a tetrode is given in Fig. 4-6. In drawing the equivalent circuit, the rules given in Sec. 3-3 have been appropriately extended and Fig. 4-6. Schematic and equivalent circuits of a tetrode in an amplifier circuit. Fig. 4-6. Schematic and equivalent circuits of a tetrode in...

## Info

The band width of the n-stage amplifier then has the form which may be written in terms of one-stage band width as The band-width reduction factor is tabulated in Table 10-2. For a two-stage double-tuned amplifier with the coils critically coupled, the band width is 0.802 times that of the single-stage amplifier. Note that

## Electron Tube For Electrometer

The oscilloscope may be used to measure currents, although an indirect method must be adopted. In this measurement, the current to be measured is passed through a calibrated resistor, the resulting voltage across the resistor being given on the oscilloscope screen. The current may then be calculated from the known voltage and resistance. However, owing to the fact that the input impedance of the oscilloscope is only moderately high, the oscilloscope is limited to the...

## Acg

A voltage variation with respect to a definite reference potential. Fig. 7-24. A voltage variation with respect to a definite reference potential. Simple electronic circuits exist which will hold either amplitude extreme of a wave form to a given level of potential. Such circuits are known as clamping circuits and are divided roughly into two classes, continuously acting and synchronized types. The continuously acting diode and grid clamping circuits clamp either amplitude extreme...

## Untuned Voltage Amplifiers

It is frequently necessary to achieve a higher gain in an amplifier than is possible with a single stage. Amplifier stages may be cascaded to achieve this higher gain, the output voltage from one stage serving as the input voltage to the next stage. Ordinarily, however, two or three stages in cascade serving a common function is about the limit for stable opera- Fig. 5-1. Schematic diagram of a two-stage RC coupled amplifier. tion, although six- and nine-stage amplifiers are common in...

## Van Der Pol Circuit Pentode

To reduce the jitter in the trailing edge of the pulse, and also to permit somewhat greater control of pulse width with d-c bias voltage, the grid of T2 is returned to the plate supply voltage through a large grid resistor, as illustrated. Because of this change, the analysis given above must be modified. Such an analysis leads to the following expression for the discharge time of the capacitor and hence for the width of the gate Fig. 19-8. A cathode-coupled delay multivibrator. Fig. 19-9. The...

## References

Staff, Applied Electronics, Sec. 12-4 to 12-6, John Wiley & Sons, Inc., New York, 1943. Craft Laboratory, War Training Staff, Electronic Circuit and Tubes, Chap. XX, Sees. 15-18, 15-19, McGraw-Hill Book Company, Inc., New York, 1947. 1. Standards on Transmitters and Antennas, Institute of Radio Engineers, 1933. 2. Carson, J. R., Proc. IRE, 9, 243 (1921). 3. Peterson, E., and C. R. Keith, Bell System Tech. J., 7, 131 (1928). 4. Chambers, J. A., L. F. Jones, G. W. Fyler, R. H....

## Yks

The equivalent circuit of a single-tuned direct-coupled class A amplifier. Included in this diagram are the output tube capacitances C see Eq. (4-20) and the input and wiring capacitances to the following stage. The coupling capacitor may be neglected, as its capacitance is presumed to be large. In accordance with the discussion of Sec. 4-7, the gain of the amplifier can be written directly as where Z is the total load impedance. This impedance has the form where Zt is the impedance...

## Millman Theorem

The usual methods for the solution of the currents in or the potential differences across the elements of a network involve a direct application of Kirchhoff's laws. This involves setting up the mesh currents and then equating the sum of the potentials around any closed loop equal to zero. The number of independent loops that must be chosen must equal the number of unknown currents to be found. The resulting algebraic equations are then solved, ordinarily by using determinants, for the desired...

## P j eib dt p e sin e cog e

The effective resistance of the diode circuit is defined by the relation Re g s 16-26 P 9 - sin 8 cos 0 j That is, the effective resistance in parallel with the capacitor due to the loss in the diode circuit is equal to firp. A plot of is also contained in Fig. 16-6. By combining Eqs. 16-26 with 16-16 , an expression for the equivalent resistance that shunts the diode input circuit is possible. This is Re _ Re rp _ tan 6 9 R rp R 9 sin 9 cos 8 This expression is plotted as a function of R rp in...

## T

The shortcoming of these voltmeters is that the input impedance during the conducting portion of the cycle is different from that during the nonconducting portion of the cycle. This difference arises from the fact that the diode consumes power during the conducting portion of the cycle. This effect is precisely that discussed in Sec. 16-3, where it was shown that the effective input resistance to the diode Re R 2ri and is approximately R 2, where R is the load resistance. Ordinarily R is so...

## Xuz

Abnormal glow discharge, 28 Ammeters, electronic, 480 electrometer tubes, 481 Amplification, voltage see Amplifier, voltage-gain Amplification factor, measurement of, 45 numerical values for several tubes, 492 . tetrode, 23 triode, 17 Amplifier, audio-frequency, anode-follower, 108 . comparison with cathode follower, 111 gain, 109 input admittance, 110 output impedance, 109 broad-band, anode-follower see Amplifier, anode-follower cathode-follower see Amplifier, cathode-follower compensated,...

## Average Constantcurrent Characteristics

Physically, it almost entirely encloses the plate. Because of its design and disposition, the screen grid affords very complete electrostatic shielding between the plate and the control grid. This shielding is such that the grid-plate capacitance is reduced by a factor of about 1,000 or more. However, the screen mesh does not interfere appreciably with the electron flow. The reduction of the grid-plate capacitance is a very important improvement over the triode, and this matter will be...

## O

A type 852 triode has the following ratings as an r-f power amplifier and oscillator key down conditions without modulation per tube D-c plate voltage 3,000 volts D-c grid current 15 ma approx The tube is operated under rated conditions in a tuned-plate oscillator, operating at a frequency of 1 megacycle. Determine the following e. Resonant impedance of tank circuit. . Grid leak required. g. Mutual inductance between grid and plate coils. Assume that the maximum grid voltage is equal to...

## R

Owing to grid clipping, and Ecc , gt p _ Ecc Ehl on T2. must be such that eci is slightly positive and ec2 is negative. If now a positive signal is applied to both grids simultaneously, there will be no appreciable action in T1 but T2 will begin to conduct. This will reduce the grid potential on Tl, which reduces the tube current, setting off a regenerative action that continues until Tl ceases to conduct and T2 is fully conducting. The transfer is effected in precisely the same manner as that...

## Kkyv r

This expression for the gain is independent of the frequency, since no reactive elements appear in the circuit. Since each of the elements is resistive, the phase angle between input and out- Rg put voltages is constant and equal to 180 deg. L-F Region. At the low frequencies Fig. 5-5. The 1-f equivalent circuit the effect of Cg is negligible, and Yc of the RC amplifier. may be made zero. The effect of the coupling capacitor C becomes very important. The equivalent circuit under these...

## Special Sweep Generators

It may be shown that the deflection of the electron beam in an electro-magnetically deflected cathode-ray tube is proportional to the field strength of the deflecting field. The field strength is proportional to the current passing through the deflecting coil, if saturation is avoided. Consequently, if it is desired to deflect the electron beam linearly with time, the current through the coil must be increased linearly with time. When the end of the sweep is reached, the electron beam must be...

## FfTTTim

The frequency spectrum of a complex wave. 15-2. Square-law or Small-signal Modulation. Amplitude modulation may be produced by impressing two sinusoidal voltages of different frequencies in a nonlinear circuit. The van der Bijl modulator is one of the earliest methods, although it is seldom used at the present time. This modulator depends for its operation on the curvature of the transfer characteristic. A circuit of this modulator is given in Fig. 15-5. The Modulated output e Ec...

## Tuned Voltage Amplifiers

Tuned voltage amplifiers are used in those cases in which it is desired to amplify a relatively narrow band of frequencies centered about some designated mean or carrier frequency. Voltages whose frequencies lie outside of this range are undesirable and should be rejected. The use of tuned networks accomplishes this, as it is possible to adjust the tuned network so that the impedance falls steeply to low values outside of the Pig. 10-1. The three basic tuned-amplifier circuits a single-tuned,...

## L

Diode within 0.1 per cent over the range from about 8 to 150 jusec. 19-12. The Linear-sweep Delay. The linear-sweep delay circuit incorporates a feed-back linearizing circuit to achieve a linear saw-tooth wave. This particular circuit will be discussed in some detail in Chap. 20. A comparison is then effected between the potential, and hence the setting of a potentiometer, with that of any desired position on the linear saw tooth. Although the voltage comparison is accomplished in a different...

## Ek

The wave shape of the output in a simple glow-tube sweep generator. Curve a is for a supply voltage of 600 volts curve b is for a supply voltage of 135 volts. The amplitude of oscillation is the same in both cases. The amplitude of the oscillation equals the voltage difference Ed Ec. Such simple glow-tube circuits may be used for frequencies of 1 cycle every few minutes to frequencies well up in the a-f range. The wave shape of the resulting saw tooth is dependent upon the magnitude...

## Armstrong Modulator Block Diagram

E Ec sin wct cos co,, com t cos wc m 17-54 Note specifically that, if ma d,i, the only essential difference between the a-m and the p-m waves is in the relative phase of the carrier and the side bands. Evidently for small values of dd, if the side bands of the a-m wave can be shifted by 90 deg with respect to the carrier, a p-m wave results. It is immaterial, of course, whether the phase of the carrier or the phase of the side bands is shifted in order to achieve the p-m waves. The process here...

## Kbv

Frequency spectrum of a sinu-soidally modulated wave. 03C 03m, which is equal to the difference between. the carrier and the signal frequency. This component is known as the lower side band. A plot of the frequency spectrum of the modulated wave is illustrated in Fig. 15-2. It should be emphasized that the foregoing is not a mathematical fiction, as it is possible by means of appropriate filters to extract the frequencies in the spectrum. In fact, the features of transmission of...

## Ufo

Typical wave form of the suppressor voltage in a pentode van der Pol relaxation oscillator. Fig. 18-24. Typical wave form of the suppressor voltage in a pentode van der Pol relaxation oscillator. flows in the screen circuit. The capacitor charging current now flows through R3 and the combination of R2 in parallel with the screen-cathode path resistance, and the potential of the suppressor begins to rise. This brings the action to the point at which the considerations began, and the...

## Problems

Eb of the 6H6 diode see Appendix B on log paper. From this plot determine the quantities k and n in the expression lb kE . 2-2. The anode current in a type 5U4G diode with 54 volts applied between the plate and cathode is 200 ma. What is the required potential for a current of 100 ma The tube operates under space-charge conditions. 2-3. Suppose that the FP-400 tube is operating under rated filament power input see Prob. 1-2 . The operating temperature is 2700CK anode diameter...

## Fwo

Capacitance, interelectrode, numerical values for several tubes, 492 . pentodes, 63 tetrodes, 62 triodes, 58 Capacitor filters see Filter, rectifier, capacitor Carrier suppression, 325 Carrier wave, disappearance of, in frequency modulation, 369 suppression of, 325 Cathode, directly heated, 4 indirectly heated, 4 inward-radiating, 4 mercury as, 28 oxide-coated, disintegration, 31 emission, 3 work function, 3 photoelectric, 4 power for heating, 64 thermionic see Thermionic cathodes Thermionic...

## Untuned Power Amplifiers

The voltage amplifiers discussed in Chaps. 5 and 6 are designed to increase a voltage signal from a low level to one which is adequate for operating some low-power circuit. Such amplifiers are generally operated in class A since the amplification is to be accomplished without distortion. Pig. 9-1. The schematic and equivalent circuits of a simple series-fed power amplifier. Pig. 9-1. The schematic and equivalent circuits of a simple series-fed power amplifier. A power amplifier serves to supply...

## Fpw

For a circuit for which the linear time is to extend for 100 sec, the deviation becomes The initial potential drop that appears in the plate potential does not appear in these equations but represents the contribution to the initial plate current by the charging current required to charge the tube and wiring capacitances. If the circuit is modified as illustrated in Fig. 19-26, a control is possible to the upper and lower potential limits between which the linear saw tooth traverses. In this...

## Gas Tubes

There are two important types of discharge in gases that play roles in electron tubes. One of these is the glow discharge, and the second is the arc discharge. The glow discharge utilizes a cold cathode and is characterized by a fairly high tube drop and a low-current-carrying capacity. The voltage drop across the tube over the operating range is fairly constant and independent of the current. The arc discharge is characterized by a low voltage drop and a...

## Current Generator Circuit For A Pentode

The output-voltage wave form from biased saw-tooth generator. the sweep generator of Fig. 20-13. If the tube is normally biased negatively so that no current flows through it, then upon the application of a positive gate the potential across the capacitor will fall from the value Ebb to the value determined by the drop across the tube Eb and the drop across the resistor Ri2, if one is used to limit the current through the tube. The generator circuit is given...

## E volts Ea volts C if R ohms

Calculate the frequency of oscillation. b. Calculate the amplitude of the generated waves. c. Plot the wave shape of the generated waves. Assume that the flyback time is zero. 20-2. Design a thyratron relaxation saw-tooth generator to yield a substantially linear saw tooth having a peak amplitude of 25 volts, with a recurrence frequency of 1,000 cps. Specify reasonable values of Ebb, Ecc, R and C, and give reasons for your choice. 20-3. Derive an equation for the potential across capacitor C...

## S

A simple voltage-regulator circuit. ally such special tubes are not necessary, as it is quite possible to achieve the same ends by including a d-c amplifier in the circuit in such a way that slight changes in output potential are amplified before being applied degeneratively to T. These circuits are used extensively and a detailed analysis will be given below. 14-9. Electronic Voltage Regulators Basic Considerations. The design of electronically regulated power supplies has become...

## Comparison Of The Cathode And Anode Follower

Direct-coupled Amplifier.4 It is possible to build a type of cascaded amplifier without reactive elements and, in principle at least, secure a very broad band amplifier. The voltage gain of such an amplifier does not depend on the frequency, at least to a first approximation, except for the effect of tube and wiring capacitances at the higher frequencies. It might appear that such amplifiers would find very widespread use because of these desirable characteristics. However, such amplifiers...

## Bid

It follows from this that the required LC product for a specified ripple r is given by Note also that, to the approximation that the impedance between A 2 and B2 is simply Xc , the critical inductance is giyen by Eq. 14-37 , as for the single-section unit. 14-6. Il-section Filter. The use of a II-section filter provides an output potential that approaches the peak value of the a-c potential of the source, the ripple components being very small. Such a filter is illustrated in Fig. 14-15....