Problems

1. A modulated amplifier that is operated in class C with the modulating signal injected into the plate circuit has an unmodulated carrier output of 5.0 kilowatts. With 100 per cent sinusoidal modulation, what is the approximate direct power drawn by the plate circuit, the approximate alternating power drawn from the modulating amplifier, the approximate direct power drawn by the modulating amplifier, and the approximate total 60-cycle alternating power drawn by the transmitter.

2. If the power-output tubes of a transmitter should work at 1825 kilocycles into 3250 ohms resistance and if the input impedance to the transmission line is 175 ohms resistance, design a simple impedance-matching network for coupling the transmitter to the line. Repeat if the line impedance is 1250 ohms resistance.

3. In the system of Fig. 7, the standing-wave ratio is 4.7 without the stub. If the frequency is 59.75 megacycles, determine the lengths and locations of open and shorted stubs to remove the standing waves. Is it possible to substitute for the open stub a shorted stub that is λ/4 longer than the open stub? Why?

4. The length of the antenna in Fig. 9 is 0.5 V The feeders are of No. 10 wire, 8 inches apart. Two copper tubes of outside diameter 1.1 inch are available. Can they be used to approximately match the impedances? If so, what spacing must they have? If not, what is a suggested diameter?

5. A vertical broadcast antenna with a base insulator is fed by an underground coaxial cable. What lightning protection would you recommend? If the tower is struck, can the transmitter cause a radio-frequency power arc on the system? If so, where will it probably occur?

6. The functioning of the l.0-megohm resistor and 150-micromicrofarad capacitor of Fig. 14 is explained on page 501. Assume that the station being received is modulated with a 1000-cycle tone and that the circuit is in a typical superheterodyne and calculate the impedance offered to the principal alternating components that will be impressed on this parallel combination.

7. In discussing Fig. 26 it is explained that sometimes the capacitor between the primary and the secondary is omitted and a coil is used. Assume that this change and other necessary modifications have been made and draw the required vectors. Prepare a discussion to explain the operation of the circuit.

8. On page 525 the statement is made that the frequency multipliers increase both the frequency and the frequency deviation. Prove this to be true.