ANSWERS TO EXERCISES [AM-FM Broadcasting Equipment, Operations, and Maintenance (1974)]

Home | Audio Magazine | Stereo Review magazine | Good Sound | Troubleshooting


A1-1. (A) The rf carrier is increased and decreased in amplitude by the applied signal. (B) The rf carrier remains constant in amplitude, but the frequency is varied by the applied signal.

A1-2. 535 kHz to 1605 kHz.

A1-3. Lowest: 540 kHz. Highest: 1600 kHz.

A1-4. (A) Lower sideband = 880 kHz. (B) Upper sideband = 900 kHz.

A1-5. (A) Minimum, 10 kW; maximum, 50 kW.

(B) Minimum, 250 watts; maximum, 250 watts nighttime, 1 kW daytime.

A1-6. 88 to 108 MHz.

A1-7. 200 kHz.

A1-8. Antenna height (Review Section 1-4) .

A1-9. The pilot subcarrier is used in stereophonic fm broadcasting as a control signal for fm stereo receivers.

Al-10. 23 to 53 kHz.



A2-1. 4 7 8-10 9- 6 28-16 28- 16 = 12 (Answer) A2-2. 21 5-30 2-16 28-46

-46 + 28 =-18 (Answer) A2-3. 5-(-16)=21 A2-4. (4/5) (3) = 12/5 A2-5. 9/3 3 32 32 or:

9 3 32(3) 96 32 A2-6. 1/7 + 1/3 + 1/2 = 6/42 + 14/42 + 21/42 = 41/42 A2-7. 1/4- 1/6 = 3/12- 2/12 = 1/12 A2-8. (2/3) (1/5 ) = 2/15 A2-9. (3/4) (6/10) = 18/40 =9/20 A2-10. 2/3- 3/5 = (2/3)(5/3) = 10/9 = 19 A2-11. 30/4- 15/3 + 180- 5

= 7.5- 5 + 180- 5

= 187.5- 5- 5

= 187.5- 10 = 177.5

A2-12.48- 47.5 (100) 47.5

0.5 475(100)

= 0.0105(100) = 1.05% A2-13. 100 = 1 40 = 1 20 = 1 A2-14. 5-8 A2-15. (A) 415 (B) 415 (C) 4-15 (D) 4-12 A2-16. 9/16 A2-17. V6'95'73 Step 1 2 V6'95'73 Step 2 4 2 95 2 6

.V 6'95'73 4 46 )2 95 2 76 1973 2 6 3 V 6'95'73 4 46 ) 2 95 523 ) 19 73 15 69 4 04 Remainder So: V69,573 = 263 Step 3 Step 4

(4)(5)(2)103-12+6 A218.

(5)(4)(1016-7) 40(10-3) 20(109) 2(10-3)

=2(10-12) 109 A2-19. (A) 3 (B) 2 (C) 1 (D) 0 (E)-4 A2-20. 1.7376 A2-21. Log 1.24 = 0.0934 Log 246 = 2.3909 Total = 2.4843 Antilog 2.4843 = 305 (Answer) A2-22. Log 961 = 2.9827 Log 224 = 2.3502 Difference = 0.6325 Antilog 0.6325 = 4.29 (Answer) A2-23. Log 638 = 2.8048 Exponent = 5 Product = 14.0240 Antilog 14.024 = 1.057(1014) (Answer) A2-24. B = X/A A=X/B A2-25. R = 14.54 r = 39°54' The resultant is 14.54 /39°54' A2-26. 20 /30° = 20(cos 30° + j sin 30°)


= 17.32 + j10 A2-27. V'302 + 502

=V 900 + 2500

= V3400 = 58.3 tan r = 50/30 =

Then r = 59°02' Complete answer:

(Magnitude) 1.6667 (Approx ) 58.3 /59°02' A2-28. 1 milliwatt (mW) in 600 ohms.

A2-29. 100/150 = 0.66 = 1.8 dB loss.

A2-30. 104 SECTION 3 A3-1. The R1-R2 voltage divider gives a voltage of 3 volts at the Q1 base.

See Fig. B-1; this is the dc equivalent circuit. Note that the feedback shown in this diagram is dc feedback only; C2 and R4 provide a by pass around R6 to frequencies in the passband. Coupling capacitors C1 and C3 prevent the dc operating point from being influenced by source and load characteristics.

Since the voltage at the base of Q1 is 3 volts, VE of Q1 is +3- 0.6

= 2.4 volts. The current through R6 to produce this 2.4 volts is 2.4/1000 = 2.4 mA.

At Q2 there will be a 0.6-volt difference between emitter and base, so VB of Q2 = 6- 0.6 = 5.4 volts. This is also the voltage at the collector of Q1. The current through R3 to drop 0.6 volt is 0.6/1000

= 0.6 mA, and almost all of this current goes to the Q1 collector. The emitter current of Q1 will also be about 0.6 mA.

Fig. B-1. Dc equivalent of Fig. 3-69.

The current through R6 is 2.4 mA. Since 0.6 mA of this current comes from the emitter of Q1, 2.4- 0.6 = 1.8 mA must come through R5. The voltage drop across R5 is then (1.8) (1) = 1.8 volts.

The voltage at the collector of Q2 is the sum of the voltage drops across R5 and R6, or 2.4 1.8 = 4.2 volts.

A3-2. (A) Positional Weight-' 16 8 4 2 1 Binary-> 1 0 0 0 0

= 10000.00 binary (B) Bcd = 0001 0110

= 1 6 = decimal 16 (C) Binary 010000 2 0

= 20 octal A3-3. (A) 1011. (B) 13.

A3-4. (A) 1000111000. (B) 1070.

A3-5. 41.25 A3-6. (A) A and B. (B) A or B.

A3-7. (A) Diode-transistor logic. (B) Resistor-transistor logic. (C) Resistor-

capacitor-transistor logic. (D) Transistor-transistor logic.

A3-8. See Fig. B-2. Note that the truth table starts with binary number zero (0000) and increases by adding 1 each time until the number 15 (1111) is reached. This assures that no combination is omitted.

A3-9. See Fig. B-3.

A3-10. See Fig. B-4.

A3-11. No. A reset pulse can be made to coincide with the binary equivalent of an odd number, restarting the count to obtain division by an odd integer.

SECTION 4 A4-1. Only at the expense of frequency discrimination (Fig. 4-13).

A4-2. A "figure eight" pattern.

Fig. B-2. Truth table for AND portion of Fig. 3-52A.

A4-3. Three. One terminal is common. The left and common feed the left channel. The right and common feed the right channel.

A4-4. Yes. The left and right terminals are paralleled to feed a single channel.

A4-5. Single.

Fig. B-3. Truth table for OR portion of Fig. 3-52A.

Fig. B-4. Truth table for NOT portion of Fig. 3-52A.

A4-6. 0.25 inch. (Actually 0.246 plus or minus 0.002 in.) A4-7. 0.24 inch.

A4-8. Track width is 80 mils plus slight "spill over" at edges. Center-to-

center spacing is 160 mils.

A4-9. Track width = 37 mils. Center-to-center track spacing = 71 mils.

A4-10. To compensate for the nonlinear B-H curve of the magnetic tape.

SECTION 5 A5-1. No. Practically all tape cartridge systems require an external bulk eraser to erase the tape. Also, some very-slow-speed reel-to-reel recorders, such as those used for logging, do not have an erase head.

A5-2. No. It supplies only sufficient torque to maintain correct tape tension between the capstan and take-up reel.

A5-3. The capstan motor and pinch-roller assembly.

A5-4. 33/a and 71/2 in/s.

A5-5. As the frequency is decreased, the magnetic field energy decreases at a 6 dB/octave rate and falls into the noise level.

A5-6. 71/2 in/s.

A5-7. (A) 1000 Hz. (B) 150 Hz. (C) 8000 Hz.

A5-8. The lower track of a monophonic system, and the lowest track of a three-track stereo system.

A5-9. Left channel: upper track. Right channel: middle track.

A5-10. So that the proper speed is established prior to the instant at which the capstan pinch roller engages the tape.

SECTION 6 A6-1. The balanced circuit requires an H pad.

Attenuation required = 32 dB.

Refer to Fig. 6-6B for configuration. From Table 6-2:

K1 = 0.950 K2 = 19.8 R1 = (600 + 150) (0.950) + (600- 150) 2 1162 =581 ohms R2 = (600 + 150) (0.950)- (600- 150) 2 262 131 ohms 2 R3 = 600 + 150 750 18.9 ohms (2) (19.8) 39.6 Final solution:

R1 291 ohms (nearest EIA value = 300 ohms) 2 R2 65.5 ohms (nearest EIA value = 68 ohms) 2 R3 = 18.9 ohms (nearest EIA value = 18 ohms) A6-2. The loss when the attenuator is placed fully clockwise (maximum volume) .

A6-3. 6 dB.

A6-4. Zero insertion loss in both cases when operated between like impedances.

A6-5. The output level required for a s/n ratio of 60 dB is-80 + 60

=-20 dBm. Since the gain of the amplifier is 40 dB, then the input level required for a-20-dBm output is-20 + (-40) =-60 dBm.

A6-6. (A) Max input level = +18- 40 =-22 dBm (B) s/n ratio = +18- (-80) = 98 dB

A6-7. The required attenuation is 25 dB. From Table 6-3, R1 = 5000 ohms and R1- 2500 ohms. Two 300-ohm resistors are added across the amplifier input terminals with the center junction of the resistors grounded (see the balanced-configuration diagram in Table 6-3).

Note that this bridging impedance precludes adding any further bridging circuits to this line.

A6-8. (A) R = 3Re .=450 = 90 ohms (B) Min loss = 20 log 4

_ (20) (0.602)

= 12 dB

Therefore the amplifier input level is-72 dBm if the microphone delivers-60 dBm.

A6-9. With a-72-dBm input and a gain of 40 dB, the output level is-32 dBm. Then the s/n ratio is 80- 32 = 48 dB.

A6-10. 8/4 = 2 watts for each speaker.

SECTION 7 A7-1. The color coding of the lead that is "positive" relative to the other leads. The positive wire of each microphone must have the same connection to corresponding terminals of the preamplifiers. This is true for either stereo or mono broadcasting.

A7-2. Ambient sound versus direct sound.

A7-3. If only quad discs are used, no further encoding is necessary. If four microphones or four-track (four-head) tape is employed, encoding is necessary.

A7-4. It converts the original four-channel sound to two channels in such a manner that the original four channels can be separated by a de coding device.

A7-5. Left and right speakers reproducing the same magnitude of in-phase signal. For quad sound, this applies only to the left-front and right-

front speakers.

A7-6. No.

A7-7. Yes.

A7-8. Yes.

A7-9. No.

SECTION 8 A8-1. 947-952 MHz.

A8-2. Yes. For remote-pickup and mobile service, see Chart 8-1.

For STL's, see answer A8-1.

A8-3. 0.6 of the first-Fresnel-zone radius.

A8-4. Path of most concentrated energy bounded by a path where an additional half-wavelength in the path length causes phase cancellation.

A8-5. Because of strong reflections from a smooth surface.

A8-6. Fm.

A8-7. Coaxial cable.

A8-8. (A) 50 dB (B) 60 dB SECTION 9 A9-1. The angle subtended by a section of the circumference a circle equal in length to the radius of that circle. Mathematically:

1 Radian = 180°- 57.32° pi A9-2. Radians = ( Degrees) ( ) 180° A9-3. pi radians, or 3.14.

A9-4. (A) 500 meters, or 1640 feet. (B) 187.5 meters, or 615 feet.

A9-5. Ground-wave signals.

A9-6. 10 mV/m.

A9-7. The class-C stage used to amplify carrier power (unmodulated) em ploys high-Q (narrow-band) tuned amplifiers for the carrier frequency. The linear rf amplifier must have a bandwidth to include all sideband frequencies, which calls for lower-Q tuned circuits.

A9-8. 22.5 percent over the unmodulated value of antenna current.

A9-9. 85 percent (approximately).

A9-10. (A) 15 kW.

(B) 11.25 kW.

(C) 10.3125 kW.

SECTION 10 410-1. Almost directly proportional to the number of stacked bays. See Table 10-2.

A10-2. (A) 10 log 6 = (10) (0.7782) = 7.78 dB (B) \/6=2.44 410-3. Approximately proportional to the number of bays divided by 2.

See Table 10-4.

A10-4. (A) Amplitude. (B) Amplitude and frequency.

A10-5. The frequency response (after pre-emphasis) is made proportional to the reciprocal of the modulating frequency (1/f.).

A10-6. Same as modulation index. (A) 5. (B) 3750.

410-7. (A) 1 radian = 57.3°, so (5) (57.3) = 286.5° (B) (3750) (57.3) = 215,000° (approx) A10-8. ±75 kHz/4 = ±18.75 kHz A10-9. Frequency modulated.

A10-10. Amplitude modulated.

A10-11. L- R, suppressed carrier.

A10-12. 23 kHz to 53 kHz.


A11-1. The hearing sense is not "flat." (Review Figs. 2-16 and 11-5, with associated text.) This simply emphasizes that if the operator groups performers around a microphone so that lows and highs are in balance with a "flat" monitoring system, a flat frequency response in the remainder of the system is desirable. Bass and treble controls in the receiver compensate for room acoustics and individual listener preference.

A11-2. The compression meter, which shows the amount of compression or limiting taking place.

A11-3. Around 32 percent, or about-10 dB from program peaks.

A11-4. In practice, three basic types: (A) acoustical, Fig. 11-11; (B) magnetic tape, Figs. 11-12 and 11-13; and (C) electro-sonic delay lines.

The latter type is encountered often in professional recording studios but very seldom in broadcast installations.

A11-5. Position the piano so that the keyboard hammer line is more on axis to the microphone, keeping the same distance.

A11-6. Use the minimum number possible for adequate coverage. Reposition performers around one microphone if possible to obtain balance.

A11-7. The FCC says the station licensee. In the final analysis, the operator on duty has control over "loudness."


A12-1. Remote programs require more microphones to accentuate the ratio of direct to reflected sound and to prevent the ambient noise level from destroying the program.

A12-2. Use an isolation coil as shown in Fig. 12-3. Use the balanced-line side of the transformer for the line, with 10K bridging resistors in each side. Connect the public-address input to the unbalanced side of the transformer. The pa amplifier normally has sufficient gain to allow this bridging. It may be necessary to use the microphone input on the pa amplifier.

A12-3. Many remote amplifiers have an adjustable multiplier for the VU meter, allowing zero reference to be +4, +8, or +12 VU. Use the highest level possible (such as +12) for the amplifier feeding the program line. This normally overrides such interference.

A12-4. Use of an equalizer at the studio will normally provide satisfactory quality for voice (only) transmission.


A13-1. Place a 47K resistor in series with the vom, and take this into account in the reading.

A13-2. A broken shield or ground wire.

A13-3. No. The playback response should be the inverse of the recording characteristic.

A13-4. Be sure the IC leads are not folded against the board on the soldered side. Otherwise, damage to the board will result.

A13-5. Clean and demagnetize the heads.

A13-6. Head-to-tape contact, tilt, height, tangency, azimuth.

A13-7. Yes. See Section 13-9.

A13-8. All transmitters and receivers in the same system are tuned to the same frequency.

A13-9. Total harmonic distortion (thd).

A13-10. Be sure to use an input signal which is below the maximum input rating of the amplifier into which the signal is inserted.


A14-1. No. The VU meter has a full-wave rectifier and a specially damped movement. The modulation meter is a device to measure either negative or positive modulation at a given time, and it is a semi-peak device rather than rms.

A14-2. The bridge method and the substitution method. Details are covered in Section 14-4.

A14-3. By the direct method.

A14-4. (A) Antenna current squared times antenna impedance.

(B) EXIXF where, E is the plate voltage of the final stage, I is the plate current of the final stage, F is an efficiency factor furnished by the manufacturer.

A14-5. If used, the limiting or agc action must be removed.


The relationship provides identification of the left and right channels. If the second harmonic should cross the time axis with a negative slope at the transmitter and a positive slope at the receiver, the "left channel as transmitted would be reproduced in the "right channel of the receiver, and conversely.

A14-7. It maintains the relationship of the left-plus-right signal to the left-

minus-right signal. If this standard varied from station to station (deviation upward in some transmitters and downward in others), the left and right channels would be reversed in the receiver, de pending on the station being received.

A14-8. Paragraphs L and M give the FCC requirements for channel separation. Paragraph L specifies the required amplitude response of the two channels, and paragraph M specifies the phase response. With a steady-state signal in the left channel only, signals of the same frequency and equal amplitudes (within 31/2 percent) exist in the left-plus-right and left-minus-right channels. The phase difference between the left-plus-right and left-minus-right signals must not exceed i-3° between 50 Hz and 15 kHz.

The above may be summarized by stating that for proper channel separation, the left-plus-right and left-minus-right channels must have the same frequency response, and all frequencies in both channels must arrive at the receiving matrix at the same time (in the proper phase relationship) .

The FCC note following paragraph M specifies when further measurements in checking channel separation are required. For a given signal in the left channel only, adjustment is satisfactory if the signal recovered at the receiver (or receiver-type monitor) in the right channel is attenuated at least 29.7 dB. This must be true throughout the frequency range of 50 Hz to 15 kHz. If this check is negative, further measurements of the frequency and phase response must be taken.

A14-9. No. Paragraphs N and O of the standards specify transmitter requirements in checking channel separation with respect to cross talk from the left-minus-right channel into the left-plus-right channel (stereo subchannel into main channel) and cross talk from the left-plus-right channel into the left-minus-right channel (main channel into stereo subchannel) .

A14-10. The modulation meter. See Section 14-12.

Prev. |

Top of Page  | Index |  Home

Updated: Tuesday, 2021-09-14 21:48 PST