TRUE/FALSE
1. The first radio receiver was built in 1918.
ANS: F
2. Almost all modern receivers use the superheterodyne design.
ANS: T
3. A tuned circuit at the input increases receiver sensitivity.
ANS: F
4. Since both fo and Q increase with frequency, the bandwidth of a resonant LC circuit remains constant as it is tuned to higher frequencies.
ANS: F
5. The resistance of a coil is a function of frequency.
ANS: T
6. The superhet was invented by Heinrich Hertz.
ANS: F
7. In a receiver, the first RF amplifier is largely responsible for overall noise performance.
ANS: T
8. In a superhet, the local oscillator must be set to the transmitter's carrier frequency.
ANS: F
9. In a superhet, the output of the mixer is the IF.
ANS: T
10. In a superhet, most of the gain comes from the IF amplifiers.
ANS: T
11. In a superhet, most of the selectivity comes from the IF amplifiers.
ANS: T
12. All superhets use a separate local oscillator.
ANS: F
13. In high-side injection, the incoming RF is at a higher frequency than the local oscillator.
ANS: F
14. The mixer and the local oscillator can use the same transistor.
ANS: T
15. The IF frequency is constant as a receiver is tuned to various frequencies.
ANS: T
16. There can be only one mixer and one IF in a superhet receiver.
ANS: F
17. In AM receivers, the antenna and the inductor of the tuner circuit can be the same thing.
ANS: T
18. Bandwidth and signal-to-noise-ratio are not related in a superhet.
ANS: F
19. Shape-factor is a measure of selectivity.
ANS: T
20. Phase distortion should be minimized for reliable voice communications.
ANS: F
21. A receiver's response to weak signals is limited by the noise generated inside the receiver.
ANS: T
22. The AGC in a receiver can cause "blocking".
ANS: T
23. Careful design can eliminate all spurious responses.
ANS: F
24. Image frequencies are eliminated by the IF.
ANS: F
25. "Software radios" use a DSP to replace all hardware up to and including the detector.
ANS: F
26. It is possible that a transmitter on one frequency can appear at two spots on a receiver's dial.
ANS: T
27. A detector is the same as a demodulator.
ANS: T
28. Envelope detectors are typically used in FM receivers.
ANS: F
29. Envelope detectors are complicated, but extremely linear.
ANS: F
30. There is a way to use a diode to demodulate a SSB signal.
ANS: T
31. A SSB signal requires a ratio detector.
ANS: F
32. In a SSB receiver, the BFO injects the carrier into the detector.
ANS: T
33. In a SSB receiver, it is relatively easy for the injected carrier to match the frequency and phase of the transmitter's carrier.
ANS: F
34. If the BFO in a SSB receiver is 100 hertz low, what comes out of the speaker may sound like Donald Duck, but it will be understandable.
ANS: T
35. DSBSC transmitters often use a pilot carrier to allow coherent detection.
ANS: T
36. FM receivers are similar to AM receivers in basic design.
ANS: T
37. There is no way to demodulate an FM signal with an AM receiver.
ANS: F
38. Modern FM receivers commonly use Foster-Seeley discriminators.
ANS: F
39. Both PLLs and quadrature detectors can be used to demodulate FM.
ANS: T
40. Quadrature detectors are sensitive to variations in carrier amplitude.
ANS: T
41. Squelch is the same as muting.
ANS: T
42. A bipolar transistor can be used as a mixer, but a FET cannot.
ANS: F
MULTIPLE CHOICE
1. The two basic specifications for a receiver are:
| a. | the sensitivity and the selectivity |
| b. | the number of converters and the number of IFs |
| c. | the spurious response and the tracking |
| d. | the signal and the noise |
ANS: A
2. The superheterodyne receiver was invented by:
| a. | Foster | c. | Armstrong |
| b. | Seeley | d. | Hertz |
ANS: C
3. Trimmers and padders are:
| a. | two types of adjusting tools | c. | small adjustable inductors |
| b. | small adjustable resistors | d. | small adjustable capacitors |
ANS: D
4. "Skin effect" refers to:
| a. | the way radio signals travel across a flat surface |
| b. | the tissue-burning effect of a strong RF signal |
| c. | the increase of wire resistance with frequency |
| d. | none of the above |
ANS: C
5. The "front end" of a receiver can include:
| a. | the tuner | c. | the mixer |
| b. | the RF amplifier | d. | all of the above |
ANS: D
6. "IF" stands for:
| a. | intermediate frequency | c. | indeterminate frequency |
| b. | intermodulation frequency | d. | image frequency |
ANS: A
7. AGC stands for:
| a. | Audio Gain Control | c. | Active Gain Control |
| b. | Automatic Gain Control | d. | Active Gain Conversion |
ANS: B
8. The frequency of the local oscillator:
| a. | is above the RF frequency |
| b. | is below the RF frequency |
| c. | can be either above of below the RF frequency |
| d. | is fixed, typically at 455 kHz. |
ANS: C
9. The local oscillator and mixer are combined in one device because:
| a. | it gives a greater reduction of spurious responses |
| b. | it increases sensitivity |
| c. | it increases selectivity |
| d. | it is cheaper |
ANS: D
10. Basically, sensitivity measures:
| a. | the weakest signal that can be usefully received |
| b. | the highest-frequency signal that can be usefully received |
| c. | the dynamic range of the audio amplifier |
| d. | none of the above |
ANS: A
11. Basically, selectivity measures:
| a. | the range of frequencies that the receiver can select |
| b. | with two signals close in frequency, the ability to receive one and reject the other |
| c. | how well adjacent frequencies are separated by the demodulator |
| d. | how well the adjacent frequencies are separated in the mixer |
ANS: B
12. When comparing values for shape factor:
| a. | a value of 1.414 dB is ideal | c. | a value of 1.0 is ideal |
| b. | a value of 0.707 is ideal | d. | there is no ideal value |
ANS: C
13. When comparing values for shape factor:
| a. | a value of 2 is better than a value of 4 | c. | both values are basically equivalent |
| b. | a value of 4 is better than a value of 2 | d. | none of the above |
ANS: A
14. Distortion in a receiver can occur in:
| a. | the mixer | c. | the IF amplifiers |
| b. | the detector | d. | all of the above |
ANS: D
15. Phase distortion is important in:
| a. | voice communications systems | c. | monochrome video receivers |
| b. | color video receivers | d. | all of the above |
ANS: B
16. The response of a receiver to weak signals is usually limited by:
| a. | the AGC | c. | the dynamic range of the receiver |
| b. | noise generated in the receiver | d. | the type of detector circuit being used |
ANS: B
17. Image frequencies occur when two signals:
| a. | are transmitted on the same frequency |
| b. | enter the mixer, with one being a reflected signal equal to the IF frequency |
| c. | enter the mixer, one below and one above the local oscillator by a difference equal to the IF |
| d. | enter the mixer, and the difference between the two signals is equal to twice the IF |
ANS: C
18. An image must be rejected:
| a. | prior to mixing | c. | prior to detection |
| b. | prior to IF amplification | d. | images cannot be rejected |
ANS: A
19. Image frequency problems would be reduced by:
| a. | having an IF amplifier with the proper shape factor |
| b. | having a wideband RF amplifier after the mixer |
| c. | having a narrowband RF amplifier before the mixer |
| d. | none of the above |
ANS: C
20. A common AM detector is the:
| a. | PLL | c. | ratio detector |
| b. | envelope detector | d. | all of the above |
ANS: B
21. An FM detector is the:
| a. | PLL | c. | quadrature detector |
| b. | ratio detector | d. | all of the above |
ANS: D
22. Germanium diodes are used in AM detectors because:
| a. | they are faster than silicon diodes |
| b. | they are cheaper than silicon diodes |
| c. | they minimize distortion from nonlinearity |
| d. | all of the above |
ANS: C
23. A common SSB detector is:
| a. | a PLL | c. | a BFO |
| b. | a diode | d. | a product detector |
ANS: D
24. BFO stands for:
| a. | Beat Frequency Oscillator | c. | Bipolar Frequency Oscillator |
| b. | Barrier Frequency Oscillator | d. | Bistable Frequency Oscillator |
ANS: A
25. To demodulate both SSB and DSBSC, you need to:
| a. | use a Foster-Seeley discriminator |
| b. | reinject the carrier |
| c. | use double conversion |
| d. | use one diode for SSB and two diodes for DSBSC |
ANS: B
26. Which would be best for DSBSC:
| a. | carrier detection | c. | envelope detection |
| b. | coherent detection | d. | ratio detection |
ANS: B
27. An FM detector that is not sensitive to amplitude variations is:
| a. | Foster-Seeley detector | c. | a PLL detector |
| b. | a quadrature detector | d. | all of the above |
ANS: C
28. The function of a limiter is:
| a. | to remove amplitude variations | c. | to limit dynamic range |
| b. | to limit spurious responses | d. | to limit noise response |
ANS: A
29. Suppressing the audio when no signal is present is called:
| a. | AGC | c. | AFC |
| b. | squelch | d. | limiting |
ANS: B
30. LNA stands for:
| a. | Limited-Noise Amplifier | c. | Low-Noise Audio |
| b. | Low-Noise Amplifier | d. | Logarithmic Noise Amplification |
ANS: B
31. AFC stands for:
| a. | Audio Frequency Compensator | c. | Automatic Frequency Control |
| b. | Autodyne Frequency Compensation | d. | Autonomous Frequency Control |
ANS: C
32. The function of AFC is:
| a. | maintain a constant IF frequency |
| b. | match the local oscillator to the received signal |
| c. | lock the discriminator to the IF frequency |
| d. | none of the above |
ANS: B
33. SAW stands for:
| a. | Symmetrical Audio Wave | c. | Silicon-Activated Wafer |
| b. | Surface Acoustic Wave | d. | Software-Activated Wave |
ANS: B
34. The important property of a SAW is:
| a. | it stabilizes the audio in a receiver | c. | it is a stable bandpass filter |
| b. | it allows software radios to be built | d. | none of the above |
ANS: C
35. The main function of the AGC is to:
| a. | keep the gain of the receiver constant |
| b. | keep the gain of the IF amplifiers constant |
| c. | keep the input to the detector at a constant amplitude |
| d. | all of the above |
ANS: C
36. DSP stands for:
| a. | Dynamic Signal Properties | c. | Distorted Signal Packet |
| b. | Direct Signal Phase | d. | Digital Signal Processor |
ANS: D
37. SINAD stands for:
| a. | Sinusoidal Amplitude Distortion |
| b. | Signal and Noise Amplitude Distortion |
| c. | Signal-plus-Noise-to-Noise Ratio |
| d. | Signal-plus-Noise and Distortion-to-Noise and Distortion Ratio |
ANS: D
38. TRF stands for:
| a. | Tuned Radio Frequency | c. | Transmitted Radio Frequency |
| b. | Tracking Radio Frequency | d. | Tuned Receiver Function |
ANS: A
COMPLETION
1. Almost all modern receivers use the _________________________ principle.
ANS: superheterodyne
2. The first radio receiver of any kind was built in the year ____________________.
ANS: 1887
3. When two tuned circuits ____________________ each other, it means that when the frequency of one is adjusted, the other changes with it.
ANS: track
4. The ____________________ effect causes the resistance of wire to increase with frequency.
ANS: skin
5. The superhet was invented in the year ____________________.
ANS: 1918
6. In a receiver, the ____________________ refers to the input filter and RF stage.
ANS: front end
7. In a superhet, the output of the ____________________ goes to the IF amplifiers.
ANS: mixer
8. In a superhet, the ____________________ frequency is the difference between the local oscillator frequency and the received signal frequency.
ANS:
intermediate
IF
9. The ____________________ circuit adjusts the gain of the IF amplifiers in response to signal strength.
ANS: AGC
10. An ____________________ converter uses the same transistor for both the local oscillator and the mixer.
ANS: autodyne
11. In low-side injection, the local oscillator is ____________________ than the received signal frequency.
ANS: lower
12. ____________________ is the ability of a receiver to separate two signals that are close to each other in frequency.
ANS: Selectivity
13. ____________________ is the ability of a receiver to receive and successfully demodulate a very weak signal.
ANS: Sensitivity
14. A receiver with two different IF frequencies is called a double-____________________ receiver.
ANS: conversion
15. A multiple-conversion receiver will have better rejection of ____________________ frequencies.
ANS: image
16. A demodulator is also called a ____________________.
ANS: detector
17. An ____________________ detector uses a diode to half-wave rectify an AM signal.
ANS: envelope
18. A ____________________ detector is used for SSB signals.
ANS: product
19. A BFO produces a locally generated ____________________.
ANS: carrier
20. A DSBSC signal requires a ____________________ detection circuit.
ANS: coherent
21. FM detectors have a characteristic ____________________-shaped curve.
ANS: S
22. While still commonly found, the Foster-Seeley and ratio detectors are ____________________.
ANS: obsolescent
23. Unlike the PLL detector, the quadrature detector is sensitive to changes in ____________________ of the input signal.
ANS: amplitude
24. A dual-____________________ MOSFET is useful for AGC.
ANS: gate
25. Diode mixers are too ____________________ to be practical in most applications.
ANS: noisy
26. The IF amplifiers in an AM receiver must be Class ____________________.
ANS: A
27. A double-tuned IF transformer is usually ____________________ coupled for the response to have a flat top and steep sides.
ANS: over
28. Multiple IF stages can be ____________________-tuned to increase the bandwidth.
ANS: stagger
29. Compared to tuned circuits, ceramic and crystal IF filters do not require ____________________.
ANS: adjustment
30. Up-conversion is when the output of the mixer is a ____________________ frequency than the incoming signal.
ANS: higher
31. In a block converter, the frequency of the first local oscillator is ____________________.
ANS:
fixed
constant
32. Typically, AGC reduces the gain of the ____________________ amplifiers.
ANS: IF
33. An ____________________-meter is designed to indicate signal strength in many communications receivers.
ANS: S
34. The effectiveness of FM ____________________ is measured by a receiver’s quieting sensitivity.
ANS: limiting
35. A ____________________ refers to any kind of FM or PM detector.
ANS: discriminator
SHORT ANSWER
1. Suppose the bandwidth of a tuned circuit is 10 kHz at 1 MHz. Approximately what bandwidth would you expect it to have at 4 MHz?
ANS:
20 kHz
2. Using high-side injection for a 1-MHz IF, what is the frequency of the local oscillator when the receiver is tuned to 5 MHz?
ANS:
6 MHz
3. An IF filter has a –60 dB bandwidth of 25 kHz and a –6 dB bandwidth of 20 kHz. What is the shape factor value?
ANS:
1.25
4. Suppose a receiver uses a 5-MHz IF frequency. Assuming high-side injection, what would be the image frequency if the receiver was tuned to 50 MHz?
ANS:
60 MHz
5. Suppose a SSB receiver requires an injected frequency of 1.5 MHz. What would be the acceptable frequency range of the BFO if the maximum acceptable baseband shift is 100 hertz?
ANS:
1.5 MHz ± 100 hertz
6. The transformer of a double-tuned IF amplifier has a Q of 25 for both primary and secondary. What value of kc do you need to achieve optimal coupling?
ANS:
0.06
7. What value of transformer coupling would a double-tuned 10-MHz IF amplifier with optimal coupling need to get a bandwidth of 100 kHz?
ANS:
0.01
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