Questions and answers of "Fundamentals of RF circuits" in the first semester of the 22nd academic year of Xi'an University of Electronic Science and technology

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The first 1 page （ common 3 page ）

Learning Center / Correspondence Station _

surname name

learn Number

School of network and continuing education, Xi'an University of Electronic Science and Technology

2022 The first semester of the academic year

《 RF Circuit Foundation 》 Final exam questions

（ Comprehensive homework ）

Question no

One

Two

3、 ... and

Four

Total score

The topic points

25

20

15

40

score

Test instructions ：

1、 Release time of big homework test questions ：2022 year 4 month 22 Japan ;

2、 The exam must be completed independently , If you find plagiarism 、 The same score is zero ;

3、 The answer must be 《 School of network and continuing education, Xi'an University of Electronic Science and Technology 2022 Spring final exam answer sheet 》（ individual

Personal answer sheet ） Handwritten completion , The handwriting is required to be neat 、 The roll surface is clean 、 neat ;

4、 Photos should be complete 、 Clear , A picture corresponds to a personal answer sheet （A4 paper ）, Upload correctly .

One 、 Completion （ Every empty 2.5 branch , common 25 branch ）

1． High frequency small signal resonant amplifier works in

class , The resonant power amplifier works in

class .

2． The high frequency amplifier uses the tuning loop as the load , Its main function is to

、

.

3． The three terminal oscillator is built on

Based on feedback , Its composition principle is

.

4． Intermediate frequency fI＝10.7MHz The superheterodyne receiver , When receiving signal frequency fc＝104.3MHz, Local frequency

by

, The image interference frequency is

.

5． The crystal function of the series quartz crystal oscillator is , Parallel quartz crystal oscillator crystal action

by

.

Two 、 Multiple choice questions （ Every little question 2 branch , common 20 branch ）

1． The modulation that carries the message change on the carrier frequency change is called

A．AM

B．FM

C．PM

D．DM

2． To improve efficiency , Resonant power amplifier collector current angle θ

90o

A． Greater than

B． be equal to

C． Less than

D． Undetermined

3． Want to work with high power and efficiency , Resonant power amplifier should be selected to work in

state

A． Overvoltage

B． critical

C． Undervoltage

D． end

4． The maximum amplitude of a single frequency modulated ordinary amplitude modulated wave is 0.8V, The minimum amplitude is 0.2V, Then the amplitude modulation coefficient ma by

A．100%

B．80%

C．60%

D．20% The first 2 page （ common 3 page ）

5． Diode balance circuit cannot be realized

function

A． Amplitude modulation

B． Amplitude demodulation

C． mixing

D． Frequency modulation

6． The core of spectrum linear shift circuit is

A． Multiplier

B． adder

C． Subtracter

D． Phase detector

7． The information of phase modulation wave is sent in ________ Changing

A． phase

B． frequency

C． The amplitude

D． power

8． The signal whose envelope is proportional to the absolute value of the modulated signal is

A．AM

B．DSB

C．SSB

D．VSB

9．FM radio , Carrier frequency 108MHz, Audio 15kHz, FM index equals 5, The bandwidth of the radio station is about ______________

A．10kHz

B．30kHz

C．180kHz

D．216MHz

10． Synchronization in synchronous detection refers to

A． Same frequency 、 The amplitude is the same

B． In the same way 、 The amplitude is the same

C． Same frequency 、 In the same way

D． Same frequency 、 In the same way 、 The amplitude is the same

3、 ... and 、 Multiple choice questions （ Every little question 2.5 branch , common 15 branch ）

1． The characteristics of high frequency resonant power amplifier are

A. Big signal

B. nonlinear

C. Low distortion

D. Negative bias

2． The resonant power amplifier was under overvoltage , Through adjustment It can work in a critical state A． Reduce the load

B． Reduce the excitation amplitude

C． Reduce UBB D． increase UCC

3． The correct correspondence between radio band and modulation mode is

A. Zhongbo -AM

B. Ultrashort wave -AM C. Zhongbo -FM

D. Ultrashort wave -FM

4． Sine wave oscillators can be divided into

.

A．LC oscillator B． Crystal oscillator C．RC oscillator D． Relaxation oscillator

5． Use high frequency power amplifier to realize amplitude modulation , The correct choice of power amplifier state is

.

A． Base amplitude modulation selects overvoltage state

B． Under voltage state of base amplitude modulation and selection

C． Collector amplitude modulation selects overvoltage state

D． Collector amplitude modulation selects undervoltage state

6． The signals that can be demodulated by synchronous detector are

.

A．AM

B．DSB

C．SSB

D．FM

Four 、 Comprehensive questions （ Each question 10 branch , common 40 branch ）

1． Transmitter load RL=100Ω Output on u0(t)=4(1+0.5cos2π104 t)cos2π105t V

（1） Try to draw the waveform and spectrum of this signal ;

（

2） Calculate the total output power Pav、 Carrier power Pc And side frequency power P Side frequency ;

（

3） Draw the block diagram of realizing this signal with multiplier and adder .

2． Pictured 1 Diode bridge circuit shown ,u1=U1cosω1t,u2=U2cosω2t, And U2>>U1, All four diodes are

Ideal diode and linear time-varying state

（1） seek uo expression ？

（

2） Explain what functions the circuit can accomplish （ Just point out two ）,u1、u2 What signal should be added ？ What kind should be used

Type output filter ？

chart 1 The first 3 page （ common 3 page ）

3． The dynamic characteristic curve of the known high-frequency resonant power amplifier is shown in the figure 2 Shown ABC Broken line , Try to analyze and calculate

（1） Collector supply voltage UCC;

（

2） Collector current angle θ;

（

3） Base DC bias UBB;

（

4） What state does the amplifier work at this time ？

4． chart 3 The circuit shown is the AC equivalent circuit of the oscillator ,

f1 by L1C1 Resonance frequency of series circuit ,

f3 by L3C3 Series connection

Resonant frequency of the loop , ask ：

（1） Under what conditions can the circuit oscillate ？ The oscillator type is ？

（

2） oscillation frequency f0 And f1、

f3 What does the size of matter ？

（

3） Try to design the bias circuit , Form a complete oscillator .

L1

L3

C1

C2

C3

f1

f3

chart 3

chart 2