FREQUENCY MODULATION BEE

Who was the inventor that put the grid in the vacuum tube making the first voice and music amplifier?

Who was the inventor that put the grid in the vacuum tube making the first voice and music amplifier?

Lee Deforest

Who invented Frequency Modulation?

Who invented Frequency Modulation?

Maj. Edwin Howard Armstrong

Name the president of RCA who manufactured the Superheterodyne receivers and developed television.

Name the president of RCA who manufactured the Superheterodyne receivers and developed television.

David Sarnoff

Name two advantages of FM over AM

Name two advantages of FM over AM

1. Greater noise immunity; less noise and static.

2. Less interference due to capture effect.

3. Greater efficiency; more carrier power shifted to the sidebands

What is the greatest disadvantage to FM compared to AM?

What is the greatest disadvantage to FM compared to AM?

Requires greater bandwidth.

Why does FM require more bandwidth than AM?

Why does FM require more bandwidth than AM?

More sidebands.

info

carrier

FMmodulator

TimeDomain

sidebandsfc SIDEBANDS:

toswholeallnnff mc '#

mf

cf

1KHz

100KHzKHz

LSBS USBS

cf

96 97 98 99 100 101 102 103 104

How much bandwidth does each AM broadcast station get?

How much bandwidth does each AM broadcast station get?

10 kHz

How much bandwidth does each FM broadcast station get?

How much bandwidth does each FM broadcast station get?

200 kHz

How much more bandwidth does wideband FM require over standard AM?

How much more bandwidth does wideband FM require over standard AM?

5 Times.

Name two applications of FM besides Broadcast FM radio.

Name two applications of FM besides Broadcast FM radio.

1. Broadcast TV sound

2. Two-Way Mobile Radio

3. Cellular, paging, cordless phones

4. Data Communication

5. VCR

6. Wireless microphones

What is the term in FM that means the amount of frequency change to one side of the carrier?

What is the term in FM that means the amount of frequency change to one side of the carrier?

Deviation

The number of sidebands generated by Frequency Modulation are:

The number of sidebands generated by Frequency Modulation are:

1. 2

2. 4

3. Infinite

The number of sidebands generated by Frequency Modulation are:

3. Infinite

If the carrier deviates 75 kHz, what is the carrier swing?

If the carrier deviates 75 kHz, what is the carrier swing?

150 kHz

If the carrier deviates 75 kHz and transmits a 15 kHz tone, what is the modulation index (m)?

If the carrier deviates 75 kHz and transmits a 15 kHz tone, what is the modulation index (m)?

5kHz15

kHz75m

frequencyoinf

deviationm

What reference can you use if you know the modulation index and want to know how many sidebands are significant?

What reference can you use if you know the modulation index and want to know how many sidebands are significant?

Bessel Function Chart

An FM signal has a modulation index of 5 and a carrier of 10Vrms. What is the amplitude of the second sideband?

An FM signal has a modulation index of 5 and a carrier of 10V rms. What is the amplitude of the second sideband?

0.5 V rms

The importance of Bessel Functions is given modulation index (m), you can determine the bandwidth requirements.

True or False?

The importance of Bessel Functions is given modulation index (m), you can determine the bandwidth requirements.

True

Name the type of FM modulation where the information voltage directly controls the frequency of the modulated carrier.

Name the type of FM modulation where the information voltage directly controls the frequency of the modulated carrier.

Direct FM modulation

Name the type of FM modulation which is crystal based and uses frequency multiplication.

An indirect modulator uses the following: 1. 250 kHz crystal deviated 20 Hz 2. Multiplied times 81 3. Mixed with 20 MHz 4. Multiplied times 81

What is the final carrier frequency and final carrier deviation?

250 KHzCarrier

20 HzDeviation

Carrier

Deviation

X 81Carrier

Deviation

X 81Carrier

Deviation20MHz

Sum filtered off

DIFFERENCEFREQUENCY

Final Carrier Frequency =

Final Carrier Deviation =

250 KHzCarrier

20 HzDeviation

20.25 MHzCarrier

1.62 KHzDeviation

X 81250 KHzCarrier

1.62 KHzDeviation

X 8120.25 MHz

Carrier

131.22 KHzDeviation

20MHz

40.25 MHzSum filtered off

DIFFERENCEFREQUENCY

Final Carrier Frequency = 20.25 MHz

Final Carrier Deviation = 131.22 KHz

What does NBFM stand for?

What does NBFM stand for?

Narrow Band FM

Which uses more bandwidth, Wideband or Narrowband FM?

Which uses more bandwidth, Wideband or Narrowband FM?

Wideband FM

What is the highest information frequency transmitted on narrowband FM?

What is the highest information frequency transmitted on narrowband FM?

3 KHz

How much bandwidth is each user allocated on narrowband FM?

How much bandwidth is each user allocated on narrowband FM?

10 to 30 KHz depending on the application.

Name three agencies that use narrowband FM.

Name three agencies that use narrowband FM.

Police, fire taxis, hospitals, government and businesses.

Name the three components of the FM Stereo transmitted signal.

Name the three components of the FM Stereo transmitted signal.

1. L + R

2. L – R

3. 19 KHz pilot tone

A monophonic receiver uses which signal?

1. L + R

2. L – R

3. 19 KHz pilot tone

A monophonic receiver uses which signal?

1. L + R

Which signal turns on the red stereo light on the receiver?

1. L + R

2. L – R

3. 19 KHz pilot tone

Which signal turns on the red stereo light on the receiver?

3. 19 KHz pilot tone

Draw a frequency spectrum of the FM Stereo components that are multiplexed together and their frequencies.

Draw a frequency spectrum of the FM Stereo components that are multiplexed together and their frequencies.

FM broadcast radio receivers use the superheterodyne principle.

True or False?

FM broadcast radio receivers use the superheterodyne principle.

True

What is the IF frequency of FM broadcast receivers?

What is the IF frequency of FM broadcast receivers?

10.7 MHz

Name the stage of the FM broadcast receiver and state it’s function.

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

RF Stage- amplifies weak antenna signal and filters desired station

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

LO

Local Oscillator- produces a sinewave 10.7 MHz above the incoming RF

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

MIXER

LO

Mixer- combines local oscillator and RF producing sum and difference

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

MIXERIF

STAGE

LO

IF Stage- filter blocks sum and passes difference; and amplifies to level needed by the demodulator

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

MIXERIF

STAGELIMITER

LO

Limiter- clips off amplitude variations before demod

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

MIXERIF

STAGELIMITER

LO

FMDetector

FM Detector- removes info from the carrier

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

MIXERIF

STAGELIMITER

LO

FMDETECTOR

AFC

AFC (Automatic Frequency Control) – keeps the local oscillator from drifting

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

MIXERIF

STAGELIMITER

DEEMPHASIS

LO

FMDETECTOR

AFC

De-emphasis- low pass filter in receiver counteracts effects of pre-emphasis

Name the stage of the FM broadcast receiver and state it’s function.

RFSTAGE

MIXERIF

STAGELIMITER

DEEMPHASIS

AFAMP

LO

FMDETECTOR

AFC

AF AMP- power amplifier to drive the speaker

What is pre-emphasis?

What is pre-emphasis?

High pass filter in transmitter boosts high frequencies to overcome noise

What is the circuit that quiets an open receiver channel when no signal is present?

What is the circuit that quiets an open receiver channel when no signal is present?

Squelch

Name the FM demodulation circuit where a VCO follows the phase comparator

Name a piece of test equipment which is essential to the signal analysis of an FM transmitter.

Name a piece of test equipment which is essential to the signal analysis of an FM transmitter.

Spectrum Analyzer