8/12/2019 1.pptxnn

1/29

Amplifier takes a relative small power inputcontrol signal controls and provides muchlarger power output into a load.

Input powerA. The control signal (low power)

B. The energy source (high power)

Gain

The gain of an amplifier is the ratio of themagnitude of the out put signal to that of the

magnitude of input signal

Amplifier parameter

8/12/2019 1.pptxnn

2/29

Amplifier parameter

Band width(pass band)

The separation between the two frequenciesat which the power gain has fallen to half mid-

band power gain (equivalent the voltage gainfalling to 0.707 of the mid-band voltage gain.)

Input impedance

This is the impedance offered by the amplifierto the input signal .Zin

8/12/2019 1.pptxnn

3/29

8/12/2019 1.pptxnn

4/29

Amplifier parameter

Radio frequency (RF) amplifier

Radio frequency amplifiers are used any where in thefrequency range 20 KHz to 30 GHz. Radio frequencyamplifiers are used to amplify radio frequency before

radiated to a transmitting aerial and also to amplifythe weak received signal

Direct coupled (DC) amplifiers

DC amplifiers, like video amplifiers are wide

band,specially for low frequency . Amplifier in cascade

When one amplifier is insufficient to give therequired two or more amplifiers are used in cascade.

8/12/2019 1.pptxnn

5/29

Amplifier parameter

The bel

Power gain in bels = Log10 Signal

power out

Signal power in

Power gain in decibels =

10 Log10 Signal power out Signal power in

8/12/2019 1.pptxnn

6/29

8/12/2019 1.pptxnn

7/29

Amplifier parameter

R-C coupling

Stage of amplification is required; the output

of one stage must be applied to the input of

the next stage.

Class A amplifier

A class a push-pull amplifier can thereforeproduce twice the power output of a single

ended stage with a lower level of distortion

8/12/2019 1.pptxnn

8/29

Amplifier parameter

Class B push-pull

In class B operation, the active device isbiased approximately at cut-off

Basic RF amplifier

Baseband frequencies are unsuitable forradio transmission .Modulation is carried out fortransmission.A radio frequency amplifier is designed toamplify only the carrier frequency or a narrow band of

frequencies on either a side if the carrier frequency

8/12/2019 1.pptxnn

9/29

Amplifier parameter

Class C bias

In order to maintain the oscillation, all that is

necessary is ensure that the losses in the

tuned circuit area restored, by regular input

from the power supply via The collector

current . short current pulses during positive

peaks

8/12/2019 1.pptxnn

10/29

Amplifier parameter

Transformer coupling

Transformer coupling is preferred for anumber if reason

Matching is easily achieved by adjusting turns ratio

Stray capacitances can easily be incorporated in thetuned circuit

band-pass response van be achieved by adjusting thetightness of circuits

8/12/2019 1.pptxnn

11/29

Amplifier parameter

Frequency multiplication

The tuned collector load can be arranged to havea resonance frequency of twice or three timesthe frequency of the input signal by harmonics

General principles

If the signal fed back is in anti phase to the input

signal, the feedback is negative. Positive feedbackincreases the gain and can cause oscillation

8/12/2019 1.pptxnn

12/29

ASP

Output impedance

The effects of applying negative feedback to anamplifier may be summerised as follows

The gain Is decreased

The gain stability is increased

The bandwidth is increased

Distortion and noise produced within the feedback

loop is decreased The input and output impedance are altered, the factor

(1+BA)

8/12/2019 1.pptxnn

13/29

ASP

Moving coil telephone

A telephone is a transducer which convertselectrical energy into sound energy

Loudspeaker performance

The minimum power to operate a moving coilloudspeaker is about 50 mV.

The impedance of moving coil is low, usuallyvalue being 3 ohm, 5 ohm, 8 ohm, 10ohm and 15ohm.

8/12/2019 1.pptxnn

14/29

ASP

Service selection

This provider the means for the flight crew to communicatewith the ground stations, each ASP operating quiteindependently of the others.

Flight interphone

This permits the flight deck crew to communicatewith each other.

Cabin interphone This is allows the flight and cabin crews to

communicate with each other.

8/12/2019 1.pptxnn

15/29

ASP

Service interphone

This provides the ground crew with the means to

talk directly with each other and to communicate

with flight or cabin crews at the same time.

A call system is usually included to attract the

necessary attention.

In some aircraft all the interphone systems mayoperate through a single amplifier unit, though

individual amplifiers are used.

8/12/2019 1.pptxnn

16/29

ASP

Passenger address or cabin address

This permits both cabin crew and flight deck crew tocommunicate to the passengers; usually a priority system ofcommunication is included.

Passenger entertainment

In a simple system this provides taped music to thepassengers. In large aircraft, e.g. Boeing 747, in-flight movies

as well as music are provided.

Emergency switch on ASP for To bypass isolation amplifier tothe headsets or loudspeakers and To bypass the normal PTTand mic relays to the selected panel

8/12/2019 1.pptxnn

17/29

ASP

Transmitter selection

These switchespermit the selection of a single transmitter, one perASP, normally annotated VHF1: VHF2: VHF3: HF1: HF2: PA

When used it connects the PTT and microphone lines to the

selected facility, usually via relays.

Receiver selection

These switches permit the selection of the radio receivers. Unlike

the transmitter selection, as many receivers as desired, may beselected to be listened to simultaneously.

8/12/2019 1.pptxnn

18/29

ASP

Isolation Amplifier

Sometimes referred to as the isolation amplifier, thisprovides a measure of gain to the received signals, inorder to overcome the attenuation effects of 'anti-

crosstalk' isolation. The amplifier may be fittedexternally in a separate unit.

Normal-emergency switch

This is included to provide service selection in theevent of either an isolation amplifier failure or othermalfunction in normal operation.

8/12/2019 1.pptxnn

19/29

ASP

Voice range filter

These are used to provide a notch filter at 1020Hz on both ADF and VOR operation reducing the

1020 Hz on voice and increasing it on range

Volume control

Permits the aircrew to adjust the volume to asuitable level in the earphones or cockpitloudspeaker.

8/12/2019 1.pptxnn

20/29

ASP

Differences between light and large aircraft PAsystem

Light aircraft systems usually have only twospeakers. Large aircraft systems usually haveapproximately 30-50 speakers.

Light aircraft have no priority switching,whereas large aircraft do.

Light aircraft use separate speakers forpassenger entertainment. Large aircraft use samespeakers for announcements and entertainment.

8/12/2019 1.pptxnn

21/29

ASP

Input and priority

Flight crew announcements

Cabin crew announcements

Prerecorded announcements

In-flight movie and music

Boarding music

In the event of an emergency any message input will assume thehighest input priority.

ASPs control

Single ASPs control passenger address in light aircraft

8/12/2019 1.pptxnn

22/29

ASP

Fail safe

"Fail safe" provision in transmitter serviceselection is arranged to ensure that if the relay,transistor or other component fails then thefailed path always connects the mic and PTT linesto the service

ASPs control

Single ASPs control passenger addressin light aircraft

8/12/2019 1.pptxnn

23/29

Communication System

Types of modulation

Amplitude modulation(AM)

Frequency modulation(FM)

Phase modulation

Pulse modulation

VHF Comms and HF Comms - AM

8/12/2019 1.pptxnn

24/29

Communication System

Power in modulated wave

v2

RL

M = peak value of envelop Peak value of unmodulated Carrier

Advantages of SSB over DSB

Power saving

Bandwidth reduction

8/12/2019 1.pptxnn

25/29

Speech modulation

Speech modulation shows varyingamplitudes of any frequency components of

speech superimposed on a 500 KHz carrier oron the final selected RF.

Increased power

The increased power in the side bandsdepends upon the modulation index m

8/12/2019 1.pptxnn

26/29

Communication System

Ionosphere effect

Low and medium frequencies, LF and MF, are

rapidly absorbed but will follow the earths

curvature if enough power is available

High frequencies, HF, may be bent or refracted

by the various ionosphere layers so that the

signals come back to earth, where they arereflected back to the ionosphere, to give multiple

hop communications using medium power

8/12/2019 1.pptxnn

27/29

Communication System

Very high frequencies, VHF and above, travel

in a straight line (line of sight) and are not

much affected by the ionosphere.

Power output

Pc + Pboth SBs PUSB only

8/12/2019 1.pptxnn

28/29

8/12/2019 1.pptxnn

29/29