how i design am transmitter

[Parth86]

how can i design am transmitter

hi

i am basic confused

in books, i read bunch of theory in pieces but i don't know how they work together. i have no idea where i would apply. so i fell difficulty

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i am trying to design am transmitter for short distance to learn basic calculations of transmitter

AM TRANSMITTER

modulations type am modulations
frequency range 1mhz
voltage supply 12v
transmitting distance 80m-100m
audio frequency 20hz-20khz
antenna
low level modulated with linear amplifier

i know i need following circuit to make transmitter
-audio amplifier circuit
-Oscillator circuit
-RF amplifier circuit
-microphone

i need circuit that amplify the signal of mics

i know to make amplifier circuit
transistor NPN, PNP transistor
mode ce, cb, ce
class A, B, C amplifier

for design audio amplifier we select following parameters
audio source -microphone
transistor npn transistor
mode common emitter
class class A power amplifier

transistor ratings
collector emitter voltage=30v
collector base voltage=60v
emitter base voltage=5v

collector current=800mA
power=500mW



my questions

1. specification of microphone
frequency response
impedance

2what is gain of audio amplifier

3.which stage is used for audio amplifier
single stage
two stage transistor

4.what is gain of rf amplifier

5.how we decide what gain is needed for signal

6.which oscillator is used and what is frequency

wien bridge
colpit
crystal

7.what is length of antenna

if possible please explain with mathematical calculations
i don't care bad quality of transmitter

 

[audioguru]

i am basic confused

Don't you have a teacher and a text book like all other students have?

AM TRANSMITTER

modulations type am modulations
frequency range 1mhz
voltage supply 12v
transmitting distance 80m-100m
audio frequency 20hz-20khz

Don't you know that a 1MHz AM radio receives only about 50Hz to 3kHz? Why do you want 20kHz?

i know i need following circuit to make transmitter
-audio amplifier circuit
-Oscillator circuit
-RF amplifier circuit
-microphone

Then show us the circuits you designed for the transmitter.

i need circuit that amplify the signal of mic

There are hundreds of mic preamp circuits shown in Google.

i know to make amplifier circuit
transistor NPN, PNP transistor
mode ce, cb, ce
class A, B, C amplifier

Select the type of circuit then show it.

for design audio amplifier we select following parameters
audio source -microphone
transistor npn transistor
mode common emitter
class class A power amplifier

Then show it.

transistor ratings
collector emitter voltage=30v
collector base voltage=60v
emitter base voltage=5v
collector current=800mA
power=500mW

Almost ANY transistor can be an audio amplifier but yours does not have a part number.
Show us your circuit.

my questions

1. specification of microphone
frequency response
impedance

Select which type of microphone:
Electret or Dynamic.

2what is gain of audio amplifier

The gain required depends on the transmitter's modulator circuit.

3.which number of stages is used for audio amplifier
single stage
two stage transistor

It depends on the amplifier circuit and the amount of gain needed.

4.what is gain of rf amplifier

It depends on how much output power you need (and the sensitivity of the AM radio) and the amount of output level from the oscillator.

5.how we decide what gain is needed for signal

Use common sense.

6.which oscillator is used and what is frequency

wien bridge
colpit
crystal

You listed the frequency above. Weren't you taught about AM transmitters and high frequency oscillators?

7.what is length of antenna

For your very short range the antenna can be very short or be a ferrite bar like used in AM radios.

if possible please explain with mathematical calculations

Why didn't you learn them in school?

 

[Parth86]

Don't you have a teacher and a text book like all other students have?

i have text books but in books lot of theory is given in pieces i feel difficulty how we apply for this circuit


Then show us the circuits you designed for the transmitter.
first i build block diagram of transmitter





Select which type of microphone:
Electret or Dynamic.

electret mic

The gain required depends on the transmitter's modulator circuit.
please give hint for this terms



Why didn't you learn them in school?[/QUOTE]

in school they teach me theory and how make amplifier oscillator circuit but they don't teach real example how we make transmitter with amplifier,oscillator circuit
i can make amplifier ,oscillator circuit when i know the input and output for circuit
but here my transmitter circuit i have no idea how we decide gain for this circuit please give idea how we decide gain for every transmitter

 

[audioguru]

First you must decide on the amount of output power the transmitter must give into a short antenna that does not match the very low frequency it operates at. You must know the sensitivity of the radio or measure it then calculate the output power needed for the range you want.

Then select an AM modulator which will have a certain input level required from the mic preamp. Then select an oscillator type.

I looked in Google for AM Radio Transmitter Circuit and there are many schematics.
The 3rd link has a fairly simple circuit.
The 4th link has Wikipedia showing how to design an AM Radio Transmitter.
There are hundreds of more good links about it.

 

[Parth86]

thanks audioguru this is vary helpful for me