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How to design a half duplex radio?

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cure9185

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I am an electronics and communication engineering student and we need to pass a project that uses amplitude and frequency modulation process. Is it possible that I can apply it to a design of a half duplex radio such as the walkie talkie? I need help because we have to make our own design. I have no idea on what components to include in my design. Thank you very much!
 

throwaway18

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>A project that uses amplitude and frequency modulation process.

How about making somthing that puts several audio channels down
a single cable using different carriers?

>Is it possible that I can apply it to a design of a half duplex
>radio such as the walkie talkie?

It depends on the radio laws in your country and your ability
to design a walkie talkie. You will need a frequency counter.

You will need to find a frequency you can legally use.

>I need help because we have to make our own design.

Google. Books. You can find all the information you need yourself
without bothering us with general questions.
If this is a long term project perhaps you have time to
get an amateur radio license?

Designing a good walkie talkie brings together a lot of areas of
electronics.

You need to make sure the transmitter output only contains
energy in the channel you are transmitting on. Nonlinearitys in
the amplifier can produce energy on other frequencys that
could cause interference to other radio users.

You need a low noise rf amplifer for the receiver input.

For AM you need AGC (automatic gain control) in the amplifer
stages so that strong signals are not clipped and weak
signals are not too quiet.

You need a reasonable impedance match between the antenna
and the receiver input and transmitter output.
The different sections in the radio (rf amplifiers, filters)
need to be impedance matched.

You need the receiver to not fail when it's connect to
the same antenna as the transmitter.

You need a stable and low noise oscillator to set the
carrier and receiver frequencys.

For a demo project you can make somthing fairly simple that
is not very good as walkie talkies go but will work
over a few tens of meters.

You could make a simple FM walkie talkie for 433.0MHz.
For the transmitter get a crystal cut for a lower frequency
that you can multiply up such as 433/24=18.04167MHz

Three single transistor multiplers at x3,x3,x4 then a buffer
stage to give you a few milliwatts of RF.

1mW will work for hundreds of meters outside with no obstructions
in the way. If you keep the power very low you won't bother
other radio users even if energy outside the channel is ot as well supressed as it should be.

Feed audio from a microphone into a varactor diode in the
crystal oscillator circuit to frequency modulate the transmitter.

A relay to switch the antenna between the transmitter and
the receiver circuits.

A single chip FM receiver if you can find one that will
work at 433MHz.
 

    cure9185

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cure9185

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>For a demo project you can make somthing fairly simple that
is not very good as walkie talkies go but will work
over a few tens of meters.

You gave me an idea. How about if I will only design for demo purpose only? I don't need a licence right? Can you show me a design of it? I will use it as my guide because we have not yet discussed about it. Thanks a lot!


cure9185
 

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