# Help with AM modulator

1. Nov 15, 2008

### aruna1

urgent help with AM modulator

hello friends;
we have an exhibition in my university.my seniors asked me to make a AM modulator circuit to demonstrate AM modulation.They also provided me a circuit diagram of a AM modulator(level 4 lab sheet),But in that diagram some resistor values are not mentioned.I don't know how to calculate them because AM modulation is will be taught in next year and I have no idea about AM modulation.(I'm a level 2 student)

I'm attaching the diagram I have,Can some one take a look at it and help me to find missing values

PS
I have only today to make this circuit so quick help would be great

#### Attached Files:

• ###### lab5.pdf
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2. Nov 21, 2008

### JANm

Re: urgent help with AM modulator

You need a 1 megahertz oscilator. The most important part is the RC-time.
A quick stand in can also be a 4093 or a 40106 Smittrigger. An inverter makes a 0 to 1 and a one to zero. The smittrigger does this in a very special way. It has hysteresis.
I think a smitttrigger (v=5 volt) goes off at 2,32 volt and goes on at 2,3.
At the input of the smittrigger comes a triangle voltage betwee these to vaulues. at the output comes a full swing of nearly 5 volt.

A very nice way could be a 4051, which can bring a input to one of eight channels.
It is not the requested A type full multiplexer, but it can bring a B type Amplitude modulation...

3. Nov 21, 2008

### aruna1

Re: urgent help with AM modulator

ok didnt understand a bit

4. Nov 21, 2008

### JANm

Re: urgent help with AM modulator

Amplitude modulation is a way of communication. An oscilator of a certain frequency, in your case a 1 megahertz block switches form zero volt to 5 volt one million times a second.

A function with a frequency slower than this block (50 hertz<sound?<10.000 hertz) is to be communicated. If you sample the wave with the oscilator you get a function of changing amplitude. This signal can be transmitted. At the other side there is a receiver which can tune to 1 mehahertz. The receiver connects the samples with little lines (as you do when you draw graphs) physically this means filtering the 1 megahertz out of the signal and the receiver has the original sound.

For telefone things it is also usefull to have different calls through one line. The 4051 can make eight different call's through one line.