Low level AM Transmitter Circuit and little description.

[Eshal]

Hello experts!

How is everyone.

I am newbie here.

I am in the 4th semester of Electronics Engineering. Yet I have studied Basic electronics, LIC, and only analog electronics not yet digital. Also I don't have any knowledge about Power electronics because still we have not studied it yet as well.

So my Analog Communication teacher give us an assignment and told us to make the Low Level AM Transmitter.

Teacher said that we students can pickup any circuit diagram from internet and make a transmitter on the breadboard. And then we can submit only in 3 weeks. Our teacher knows that we student don't have much knowledge that we could design with our own knowledge so he recommend to pickup the diagram from internet.

But my thinking is not as my teacher. I want to learn something. If I pick it up from internet then I can't be able to learn anything. Therefore, I turned to this forum.

Please tell me about low level AM transmitter:
And please anyone of you provide me a low level AM transmitter circuit diagram with a little description of stages.

Please remember, it must with the consideration of analog electronics, not so hifi transmitter. It just transmit to a certain range. Please help me.

If you need any information you expert can ask.

Thank you.

 

[goldsmith]

Hi Eshal

So my Analog Communication teacher give us an assignment and told us to make the Low Level AM Transmitter.

Well , i think your teacher didn't tell you any thing regarding the specifications for instance how much power is required or how much is impedance of load ( what kind of antenna ) , and ... etc .
Well , about AM transmitters , at low powers , most important thing , is create a pure and fixed , sine wave . it can be derived from a crystal oscillator or some other oscillators or perhaps , oscillators that you can find in each electronic market !
second step is multiplying , amplified message signal with your pure sine wave . you will have many ways for this step . such as , using a message signal that summed with a DC signal , as your supply ( for latest stage ) . or perhaps using a simple diode multiplier ( or BE as a multiplication )
if you need higher powers ( i know you don't need it now ! ) you should only use first way that i have mentioned .
So , you should mention how much power or how much distance or what carrier frequency is your aim ! then we can start .
Best Wishes
Goldsmith

 

[Eshal]

Hello goldsmith!

Thank you for reply.

It is detailed reply to me. thank you very much.

No, my teacher didn't tell me anything of those things.

He just said that we student can get any circuit diagram from internet and show me by making circuit on breadboard.

But I think if you give me any circuit diagram of low level AM transmitter with approximately 30m range.

Thank you.

- - - Updated - - -

I just have 3 weeks for submission.

 

[goldsmith]

And what about frequency of station ? (carrier signal ) , if it is not important and if you want build it on bread board , you'd better to do it with 530 KHZ or perhaps 600 KHZ . thus it will be pretty easy for you ! , so see below , please :

some years ago i have designed this circuit , for frequency of 1MHZ . you won't need it's detector section . so you should just build it's oscillator section and then enjoy it !
( i think it can handle your aim because it is a simple regenerative transmitter )

Good luck
Goldsmith

 

[Eshal]

Oh thanks for this help.

And what about frequency of station ? (carrier signal )
My teacher didn't tell me about this. But I am amaze how my teacher test my transmitter? I think he would tell me to buy ready-made AM receiver.

Also goldsmith, what about range of this AM transmitter?

- - - Updated - - -

And I don't see any antenna in the circuit diagram. Because to transmit signals, it must have antenna. Isn't it?

 

[goldsmith]

Some comments ! at first you will need an oscillator as it's input . ( as you can see at the picture . ) you can easily make it .
But if you want simpler way , tell me about this : d you have access to the crystal oscillators with 4 pins ( 1MHZ ) in your country ? and what about HT50 ( red transformer ) ? if yes you can make it at 20 seconds !

And what about frequency of station ? (carrier signal )

What do you mean by that ?

My teacher didn't tell me about this. But I am amaze how my teacher test my transmitter? I think he would tell me to buy ready-made AM receiver.

Perhaps he has radiation meter , or perhaps he wants to test it with an oscilloscope . or perhaps he have a receiver !
And about antenna , , it will be derived from collector , via a capacitor . it can be a dipole antenna !

 

[Eshal]

at first you will need an oscillator as it's input . ( as you can see at the picture . ) you can easily make it .
But if you want simpler way , tell me about this : d you have access to the crystal oscillators with 4 pins ( 1MHZ ) in your country ? and what about HT50 ( red transformer ) ? if yes you can make it at 20 seconds !

Sir I don't know anything that what is allowed in my country and which is not.
I can't make any comment about it.

Can't you give me any ready-made circuit?

Perhaps he has radiation meter , or perhaps he wants to test it with an oscilloscope . or perhaps he have a receiver !

Yes, may be.

And about antenna , , it will be derived from collector , via a capacitor . it can be a dipole antenna !

You mean at the collector of Q2 above R12 in the circuit diagram?

Some more clearifications:
What is the range of this transmitter and is it low level or high level?

 

[Eshal]

Please goldsmith help me out of this problem. I wish, this project could complete in 3 weeks.

 

[LvW]

So my Analog Communication teacher give us an assignment and told us to make the Low Level AM Transmitter.
Teacher said that we students can pickup any circuit diagram from internet and make a transmitter on the breadboard.

Hi Eshal,

your question is a very general one - and, thus, it is not easy to give a substantial answer and a real help.
You didn't say anything about the carrier frequency and the modulation signal (single tone or a frequency band?).
In principle - as for each task within the area of circuit synthesis - there a many solutions.
Goldsmith already gave some hints for one possible circuit.
And I will try to give you some information on another approach:

According to my experience a very simple AM modulator consists of a basic differential amplifier. I suppose you have treated this circuit already in your courses.
The modulating signal is applied to the base of the current determining transistor in the common emitter path.
Thus, the gain of the device is controlled by this signal. The HF carrier is applied to one of the base nodes of the diff. amplifier. The other base pin can be grounded.
Then, the modulated carrier is available at one of the collector nodes.

As a second unit you need a HF source as a carrier. I think, one of the most simple oscillator circuits can be used: The WIEN type oscillator.
For a general-purpose opamp the frequency of this oscillator can be as high as 10 kHz.

In summary: A WIEN oscillator generates the carrier (up to 10 kHz) and this carrier is modulated by a NF signal using a differential pair.

One final question: What about an antenna? Required?

 

[Eshal]

@LvW Thanks for reply.

@LvW & @goldsmith

You didn't say anything about the carrier frequency and the modulation signal (single tone or a frequency band?).

I asked to the class-fellow. He said that sir says carrier frequency depends on the range. I don't know if it is true. Our teacher told us that this AM transmitter must be of atleast 100feet in range.

And our teacher said we can use any carrier oscillator other than crystal oscillator.

@goldsmithtell me about this : d you have access to the crystal oscillators with 4 pins ( 1MHZ ) in your country ?

I don't know if it is allowed in our country. But our teacher denied strictly to use crystal oscillator.

One final question: What about an antenna? Required?

Yes, ofcourse antenna is required.

 

[LvW]

So - what's your decision, Eshal? What kind of additional information do you need?
Carrier frequency?
Are you allowed to use integrated circuits (opamps, differential amps)?

 

[Eshal]

So - what's your decision, Eshal? What kind of additional information do you need?
Carrier frequency?

I need simple carrier oscillator.

Are you allowed to use integrated circuits (opamps, differential amps)?

I am just allowed 555 timer, 741C etc. In short, I am allowed to use those Integrated Circuits which are studied under course named "Linear Integrated Circuits"(LIC).
Does this make you understand, what I allowed or which isn't?

One more thing, as you(LvW) see in circuit given by goldsmith in post#4. Can you tell me what is the range of that circuit?
And as in this circuit, he used 2 frequency sources "V5" and "V6" having frequency of 15MHz and 15KHz, respectively. So I think I need 2 carrier oscillators one of 15MHz and other of 15KHz. Am I right?

 

[LvW]

I need simple carrier oscillator.

As I have mentioned - the WIEN oscillator is a simple one and easy to design. However, the technology and the circuit to be selected (opamp or transistor) depends strongly on the chosen carrier frequency.
In your case, I do not recommend a frequency in the MHz range. I think some hundreds of kHz are sufficient and easier to handle. However, I don't know if you are completely free to choose a frequency.

One more thing, as you(LvW) see in circuit given by goldsmith in post#4. Can you tell me what is the range of that circuit?
And as in this circuit, he used 2 frequency sources "V5" and "V6" having frequency of 15MHz and 15KHz, respectively. So I think I need 2 carrier oscillators one of 15MHz and other of 15KHz. Am I right?

Do you know what "modulation" means? There is one large carrier frequency that is modulated with a signal to be transmitted. This signal must have a frequency (a single ton or a spectrum like speech) much lower than the carrier. In the example mentioned by Goldsmith the carrier is at 1 MHz and the modulation signal at 15 kHz. That's all.

 

[Eshal]

In your case, I do not recommend a frequency in the MHz range. I think some hundreds of kHz are sufficient and easier to handle.

As you said hundreds of KHz are sufficient, so this mean would it provide 30m range?

However, I don't know if you are completely free to choose a frequency.

I told you above, our teacher didn't tell us anything about carrier frequency. He just told us about range. 100feet in range i.e. approx. 30m

In the example mentioned by Goldsmith the carrier is at 1 MHz and the modulation signal at 15 kHz. That's all.

So carrier is at 1MHz, this implies I need one carrier oscillator of 1MHz?

Thank you very much for all help.

 

[Eshal]

NO help !!!! :-(

:-(

 

[goldsmith]

Hi Eshal again and sorry for delaying to reply , after some days that i was not in my home when i came back , some unpredictable events happened then my time dissipated really and it made me very angry !
So lets back to the original guidance !

Sir I don't know anything that what is allowed in my country and which is not.
I can't make any comment about it.

Can't you go to the electronics market and ask regarding that ??

You mean at the collector of Q2 above R12 in the circuit diagram?

Of course !

So carrier is at 1MHz, this implies I need one carrier oscillator of 1MHz?

What do you think ? of course you will need that ! as i mentioned at past there are many ways for this purpose ! one o them is an oscillator with a transistor in series with supply ! but it's out put power will be low too !
One of the simplest ways for you is try to find that crystal oscillator that i have mentioned and then use a series RED transformer with it's supply path and then you will have an AM-FC wave ! simply and then you can amplify it and filter it easily !
By the way , i think LvW have replied all of your questions as well as possible , didn't you try to get the idea ?
Best Wishes
Goldsmith

 

[Eshal]

Can't you go to the electronics market and ask regarding that ??

My teacher is strictly forbidden to use crystal oscillator. So if I asked for it from market then it is of no use for me.

By the way , i think LvW have replied all of your questions as well as possible , didn't you try to get the idea ?

Actually, it is my first project. Shayaan told you that our department is not so good, they just come in the class teach us and go out of the class. It is first project. I don't know what LvW trying to said, I am understanding all his help but I am unable to get any idea as you are pointing out to get idea from LvW's discussion.

Again, our teacher forbid us to use crystal oscillator.

One more thing,
At 5 September 2012, we students have to submit proposal for low level AM transmitter i.e. components' costs and circuit diagram completely.
Don't you provide me a complete circuit diagram till tomorrow?

Thank you very much.

- - - Updated - - -

I am leaving by now. Because tomorrow, I mean today (Monday) I have to university. It is 2AM in my country. But please leave your reply.

Thank you.

Good morning goldsmith and LvW

 

[goldsmith]

My teacher is strictly forbidden to use crystal oscillator. So if I asked for it from market then it is of no use for me.

I don't know what is your teacher's reas reason , but no problem , you can use this circuit as your oscillator stage , easily , see below , please :

Actually, it is my first project. Shayaan told you that our department is not so good, they just come in the class teach us and go out of the class. It is first project. I don't know what LvW trying to said, I am understanding all his help but I am unable to get any idea as you are pointing out to get idea from LvW's discussion.

Read his statements again and more carefully and tell me which section isn't clear ! ( however i believe it is as clear as enough . )

Don't you provide me a complete circuit diagram till tomorrow?

If you need a complete circuit , i have thousands of these circuits in my designs . i can give you some of them easily , but you have told that you want learn , it is the reason that why i didn't give you the final circuit !

ctually, it is my first project. Shayaan told you that our department is not so good,

Yes shayaan have told me regarding this issue , and i told him that here is the same too ! ( an advice : try to learn yourself , instead of trying to rely on teachers of your university ! )
By the way where is shayaan now ? is he busy too ? because i didn't see him here any more ( this month ) .

I am leaving by now. Because tomorrow, I mean today (Monday) I have to university. It is 2AM in my country. But please leave your reply.

See good dreams ! and take care !
Goldsmith

 

[FvM]

Searching for "AM transmitter" at electronic boards and google will give you plenty of hits, possibly more than you can handle. Below two arbitrary links with some background information about antenna tuning and legal aspects.

http://www.zen22142.zen.co.uk/Circuits/rf/amtx.htm
http://www.bowdenshobbycircuits.info/page6.htm#amtrans.gif

Of course, if the project stays with pencil and paper, there's no legal issue. Before going to operate real stuff, I would expect some legal information from the teacher.

 

[LvW]

I am just allowed 555 timer, 741C etc. In short, I am allowed to use those Integrated Circuits which are studied under course named "Linear Integrated Circuits"(LIC).
Does this make you understand, what I allowed or which isn't?

Hi Eshal,

I have the feeling that you are under strong time pressure now. Of course, all of us want to help you - however, it is not easy for us because lack of information.
You are allowed "to use those Integrated Circuits which are studied under course named "Linear Integrated Circuits"(LIC)."

How could we know which IC's you have studied?
What means "741C etc".

For example, are you allowed to use a fast opamp with at least 10 MHz transit frequency? Remember: The 741 has only 1 MHz.
This is important because for carrier frequencies in the range of several hundreds of kHz the 741 cannot be used.
Of course, as an alternative you can use discrete transistors (instead of opamps) - but the design is more complicated.
Therefore, I have recommended an opamp based design (two units: Oscillator and differential amplifier IC). But you need a broadband opamp (as mentioned above).

And - as FvM has indicated - do not care about legal aspects at the moment. Make your choice (carrier frequency and design principle) and start to design and calculate parts values.
That's my recommendation.
Good luck.