Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

HELP with am/fm simultaneous transmitter

Status
Not open for further replies.

engineeer

New Member
AM FM Simultaneous Transmitter Using Digital IC

I need some help and information about this am/fm simultaneous transmitter using digital IC.
I found it at internet but I can't find some further information about how it works. I mean about the exact procedure and work.

It is of high importance because I need it for my university project.
So I would be grateful If someone could help me find out the details.

Thank you in advance!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Projects on that site rarely work, and are useless when they do - on just a brief glance that horrible circuit has at least two vital components missing, and wouldn't work anyway.

It's such a poor circuit that you wouldn't get decent marks for it at University - I wouldn't give any marks for it at all. Assuming it's redesigned to work as it's supposed to, it's probably a suitable school project for 11-12 year olds?.
 

mneary

New Member
I can't find some further information about how it works.
Simple: It doesn't work.

It was probably placed there to trick students who know nothing about electronics.
 

engineeer

New Member
well actually it is in a project that a professor at university gave to us...so please..since you know that it doesn t work tell me why and give me some tips about it...
he said that it works...help me confirm to him that it doesn't.
 

mneary

New Member
Q1 collector voltage extremely low with no headroom for audio.

Q2 has no base current so it is cutoff.

Xtal is unloaded. Frequency unpredictable.

CD4001 is operated far outside its operating speed.

Pins 1, 2 have no input bias. One might work, but most won't.

Circuit would produce 20, 40, 60, 80, 120....etc.MHz if it worked. These frequencies are illegal to use without license.
 

engineeer

New Member
The tasks are

1)Identify the circuit ( transmitter/ amp/ filter)

2)Analyze of the circuit

3) Frequency responce or another description of the behavior of the circuit

4) If it worked how would you order the parts?

Now since the circuit is problematic what do you think I should write to the professor? And how could I answer these questions???

Many many thanks !!!!!!!!!!!!!!!!!!!!!
 

mneary

New Member
Are not the questions well within the realm of what's expected of you having attended the lectures?
 

engineeer

New Member
no it's not something from the lectures otherwise i 'd probably know it. it 's a project for some extra credits i need before having the exams. Mostly i'm concerned in networks and that kind of lectures. Electronics is a lesson i chose for general knowledge. So i'm not specialised like you guys. That's why i need your help
 

audioguru

Well-Known Member
Most Helpful Member
Maybe you are supposed to fix the circuit:
1) Bias the first transistor and second transistor properly.
2) Make a real crystal oscillator with an IC that works as high as 20MHz like a 74HC04.
3) Make an AM modulator and an FM modulator.
 

engineeer

New Member
ok...actually the task isn t to fix the circuit but to explain the things i asked you before..
so i will try to answer them..

i think that it consists of an amp and a transmitter..
i can t find the frequency response!!!
and i can 't bias the tranzistors properly...although I understood the problems..
 

audioguru

Well-Known Member
Most Helpful Member
The preamp transistor is a thermometer, not an audio preamp.
The second transistor has no bias voltage so it does almost nothing.
The CD4001 has a max frequency of about 5MHz so it does nothing at 10MHz or 20MHz.
The CD4001 circuit is not an oscillator. If you make it an oscillator then its max frequency is about 5MHz with a 10V supply.
 

engineeer

New Member
Thank you for your help.
But I still can t finish the project about that circuit ...because I can t fix it...

I know that for transmision we need a modulator.. CD4001 does that work? or not? Because it only constists of nor gates....
and what is exactly the problem with the amps?
 

audioguru

Well-Known Member
Most Helpful Member
I know that for transmision we need a modulator.. CD4001 does that work? or not? Because it only constists of nor gates...
The modulation input is the input of a gate at pin 6 but the output of that gate at pin 4 is not connected to anything. Its other input at pin 5 is also not connected to anything.
The gate with inputs at pins 1 and 2 and an output at pin 3 is not an oscillator.
The other two gates are not turned off properly.

what is exactly the problem with the amps?
The first transistor is not biased correctly so it is saturated if its gain is high or when it is warm, and it is cutoff when its gain is low or when it is cold.
The second transistor is not biased so it will randomly conduct sometimes.
 

engineeer

New Member
The modulation input is the input of a gate at pin 6 but the output of that gate at pin 4 is not connected to anything. Its other input at pin 5 is also not connected to anything.
The gate with inputs at pins 1 and 2 and an output at pin 3 is not an oscillator.
The other two gates are not turned off properly.


The first transistor is not biased correctly so it is saturated if its gain is high or when it is warm, and it is cutoff when its gain is low or when it is cold.
The second transistor is not biased so it will randomly conduct sometimes.

how can I make a real oscillator?
how can I bias the two amps correctly?

I really appreciate your help
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
how can I make a real oscillator?
Look at Cmos Crystal Oscillator in Google. There are thousands of circuits. The designer of the circuit found by your teacher doesn't know anything about electronics. Maybe your teacher doesn't know anything about electronics.

how can I bias the two amps correctly?
Learn about transistors.
 

Attachments

  • Cmos crystal oscillator.PNG
    Cmos crystal oscillator.PNG
    12.2 KB · Views: 499
Last edited:

audioguru

Well-Known Member
Most Helpful Member
Your NXP/Philips document does not show its crystal oscillator circuit.
 
Status
Not open for further replies.

Latest threads

Top