AM demodulator

Hi!

Please let me know why need this last stage (Non-Inverting opamp with gain 2) ?

Is is possible to connect without this last stage but only one capacitor to eliminate DC ?

Regards,

It's an "impeadance transformer." You need it to drive the speaker's impeadance.

You won't get much volume from an 8 ohm speaker using a 741 op amp. You need an audio amplifier for that.

The entire circuit is absolute rubbish, it most have been 'designed' by a complete idiot, and won't work.

1) The horrible circuit has its first opamp as an inverter that has a low input impedance of 5.1k ohms. Therefore it causes the selectivity to be low because the tuned circuit is a heavily loaded. If the opamp has a non-inverting input then its input impedance would be very high and the selectivity would be much better.

2) The circuit has only a single tuned circuit so its selectivity will be pretty bad when compared to a normal radio that has many tuned circuits.

3) The very old opamp used as the RF amplifier has a poor high frequency response. Its max gain at 1.6MHz (the top of the AM broadcast band) is only 3.
Its max output level at 1.6MHz is only 2V p-p.

4) The detector diode should be inside the negative feedback loop of a good RF opamp for good sensitivity.

5) The circuit is missing automatic-gain-control like all normal AM radios have so that weak and strong stations have the same volume level.

6) The circuit is missing a power amplifier to drive a speaker.

I wonder why the circuit needs two 18V batteries??

Don't tell me your college lecturer tasked you with building this crappy circuit? If so he needs to be sacked.

I found this circuit on internet (one random page). I need (for college) to design and explain one simple AM demodulator + amplifier. (how does it works...).

Can you give me one simple circuit like that (which works )

Thanks,

sniper007 said:

I found this circuit on internet (one random page). I need (for college) to design and explain one simple AM demodulator + amplifier. (how does it works...).

Can you give me one simple circuit like that (which works )

Thanks,

Click to expand...

Finding a poor circuit on the internet, and then asking for a working circuit does not equate to designing a circuit.

JimB

sniper007 said:

I found this circuit on internet (one random page). I need (for college) to design and explain one simple AM demodulator + amplifier. (how does it works...).

Click to expand...

If you produced that circuit as an assignment for me, you would be so kicked off the course

sniper007 said:

I found this circuit on internet (one random page). I need (for college) to design and explain one simple AM demodulator + amplifier. (how does it works...).

Can you give me one simple circuit like that (which works )

Thanks,

Click to expand...

So, can you explain how you think this circuit is supposed to work? eg. what is the diode and cap for?

I need to desing whole telecomunication system like:

thermistor -> wheatstone bridge -> instrumentation amplifier -> AM modulator

and

Am demodulator -> amplifier


I don't know if desing is right words, however i need to understand how this process works. (why bridge, why modulator, etc).

sniper007 said:

I need to desing whole telecomunication system like:

thermistor -> wheatstone bridge -> instrumentation amplifier -> AM modulator

and

Am demodulator -> amplifier


I don't know if desing is right words, however i need to understand how this process works. (why bridge, why modulator, etc).

Click to expand...

Your original posted circuit would be useless for what you propose.

As in your above flow diagram, design each block accordingly. Find a thermistor, figure out how to put it in a wheat stone etc...

I suspect you are expected to make this design yourself rather than take a bogus circuit off the internet.

If your unable to complete this assignment without outside help, then perhaps you might be better off re taking the class.

"If your unable to complete this assignment without outside help, then perhaps you might be better off re taking the class. "

Maybe rethinking your field of study!

microtexan said:

"If your unable to complete this assignment without outside help, then perhaps you might be better off re taking the class. "

Maybe rethinking your field of study!

Click to expand...

**broken link removed**