How a radio transmitter circuit mixes audio with carrier wave?

[prabhatkarpe4]

I need to know how a radio transmitter circuit mixes audio signal with a radio wave (carrier wave)?

Is this mixing called modulation?

Why is an oscillator required in a radio circuit?

[Andy Chee]

Yes, you can call this mixing modulation.  Most commonly known are AM (amplitude modulation) and FM (frequency modulation).

An oscillator creates the radio frequency carrier wave, for example, AM radio frequency might be 500kHz to 1.6MHz and FM radio frequency might be 80MHz to 108MHz.

If you don't use a carrier, then you have to transmit the audio signal baseband 20Hz to 20kHz, which are *extremely* long wavelengths in radio waves.

[TimFox]

Technically, AM might be considered mixing, but FM is a different process.
If interested, you should consult the literature on FM, since the different methods of doing the modulation are quite interesting.
Also, the spectrum generated by FM is complicated, involving Bessel functions, while the AM spectrum is simple.

[A.Z.]

I need to know how a radio transmitter circuit mixes audio signal with a radio wave (carrier wave)?

Is this mixing called modulation?

Why is an oscillator required in a radio circuit?

why don't you get some decent textbooks (there are a lot for free), STUDY them, and then make yourself some educated guess ?

[CaptDon]

Stop and think for ten seconds, where would the carrier come from without an oscillator?? I'll give you a clue, where would the sound (audio carrier) of a whistle come from without a whistle? One simple explaination of AM modulation is raising and lowering the supply voltage to an oscillator (bad idea as it will also cause some FM shifting) or raising and lowering the supply voltage to the R.F. buffer or final amplifier thereby changing the amplitude of the carrier and generating sidebands.

[Randy222]

Modulation comes in many ways. The carrier is modulated in some way, and then the receiver must be able to process that modulation.

FM
AM
DMR
WiFi7 has a neat modulation scheme
and many others

[TimFox]

Back to simple modulation, for "AM".
One way to get amplitude modulation is to use an analog multiplier, where V_out = X x Y / H, where X and Y are the two input voltages and H is a constant factor.
All three terms and the output are measured in Volts.
The RF (carrier) signal is Y(t) = C x cos(wt), where C is the constant amplitude of the RF carrier.
It comes from the oscillator.
Let the audio signal be A(t), where the waveform A has 0 DC value (since it only goes down to, say, 20 Hz), and the peak-to-peak value is 2 V (so the waveform varies between -1 V and +1 V).

For "regular AM" (which contains the carrier and both sidebands), let Y(t) = C x cos(wt)  and  X(t) = (1 V) + A(t) , which ranges from 0 to +2 V.
When the audio signal A(t) goes through 0, the output is the carrier  C x cos(wt) / H , remembering the scale factor.

For "double-sideband suppressed carrier" (DSB), we drop the extra 1 V and simply let X(t) = A(t), giving the output XY/H = C x cos(wt) x A(t) /H .
When the audio signal A(t) goes through 0, the output is 0. 
 
When the music stops, there is no output for DSB, while the AM output is the carrier power.
The carrier carries no information, and can be considered wasted power.
However, it allows the modulated signal to be de-modulated using a simple diode rectifier and low-pass filter, as found in normal AM radios.

[iMo]

https://www.eevblog.com/forum/beginners/newbies-please-read-before-posting-24542/

[A.Z.]

https://www.eevblog.com/forum/beginners/newbies-please-read-before-posting-24542/

totally correct and agreed, but please, please; check the posts (and threads) history of the OP