Electronics tutorial - Building an AM modulator

Really enjoying your RF stuff, thanks for posting

awesome video , today i learned how to build an am modulator

Your videos are awesome.. keep making projects. Also Start some intermediate course on such ckts and analytical methods that you use while developing a circuit, it will be huge help for people like us who wants to build intuition for designing ckts

I follow all the videos, congratulations, always high quality content!

Great video! You are such a good teacher.

This is quite a good effect to use in music recording studios.... you could spend hours with audio plugins to get a good "tuning in a radio" sound.... or.... you could just use a radio.

FesZ In order to understand an AM modulator it is necessary to understand WHY a circuit modulates the carrier. AM modulator requires MULTIPLICATION of the carrier AM= (Vm cos 2 pi fm )( Vc sin 2 pi fc ) where mod freq , fm' << fc , the carrier freq . A linear op-amp which sums Vm and Vc can NOT produce AM.

You don't need a non-linear element to create an AM modulator. You simply control the voltage on collector of the final RF PA stage so that the RF envelope changes in sympathy with the modulation. All you need is an audio amplifier and a transformer to couple to the RF PA stage.

Amazing!

Awesome. Any chance to get an fm version?

could you make the rf osc variable freq.

is the inductor connected to the output to the modulator and ground?

But can you make a radio amplifier for this transmitter circuit?

Make a video on costas loop demodulators

SIR Why RF INPUT IN COMMON EMMITTER AND AF INPUT IN COMMON BASE MODE ONLY. ?

Hello! I'm always watching your videos very beneficially ! But can you implement a PID controller in LTspice? I would like to receive the output from the boost converter as feedback and construct a circuit that controls the PWM, but I can't find any reference materials suitable at Google.

I sorry, but I didn't understand the part about the antenna, at the end - needless to say, I don't know much about antenna design; however, aren't all antenna's just emitting electric and magnetic waves. Isn't the coil you built to electro/magnetically couple the output signal to the radio just an antenna?

It's hard for me to write in English, so I don't have time to answer in time :) Let me explain. The AM modulator of your choice uses the nonlinearity of Ic vs Vb (as you know, this is an exponent, but we will consider it in a large signal mode, so for simplicity, we will replace the exponent with a straight line with a bend at 0.6V). In proper operation, both the low frequency signal and the high frequency signal must have an amplitude of 1Vpk-pk or more. It is good if they are equal in amplitude to each other. In this case, at the top of the positive half-wave of the audio signal, the high-frequency signal will pass to the output completely, at the top of the negative half-wave it will not pass at all, and when the audio signal passes through 0V, only the positive half-waves of the high-frequency signal will pass to the output. As you can see, the transistor operates in cutoff mode for a significant part of the time, and therefore the output signal will be very different from the modulated sinusoid. Therefore, instead of a resistor, a resonant circuit tuned to the carrier frequency is usually placed in the collector of the transistor. Without such a resonant circuit, the output signal spectrum will be very messy. Here are links to two figures that explain this: https://conture.by/wp-content/uploads/2011/12/mris23.jpg , https://conture.by/wp-content/uploads/2011/12/mris24.jpg Naturally, modulation will also occur at not optimal amplitudes of the input signals. It's just that the modulation depth will be much less. By the way, it is better to choose a smaller initial collector current (for example <1mA) in order to work in the place of the greatest nonlinearity. The Q factor of the resonant circuit should also be neither too large nor too small. I would recommend Q = 3 ... 6 - this is quite enough for signal smoothing. And of course, it should be admitted that although the input impedance changes (since hFE vs Ic changes), it does not affect the modulation process. Maybe you should have used some more intuitive modulator? For example, based on a field effect transistor or photoresistor in controlled resistance mode. It's up to you, of course.

“Building an amplitude modulator modulator” lol