Modulating with a square wave will give you a buzzing sound, not a tone.
Your 555 output should have a duty cycle of about 50%. Currently it looks like it is more than 90%.
The 555 output is too large and is almost completely killing the oscillator output. This actually becomes On-Off Keying of the carrier.
You need to pass the output through a capacitor to remove the DC component.

Your circuit is too simple to get good results but you will probably be able to hear it in the receiver.

Hi, thanks for your answer. I just changed the duty cycle to 50%, and added the coupling capacitors. Do you mean that the amplitude of the 555 output is too big? I know that modulating the carrier with a square wave isn't ideal, but there's no way to produce a 600 Hz sine wave with an LC tank, right?

 

Why not use a phase shift oscillator for the tone. How clean and stable do you want to go?

What are you keying with? A manual key?

 

Thank you so much! Is this what it's supposed to look like?

The 100Ω resistor between the oscillator and the supply should be moved to the other side of the transistor. A small thing which may make no difference, but it lowers the voltage at the emitter.

Yes, now the output looks more like what we'd expect.

 

Hi, thanks for your answer. I just changed the duty cycle to 50%, and added the coupling capacitors. Do you mean that the amplitude of the 555 output is too big? I know that modulating the carrier with a square wave isn't ideal, but there's no way to produce a 600 Hz sine wave with an LC tank, right?

Ordinarily you want to have the maximum modulation possible. Usually the modulation would be an audio signal and you would get amplitudes that vary over a wide range. With a square wave you get two amplitudes. If the modulation signal is too strong it will actually cut off the oscillator and you are not using amplitude modulation, it has become On-Off Keying. On-Off Keying is used in simple digital RF control applications.
A 600Hz sine wave oscillator can be created with an opamp: https://www.nutsvolts.com/magazine/article/op-amp-cookbook-part-3

 

Why not use a phase shift oscillator for the tone. How clean and stable do you want to go?

What are you keying with? A manual key?

The signal doesn't have to be very clean for my project, but I'll see if I can replace the 555 timer with the phase shift oscillator. Thanks for the idea. My key is probably just going to be something improvised with a metal strip that you can hold down, because I don't have a real one.

 

The 100Ω resistor between the oscillator and the supply should be moved to the other side of the transistor. A small thing which may make no difference, but it lowers the voltage at the emitter.

Yes, now the output looks more like what we'd expect.

Thanks!

 

Ordinarily you want to have the maximum modulation possible. Usually the modulation would be an audio signal and you would get amplitudes that vary over a wide range. With a square wave you get two amplitudes. If the modulation signal is too strong it will actually cut off the oscillator and you are not using amplitude modulation, it has become On-Off Keying. On-Off Keying is used in simple digital RF control applications.
A 600Hz sine wave oscillator can be created with an opamp: https://www.nutsvolts.com/magazine/article/op-amp-cookbook-part-3

I understand now, thanks for all the help. Would the output in the picture be good enough?

 

but I'll see if I can replace the 555 timer

If you do that, you will need a real modulator.

Bob

 

He could use the modulator shown in post #6.

 

I agree that you are not modulating the carrier, instead you are blasting such a high level signal to the carrier oscillator that you are simply turning it on and off.
AM modulation is varying the carrier level, not simply turning it on and off. Didn't your teacher and text book say this?

 

Hello,

When switching a RF signal on and off, we do not call it AM modulation but OOK (on-off keying).

Bertus

 

I'm not turning the carrier wave completely off though. How can I make the output of the 555 weaker? I'm pretty new to this area, which is why I'm asking so many questions. Thanks for the help.

 

Hello,

When you put a resistor accross the C-E of the transistor, the oscillator will not be completely off.

Bertus

 

AM modulation is varying the carrier level, not simply turning it on and off. Didn't your teacher and text book say this?

How is going from 0 to 100% not varying the carrier level?

I would say that it is 100% modulated with a square.

Let's say it went from 10% to 90% instead. Would that produce any difference in the receiver other than the amplitude being only 80% of the original?

Bob

 

Switching the carrier on and off is mode A0, which is an amplitude modulation mode. Think CW now limited to some ham radio bands.

OOK on-off-keying is the same as A0.

 

Modulating with a square wave will give you a buzzing sound, not a tone.
Your 555 output should have a duty cycle of about 50%. Currently it looks like it is more than 90%.
The 555 output is too large and is almost completely killing the oscillator output. This actually becomes On-Off Keying of the carrier.
You need to pass the output through a capacitor to remove the DC component.

Your circuit is too simple to get good results but you will probably be able to hear it in the receiver.

Why exactly does the duty cycle have to be 50%?

 

Why exactly does the duty cycle have to be 50%?

A buzzer produces a perfect 50-50 squarewave that has lots of odd harmonics but no even harmonics. Even harmonics make it sound like a triangle waveform.

 

A buzzer produces a perfect 50-50 squarewave that has lots of odd harmonics but no even harmonics. Even harmonics make it sound like a triangle waveform.

Which sounds sort of like a flute if you roll off the higher harmonics.

Bob

 

I was wrong. A symmetrical waveform like a sinewave, squarewave or triangle wave does not produce even harmonics. A single vacuum tube and a single transistor squash half the waveform producing even harmonics.

I agree that a Morse Code beeper sounds better with a sinewave instead of sounding like a squarewave buzzer.

 

You need an AM modulator, feed your carrier in and modulate it with the 555 tone..

Here is one using an op amp, replace the OP amp osc with your colpits osc.