Thanks but I am not trying to build someone elses. I can read a schematic and solder the components in to build theirs but I want to know how to build one from scratch....

From my ossilator circuit what do I have to create to take in the carrier wave and audio wave and output the modulated carrier....

Maybe the only way is the transformer method to get pure AM modulation?

I am still curious why product mixers won't work....
And curious how you design a circuit to product 2 input signals together?

I will try the attenuation diagrams but I am betting they will not give me pure AM modulation...

Thanks for your help I am looking for a quick circuit that I can add to the output of the ossilator circuit to modulate the carrier with pure AM using the signal from my audio port?

 

A transformer by itself won't do it, it is a linear component (usually). It can be part of a amplifier in such a way to vary the amps gain. Ultimately this is the cleanest way to modulate a signal.

Try what I suggested, put a capacitor and resistor in front of the base of your oscillator, and injected the audio there. The reason I think this will work is the variable voltage on the emitter will cause minor gain shift (I think).

The classic way I made AM transmitters during the CB craze of the 70's was to use a carbon mike, the type found in old telephones. Those are rare and hard to find nowdays, but a variable resistor (which is what they were) is perfect to vary the gain of the circuit they were in, so modulation was easy.

 

After looking your ideas over I'm a bit confused, but I think you want to take output from your computer sound card, modulate an rf signal and project it as radio. Am I right so far?

If so, your oscillator is probably okay if you used SPICE (and probably a design from somewhere else), but the 1k resistor seems unnecessary and your idea of mixing is simply not right.

If you want the audio wave from the sound card to modulate an rf carrier, you have to use a mixer. This can be done very simply. More if you want it.

 

Another point. There are two kinds of mixing: One is nonlinear and the other is linear. Linear mixing is used when you simply want to add two signals. An Op Amp adder will do that. This is usually used to mix audio signals. Another way to do this is simply join two similar resistors and input two signals at the ends of the resistors not connected to their junction. You can add as many resistors as you like and also have as many inputs, but there will be some attenuation at the output (the common junction of the resistors.

Nonlinear mixing -- which is what you need --occurs when you pass the two signals to be mixed through a nonlinear device such as a diode or a transistor. More on this if you want. I can show you a simple circuit that will probably get it done.

 

See post #10

Yes, this is what he wants to do.

I would be interested. I'm thinking unbalance a balanced mixer at the moment.

 

I realize that their are 2 types of mixers .... the ones that add 2 signals by just connecting the 2 signals with resistors (these add the signals ) (these where the ones I original had in my schematic but was wrong and should have been looking at the other kind of mixer)

The other is product mixers (which is the ones that I need to do )...They product the 2 signals together....
Since AM is m(t)* sin(2pi*f * t + theta) where m(t) is your audio trig function...etc This means you must product mix the carrier
sin(2pi*f*t + theta ) with the audio m(t).... enough with the math theory...

I understand why I have to "product mix the 2 signals together" to modulate AM wise.

But I am unsure how if the only way is using transistors and diodes then how? (nonlinear devices)

A transformer by itself won't do it, it is a linear component (usually). It can be part of a amplifier in such a way to vary the amps gain. Ultimately this is the cleanest way to modulate a signal.

Try what I suggested, put a capacitor and resistor in front of the base of your oscillator, and injected the audio there. The reason I think this will work is the variable voltage on the emitter will cause minor gain shift (I think).

The classic way I made AM transmitters during the CB craze of the 70's was to use a carbon mike, the type found in old telephones. Those are rare and hard to find nowdays, but a variable resistor (which is what they were) is perfect to vary the gain of the circuit they were in, so modulation was easy.

I know the transformer by itself won't do AM but what I made before was an AM transmiter with a transformer and a crystal ossilator in parrell on the primary side and the other side was plugged into my audio port of my computer the audio would change the magnetic resistance of the inductor which would change the amplitude of the crystal ossilator ... work fine for me. What I just got from your post is this method of using transformers is the cleanest to do AM.... (seems to simple to be true)

As for put a capacitor and resistor in front of the base of your oscillator, and injected the audio there ( could you give me a picture of what I should do for this?)

And do they still sell carbon mikes? because that would be an easy solution to modulate AM all I would have to do is put the mic at the output of the ossilator.

Nonlinear mixing -- which is what you need --occurs when you pass the two signals to be mixed through a nonlinear device such as a diode or a transistor. More on this if you want. I can show you a simple circuit that will probably get it done.

After looking your ideas over I'm a bit confused, but I think you want to take output from your computer sound card, modulate an rf signal and project it as radio. Am I right so far?

If so, your oscillator is probably okay if you used SPICE (and probably a design from somewhere else), but the 1k resistor seems unnecessary and your idea of mixing is simply not right.

If you want the audio wave from the sound card to modulate an rf carrier, you have to use a mixer. This can be done very simply. More if you want it.

I realize that I don't need a few things like the 1kohm resistor. And I need to some how create a product mixer that takes the carrier and audio from the soundcard and products the 2 together.
Seems by the previous posts the only way to make product mixers is by using nonlinear devices (like transistors, diodes ) but how that is the question?

Thanks for any help on this

 

Unfortunately I don't think they still make carbon mikes. You might be able to find an old one, they used to be in every telephone in the world. They are simple, but their freq response is atrocious.

 

Mathematics, you could use an IC such as a 1596. Google it and find the application notes. I'd show you how to use diodes or a transistor, but I forgot how to put pictures on my posts.

A passive mixer consists of a ring of 4 diodes and two transformers and the output has to have a filter to get rid of all the unwanted harmonics. This is a complicated method.

You might try using a single common emitter amplifier. Inject the rf into the base and the audio into the emitter. The output is the collector and you have to follow it with a filter to get rid of harmonics.

 

Hello,

You could also have a look at the LM13700 IC.
In the datasheet there is an AM modulator written.

The AD633 is also a ringmodulator like the MC1596.
Here is an audio example:
http://www.musicfromouterspace.com/analogsynth/RingModulator/RingModulator.html

Greetings,
Bertus

 

Mathematics, you could use an IC such as a 1596. Google it and find the application notes. I'd show you how to use diodes or a transistor, but I forgot how to put pictures on my posts.

A passive mixer consists of a ring of 4 diodes and two transformers and the output has to have a filter to get rid of all the unwanted harmonics. This is a complicated method.

You might try using a single common emitter amplifier. Inject the rf into the base and the audio into the emitter. The output is the collector and you have to follow it with a filter to get rid of harmonics.

First , I want to make the modulator circuit from scratch NO IC chips...

This limits me to the passive mixer or common emitter amplier of your post in quotes...

Curious if you have a schematic you could post for the passive mixer and common emitter amplifer..... for the AM modulation

Thanks

 

I've already posted a design I've never built, you'd get to be the first! Of course, it might not work either.

Did you ever look up the balanced mixer schematic I linked to? A simple diode setup would do the same thing.

 

Hello,

Did you have a look at the balanced mixer using transistors, I gave you in a former link:

Greetings,
Bertus

 

I've already posted a design I've never built, you'd get to be the first! Of course, it might not work either.

Did you ever look up the balanced mixer schematic I linked to? A simple diode setup would do the same thing.

Do you mean this attenutation/transistor diagram
http://forum.allaboutcircuits.com/attachment.php?attachmentid=14723&d=1261884320

If so I am going to try this when I get home in a few days it should work in theory
Except what resistor values should I use and what capacitor values / transistor should I use...?
Also is VCC the 9volt battery of the ossilator circuit or is it another external battery if external what is it's value...

 

Yep. Bertus design look more promising. You could replace the crystal oscillator with yours, and use the rest. Basically it is a differential amplifier.

 

Well , I tried your attenuation transistor circuit... wasn't to bad it works but it didn't give me to much range though.... (at least I don't think but I am still working some of the bugs out on this one filtering harmonics ,...etc etc )

As Bertus's design above
Question , I am unsure what components to take out/leave in so I can swap his crystal ossilator with my ossilator circuit ?

Here is what I am thinking but I know it is somewhat wrong
attached is the picture .... circled is what I am taking out in place of my ossilator????

 

forgot to attach

 

Hello,

You can put your oscillator at the place of the circled parts.
You will need the coupling capacitor to block the DC from the oscillator.

Greetings,
Bertus

 

First , I want to make the modulator circuit from scratch NO IC chips...

This limits me to the passive mixer or common emitter amplier of your post in quotes...

Curious if you have a schematic you could post for the passive mixer and common emitter amplifer..... for the AM modulation

Thanks

I hope this attachment works....

... upon edit, I see that it did. The transformer is just a toroid with a 2:1 stepdown ratio. Pick a small capacitor and put an even smaller variable cap in parallel with it. Then calculate the L from: f=1/(2*pi*sqrt(L*C))

f is your radio frequency.

 

Thanks for all that I am curious about one thing when I was studying transistors on the allaboutcircuits book....

It is in the attached picture....

The transistor can amplify the total sinewave at the base if their is a suitible foward basised voltage to keep the transistor from going into cut off or saturation ..... (in the picture the base sine wave is amplified and inverted)

What I want to know is what would happen if the 15volt dc emitter-collector supply voltage was an AC sinewave voltage? ( then would the base wave by am modulated/amplified instead of just amplified )

Would the output from combineding the base sinewave and the ac sinewave voltage be equivalent to Amplitude modulation of the base sinewave.... Would it be in theory the product of these to waves ????

If the common-emitter inverting is going to be a problem then how about the same question but using a common-collector ???

Or will this also somehow effect the frequency/period of the output wave....

Curious because in the AAC book they never talk about if the voltage connect to the emitter-collector is sinewave....
And weather being sinewave will effect the frequency/period of the output wave?

Thanks for any help
And when I get a chance I will build the above schematic you just gave me.

 

Does anybody know the answer to my above post ?
Curious to know...
Since the AAC internet book only does examples when the high voltage/current battery is DC and not ossilating...

Thanks if it is equivalent to AM modulation then a one transistor could be used as a product mixer...

Thanks