I am making a small AM Transmitter for short wave band. It needs to transmit voice from a tape player with a range of about 20 meters. I thought the easiest way to modulate the signal would be to use an op-amp to combine the carrier and audio input, but since I don't have any and the nearest electronics shop is far away I decided to combine the signals just by joining the wires and use a power mosfet to amplify it. I know a little about electronics and know this might be a stupid guestion, but could someone verify if this should work. The crude picture attached should clarify what I mean.

Any help will be appreciated
Thanks

 

Hello,

I think your schematic will not work.
You are adding the signals.(superposition).
Take a look at the modulation techniques page from the EDUCYPEDIA.
http://www.educypedia.be/electronics/modulation.htm

Greetings,
Bertus

 

Thanks Bertus!

I spent time reading more about modulation techniques from the link you provided. Then I modified my circuit and now it seems to work just fine. Now it first creates and amplifies the carrier wave and then modulates using normal bipolar transistors.

 

This is my favorite AM transmitter. Adjust the inductors to your application. You can capacitively couple your carrier into the base of the left-most transistor in place of the crystal.

This should allow good, clean, amplitude modulation. Its based on the Gilbert Cell.

http://www.techlib.com/electronics/amxmit.htm