Trying to build an AM transmitter.?

Question

I am trying to build an AM transmitter using a design by a guy named 5volt http://www.instructables.com/id/Make-a-simple-AM-transmitter/ (hit page down a couple of times, I'm not using the main design on there) I have a 1.0 MHz oscillator hooked up, a 220 Ohms resistor, and the correct capacitor but my transmitter won't work. I was wondering if this is because my oscillator has a supply voltage of 5 volts. I only have 3 1.5v batteries hooked up plus whatever comes out of my headphone jack. I was wondering if I should hook up another 1.5v battery and also if doing this might put too much voltage in my oscillator and short my oscillator out? Please help! Thanks!

Answer 1

That is not going to be an AM transmitter. FM is much more likely. Your power out is going to be milli-watts, at best. If you want an AM transmitter, the first thing you need to know is more theory, and the legalities of operating your own station. In a nutshell, 100 milli-watts maximum power, and an antenna no longer than 10 feet. Unless of course you wish to go commercial, and have several hundreds of thousands of dollars you want to spend on the project.

The oscillator in use will only produce an AM signal if you modulate the battery supply voltage, or it is designed to be a low power AM transmitter. Most likely, your modulation is going to produce a FM signal because you will causing the oscillator frequency to vary with the modulation signal being injected. Get a product fact sheet for the oscillator so that you have a better idea of what you are doing. That will help you to succedd, as well as help you to stay out of trouble. If you happen to cause interference with the radios, TV or any thing else with your transmitter, and you are caught doing it, you could get into a lot of legal trouble. You built it, you put it on the air, you are responsible for what harm it does. International law covers the use of transmitting devices. They are not toys, so do be very careful.

Answer 2

I've looked at the schematic and the explanation further down the page as you say.

What he is describing seems like it should work. You should not be having problems because you are using only 4.5 volts unless your batteries are almost dead. Putting 6 volts in there might not be such a good idea...

Aside from that make sure that the capacitor is the correct size and is placed correctly with regards to polarity. You have to make sure its only filtering out the DC and not the AC signal as well.

Also make sure you are using a large enough antenna and possible ground connection.