Hello, I am very new to practical electronics stuff and I am trying to build an AM transmitter using TL072 OP-Amps and no inductors. I wanted to generate a 1MHz carrier wave with one OP amp and make a modulator with another OP-Amp. After reading on OP amps, i decided to generate a sine wave by Building a Phase Shift Oscillator. However after trying unsuccessfully to get 1MHZ, I Googled and read that the Phase Shift Oscillator is not meant for high frequency applications, as the reactances of the capacitors become negligible. So i decided to generate a square wave instead for my carrier using a schmitt trigger, and I was able to generate 1MHz (from my Proteus simulation). i haven't built the entire circuit yet. What i want to know is if the AM transmitter circuit will work fine with a square waveform as carrier. Thanks

 

No. You can use a square wave for your reference, even modulate it, but before you use it as a carrier, you must filter and condition it.

Unless you want people that listen to AM radio hunting you down.

 

TL072 Is good for much lower frequencies, no MHZ.

 

No. You can use a square wave for your reference, even modulate it, but before you use it as a carrier, you must filter and condition it.

Unless you want people that listen to AM radio hunting you down.

okay so what would you suggest that i do? any particular components which could be of help?

 

so what alternatives can i use?

TL072 Is good for much lower frequencies, no MHZ.

 

so what alternatives can i use?

I am not qualified to advice on that. Had I to do something like that I would start by looking for a crystal oscillator.

I recall implementing a simple one (10 MHz) with a transistor, a crystal and few more components.

I insist, I am not experienced on all that.

 

http://www.jameco.com/webapp/wcs/st...7861_-1?avad=182414_fa182c26&source=Avantlink

 

First and foremost, you need a license to transmit at the AM band.

Now, the TL072 is not suitable for these frequencies and, actually, most cheap widely available opamps are not. This is usually done with a transistor but building a high-frequency power amplifier is not an easy task.

I suggest you to look at something like the following. It uses the famous 555 timer and some other simple components.

http://electronics-diy.com/am-radio-transmitter-using-555-chip.php

 

Wait a minute, IsaacSesi is from Ghana. Laws regarding unlicensed radio transmitters vary greatly by jurisdiction. If your power is very low and you avoid international distress signalling frequencies for your carrier and its odd harmonics, you should be ok. It would probably be better for your to look up the requirements for your jurisdiction rather than taking legal advice from internet forums like this.

Technically, you can use square waves -the difference between using square waves compared to a pure sine wave is that some of your transmitter power will go into odd harmonics of your carrier frequency.