Is it OK to use a square waveform for the carrier my AM transmitter using TL072 OP-Amp?

Thread Starter

IsaacSesi

Joined Mar 23, 2015
3
phase shift.PNG AM transmitter.PNG

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
 

BR-549

Joined Sep 22, 2013
4,938
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.
 

Thread Starter

IsaacSesi

Joined Mar 23, 2015
3
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?
 

atferrari

Joined Jan 6, 2004
3,627
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.
 

kyka

Joined Jun 7, 2015
24
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
 

DickCappels

Joined Aug 21, 2008
6,079
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.
 
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