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

Discussion in 'Wireless & RF Design' started by IsaacSesi, Dec 9, 2015.

  1. IsaacSesi

    Thread Starter New Member

    Mar 23, 2015
    3
    0
    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
     
  2. BR-549

    Well-Known Member

    Sep 22, 2013
    1,981
    388
    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.
     
    IsaacSesi likes this.
  3. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    761
    TL072 Is good for much lower frequencies, no MHZ.
     
  4. IsaacSesi

    Thread Starter New Member

    Mar 23, 2015
    3
    0
    okay so what would you suggest that i do? any particular components which could be of help?
     
  5. IsaacSesi

    Thread Starter New Member

    Mar 23, 2015
    3
    0
    so what alternatives can i use?
     
  6. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    761
    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.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,779
    932
  8. kyka

    New Member

    Jun 7, 2015
    22
    1
    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
     
  9. DickCappels

    Moderator

    Aug 21, 2008
    2,648
    632
    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.
     
Loading...