I have an antenna I made with about 2 feet of insulated copper wire, stripped at one end. The antenna is connected to the positive side of a 1000uF capacitor, using this circuit. I am using a 741 op-amp. The negative voltage for it comes from a separate battery with its positive lead connected to ground, and its negative lead connected to the op-amp. When I test the voltage of the output of this op-amp, it is constant. It has no frequency. This leads me to believe that my antenna has absolutely no signals coming from it. How can I fix my antenna?

I am also using a silicon diode.

  • \$\begingroup\$ Are you trying to make an AM radio? If so you'll need a tuned circuit of some form to get any sensible output. \$\endgroup\$
    – PeterJ
    Feb 17, 2014 at 5:10
  • \$\begingroup\$ The goal is to get any output at all. After that I will build a resonator. For now though, I'm not even getting static. \$\endgroup\$
    Feb 17, 2014 at 5:11
  • \$\begingroup\$ In your attached circuit, what gain are you expecting from the opamp, and why? When you say you get "no frequency", is the opamp outputting a value near one of its power rails? Do you have split-rail supplies for the opamp? What voltage are you powering it with? \$\endgroup\$
    – pjc50
    Feb 17, 2014 at 9:50
  • \$\begingroup\$ (Note that if you do succeed in building this system, the most likely thing you'll pick up is the 50Hz mains hum) \$\endgroup\$
    – pjc50
    Feb 17, 2014 at 9:58

1 Answer 1


I tried following your link, but there was nothing there. So my advice can only be very general.
1: 741 opamps are only good to about 20KHz, depending on how much gain you have (more gain = less bandwidth). While there are a few Low Frequency (LF) stations, you'd be better off using a different amplifier.
2: Opamps like the 741 use a "split rail". You need a positive supply, and a negative supply, and zero volts (or ground).
3: A capacitor on its own is not enough - you need a tuned circuit. Hopefully, this was on your missing circuit diagram. You need a coil and a tuning capacitor, in parallel. Adjusting the capacitor tunes the radio. As written, the only thing you might hear is electric noise generated by a thunderstorm.


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