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I'm trying to get C3 to detect RF signals from a mobile phone. Amplify this signal to detect it using an LED. My main issue is simulating the antenna on multisim since multisim doesnt have an antenna!

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    \$\begingroup\$ CA3130 can't amplify signals above 10 MHz. You, however, need to detect 700-900-2400 MHz signals. This is your main issue. \$\endgroup\$ – Ale..chenski Dec 8 '18 at 4:11
  • \$\begingroup\$ could i use the BJT instead to amplify my signal? \$\endgroup\$ – Shawty Dec 8 '18 at 4:24
  • \$\begingroup\$ The simplest way is to detect the RF with a device sensitive to that frequency. Something as crude as a 1N21 diode would do that. If amplification is needed, a GaAs FET device can be used in a broadband circuit. Keep in mind component leads must be kept short. \$\endgroup\$ – AlmostDone Dec 8 '18 at 5:17
  • \$\begingroup\$ The CA3130 has FET input diffpair; apparently the RF causes some slight rectification in the FETs' source-well isolation-diodes. \$\endgroup\$ – analogsystemsrf Dec 8 '18 at 19:12
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The CA3130 is is being used far outside of its specifications.

It apparently does work in real life because of some non-specified behavior, but you can't get anything out of your simulator because it can't simulate the unspecified parts of the opamp.

If you want to test it, you will have to build it for real.

(I can't vouch for it really doing its thing, but the circuit is all over the internet. A lot of people seem to build it and recommend it. None of them says "don't bother 'cause it doesn't work.)


This site describes two cellphone detectors.

One is based on a diode detector, and the site discusses its performance a little - basically, poor and short range (centimeters.)

It doesn't mention at all how well the CA3130 circuit performs.

The only actual photo on the site appears to be of a third circuit for which no details are given.

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  • \$\begingroup\$ Any suggestions on how i could increase the range of this detector ? An article I read said " range can be increased by preamplifier stage using JFET or MOSFET transistor when used as an interface between the capacitor and IC" would this work ? \$\endgroup\$ – Shawty Dec 8 '18 at 21:18
  • \$\begingroup\$ I really don't know. The entire operating principle of that thing is "rape the specifications." The RF detection part is pretty much a mystery - it works for no good reason. How can you improve something that doesn't operate in any kind of normal mode? \$\endgroup\$ – JRE Dec 8 '18 at 21:37

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