Hello ,

can we amplify a small signal of 433Mhz by an amplifier based on an lm358 (which its 700khz of BW) ??
I got this question while watching this video (in the video the guy went even further than my question; he made it into a mobile phone wave detector) ;

Thank you in advance for your answers.

 

No. Open-loop gain falls off with frequency. At 1MHz the gain of LM358 is 1.

 

No. Open-loop gain falls off with frequency. At 1MHz the gain of LM358 is 1.

But the Guy in the video success to detect a smartphone's frequency whit this lm358! How it can be possible ???

 

I did not bother to look at the video. There is a lot of nonsense posted on YouTube.

 

I did not bother to look at the video. There is a lot of nonsense posted on YouTube.

Ok , thanks for repli.

 

A modulated RF waveform is complicated and you are not yet sophisticated enough (not a criticism) to see from the video just how the LM358 is being used. If you can extract the schematic from the video and show it to us we might be able remove the fog of mystery surrounding this. As @MrChips said, we have better things to do than to watch this particular video.

 

They will let anyone make a yourtube.
The right half of the LM358 is being used as a voltage comparitor. That is simple and we can see how it works.
The left half is ...... I lack the words ..... not working how he thinks. Amplifiers in the presents of strong RF can work as an AM detector. I have built may recording studios in radio stations. It is common for as audio amplifier to detect strong RF signals. The diodes in the amplifier will work like a crystal radio. The first amp is not amplifying the signal. What I think is that the amp is not fast but the diodes in the amp are.

IMO RonSimpson

 

Hello,

If you want some more serious reading about RF detectors, have a look at the following pages:
https://www.maximintegrated.com/en/design/technical-documents/app-notes/5/5085.html
https://www.reddit.com/r/rfelectron...f_detector_circuit_for_listening_devices_and/

Bertus

 

The video was produced in the same country as all the other You Tube nonsense videos.

 

The video
from a brief look I must admit, is valid,

The circuit is a simple "power detector",
The coil / wires, convert the radiated signal, to a voltage,
the front of the LM358, has, like most silicon circuits, an inherent diode,
and this forms a rectifier.

The LM358, makes a good low frequency amplifier,
which then provides the voltage to drive the LED.

 

But the Guy in the video success to detect a smartphone's frequency whit this lm358! How it can be possible ???

BS!

 

Many You Tube videos are from that country and are fakes.
But the smartphone signal is very close to the LM358 then the base-emitter of its input transistor can be overloaded and rectify the signal like a crystal radio then the rest of the opamp circuit amplifies the DC enough to flicker an LED.

 

But the Guy in the video success to detect a smartphone's frequency whit this lm358! How it can be possible ???

If the LED was flashing at RF frequencies, then that would be GHz,.. !!
The led is showing a RF signal thats been rectified.