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frequency resonance of a LM358 op-amp

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jonovid:
this LM358 circuit is supposed to receive up to 3GHz from a cell phone.
please explain-

Kleinstein:
This is a rather bad circuit: 2 x 6.8 milliohm in series across the 9 V supply draws a lot of current.
If the resistors are meant to be 6.8 Mohm, the value is a bit high for the BJT base OP-amp.
With 100 nF from the antenna to ground there should ideally be not much AC voltage left. If at all the parasitic inductance and similar could make a difference, but they are not shown in the plan.
The plan is using the pin-out of the chip instead of the standard OP-amp symbols. This makes it hard to read - though it may be justfied if one would really follow the layout to include the parasitic efffects.


The LM358 is a plain, slow OP-amp. It may react to RF frequencies by rectification it the input nodes. How much is however hard to tell and it depends on the layout / manufacturer.

hans:

--- Quote from: jonovid on March 09, 2024, 12:34:39 pm ---to receive up to 3GHz from a cell phone.

--- End quote ---
No it doesn't

And the bulb is drawn like a Star of David, so stop the troll. Sorry, apologies, stress has gotten the better of me.

Andy Chee:
Found another LM358 phone detector

https://www.electronicsforu.com/electronics-projects/mobile-phone-detector-using-lm358

Even includes a PCB etching pattern!

Zero999:

--- Quote from: Kleinstein on March 09, 2024, 01:18:30 pm ---This is a rather bad circuit: 2 x 6.8 milliohm in series across the 9 V supply draws a lot of current.
If the resistors are meant to be 6.8 Mohm, the value is a bit high for the BJT base OP-amp.
With 100 nF from the antenna to ground there should ideally be not much AC voltage left. If at all the parasitic inductance and similar could make a difference, but they are not shown in the plan.
The plan is using the pin-out of the chip instead of the standard OP-amp symbols. This makes it hard to read - though it may be justfied if one would really follow the layout to include the parasitic efffects.


The LM358 is a plain, slow OP-amp. It may react to RF frequencies by rectification it the input nodes. How much is however hard to tell and it depends on the layout / manufacturer.

--- End quote ---
Yes, the resistors are probably 6M8, which is on the high side,  although the LM358 has fairly low bias currents so it's not that bad.


--- Quote from: hans on March 09, 2024, 02:04:53 pm ---
--- Quote from: jonovid on March 09, 2024, 12:34:39 pm ---to receive up to 3GHz from a cell phone.

--- End quote ---
No it doesn't

And the bulb is drawn like a Star of David, so stop the troll.

--- End quote ---
It's just a coincidence. The star just shows the bulb flashing. Don't let the Current Thing affect your judgement.

It's probably relying on the LM358 reifying the RF signal, which is unreliable. The circuit might work under some conditions, but most likely won't most of the time.

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