But I'm missing any idea how the phone circuit should generate RF.
Did you actually try to detect RF emissions with a frequency counter? That's hardly possible.
So am I. Maybe the ringer generates RF by itself?
Yes I did. With a Gooit frequency counter https://www.amazon.com/dp/B00ECTR008
Is there something else that can be used?
When I look at this thread and the one with the oscilloscope I get the impression that you are a 'bright private detective' who tries to invent a phone listening device (bug) using the buzzer.
I've inspected about 70 of these phones (at the office and a department store) all the clean phones have the negative lead (black wire) of the ringer connected to the positive terminal on the PCB and the positive lead (red wire) connected to the negative terminal of the PCB. The phones that I suspect are bugged have the polarity correct, I.e. red wire to positive terminal and black wire to negative terminal.
I believe its no coincidence that the bugged phones have different polarity connection than the clean phones. But some have said this means nothing, is that true?
Yes. I believe everyone taking part in this discussion knows well about the operation principle of a piecoelectric transducer. Also that it's essentially bidirectional and can act as a sensor as well. This part of your theory hasn't been doubted. The bad microphone point is about sound quality but not the principle possibility to use the buzzer as microphone.I found that the polarity influences the expansion and contraction of the diaphragm
There must be an RF oscillator circuit connected directly or indirectly to the the buzzer and it must be permanantly powered.
or or an audio generator with extremely fast edges to generate considerable RF amount. But the buzzer sound generator is only active when the buzzer sounds and drowns out anything else.
The "bad bios" article has a valid point. A complex digital IC connected to the buzzer (e.g. on a PC motherboard) could implement a RF generator circuit. But that's a completely different topic. Your phone has a simple 8 pin ringer IC connected to the buzzer, driven by a rectifier that presumly powers it only when the high ring voltage is present (you can verify this assumption with a mutimeter).
I meaned voltage between pins of the ringer IC.
I don't understand the grounding point.
Hello
Is it possible for a piezobuzzer ringer to emit audio as RF? NO so it must be magnetic type, then YES
Here are some pics of the buzzer. (Black object).
View attachment 117277
View attachment 117276
Someone once had this to say:
"I have no direct experience but a change in the position of the diaphragm will certainly change the impedance of the coil which will affect both its Q and resonant frequency. A nearby transmitter may well have a detectable audio modulation of its frequency or power. That is after all how a metal detector works!"
The very simple telephone circuit has only two ICs, a 16 pin DTMF dialer and a 8 pin ringer IC. I was talking about the ringer.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?