[SOLVED] RF Emission from Piezoelectric Buzzer

[EricaS]

But I'm missing any idea how the phone circuit should generate RF.

So am I. Maybe the ringer generates RF by itself?

Did you actually try to detect RF emissions with a frequency counter? That's hardly possible.

Yes I did. With a Gooit frequency counter https://www.amazon.com/dp/B00ECTR008

Is there something else that can be used?

 

[Audioguru]

The Radio Shack piezo is a transducer, not a beeper or buzzer. it might produce two frequencies as a chord, or produce a sound that warbles between two frequencies. A piezo beeper or buzzer has 3 wires on the piezo and a transistor as a single frequency oscillator.
I think the recording of the song by Sia (there is no recording of speech) using the piezo transducer as a microphone sounds AWFUL about the same as the piezo used as a speaker, nothing but high audio frequency resonances. Its housing makes its main 3kHz or 4kHz resonance more than without a housing.

 

[Vbase]

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. The idea is based on some strange explanation how metal detector works.
What that you are doing is good. I wish you good luck and when you get some results I'll be happy to see them.

 

[EricaS]

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.

That's not true. I genuinely believe that my phone is bugged. I didn't want to mention that in the oscilloscope thread because I thought you would dismiss me as crazy.

I had no choice left but to tell you.

 

[Vbase]

I apologize for the bad assumption, I thought that you might be a little worried to tell us about your idea.
I hope you will be successful in your search for the eavesdropping method.

 

[vfone]

OK. Let's go to the original post:

"Is it possible for a pizeobuzzer ringer to emit audio as RF?"
The answer is NO!

So, knowing the answer what you are going to do now?

 

[betwixt]

...and your frequency counter is useless as an RF probe. You need a spectrum analyzer or a radio receiver capable of tuning to the tranmitter frequency.

You asked earlier about the resonant frequency in terms of half or quarter wavelengths to make the buzzer work as a secondary modulator. It depends on the diameter of the brass disc but assuming it is about 25mm across, the frequency beamed at it would be around 24GHz and the power level would have to be quite high. You would have two dishes of say 2m diameter pointed directly at you and in line of sight. If you can't see them you can dismiss the idea.

Brian.

 

[EricaS]

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?

I found that the polarity influences the expansion and contraction of the diaphragm:

From
https://www.murata.com/~/media/webrenewal/support/library/catalog/products/sound/p15e.ashx

I'm going to rent a spectrum analyser and search for RF.

 

[FvM]

I found that the polarity influences the expansion and contraction of the diaphragm

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.

The questionable point is about RF emission. There must be either an intenional RF generator 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. So the intentional RF generator is the only option.

There must be an RF oscillator circuit connected directly or indirectly to the the buzzer and it must be permanantly powered.

 

[EricaS]

There must be an RF oscillator circuit connected directly or indirectly to the the buzzer and it must be permanantly powered.

There's so much technical jargon in this article:
https://www.reddit.com/r/badBIOS/comments/2e3yuv/badbios_transmits_ultrasound_via_piezo_can/

"Most motherboards contain a piezo speaker that has always been connected to a logic gate output (the beep you hear on bootup). Any logic gate is capable of ultrasonic and/or VLF EMI (Very Low Frequency radio wavelengths). Connect that piezo element to a bi-directional gate and you have an ultrasonic communication system (piezo works both directions). VLF is a little trickier, but after working with the technology that Jane alluded to, very much within the realm of what they have been doing since before the PC came out."

Does this mean there is a "RF oscillator circuit"?
Or does this mean it can be done without one?
Or is that this part:

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.

That article also said this
"Piezoelectric transducers can receive and transmit ultrasound or VLF (very low frequency) radio."
Without mentioning anything about an oscillator circuit.
Please don't lash back at me I don't understand.

 

[FvM]

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).

 

[EricaS]

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).

Like i said earlier I'm 99.9% confident this phone is bugged.
And its got something to do with the grounding. Does the grounding mentioned in the article have any significance?
Maybe they swopped the chips and relabeled them or maybe it can do this already.

Do you have any idea what frequency ranges I should look in?
Is this going to be AM or FM?

 

[FvM]

As suggested, I would look for the ringer circuit power supply. If there's no permanent power supply, it can't work as a microphone transmitter. Same thing with the handset microphone or speaker (either of it makes a much better microphone than the buzzer) and the associated circuitry.

 

[EricaS]

The phone must be connected to the line for it to work. I know this much.
I disconnected the phone for a while because I don't like calls and they aggressively insisted I reconnect it.
So it doesn't work passively it needs a power supply.

Where should I measure the voltage? I don't have a clue.
Is it across the capacitor which I guess is the big red component?

- - - Updated - - -

One more thing:

Does the grounding mentioned in the article have any significance?
I know they aligned the grounding on the bugged phones.

 

[FvM]

I meaned voltage between pins of the ringer IC. The red capacitor will most likely have the telephone line DC voltage across it which is just normal operation.

I don't understand the grounding point.

 

[EricaS]

I meaned voltage between pins of the ringer IC.

Would you mind telling which component this is on the circuit because I have no idea.

I don't understand the grounding point.

Do you mean you don't understand what I mean or what the article means?

- - - Updated - - -

I have an Icom IC-R20, this together with HamRadio software can act as a spectrum analyser.
I'll test for RF later on today.

 

[D.A.(Tony)Stewart]

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!"

You can twist wires and wrap around a large Ferrite ring to reduce EMI and also use shielded pair.. Or better, get a piezo buzzer.

phones run off -48~-52V when on hook, any 600 ohm phone will drop the voltage, but high impedance monitor will not.

 

[FvM]

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.

I think the ground wire consideratuions in the article are arbitrarily meaningless. In any case, if there's a sender in your telephone, it won't need a ground wire beacuse it already has the telephone line.

 

[EricaS]

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.

Ok I see what you mean.
The chip is UTC31002.
**broken link removed**

I will measure later.

There is a third "IC" UTC1062 underneath inside the little metal "box".

 

[D.A.(Tony)Stewart]

Using a magnetic buzzer is like open close contacts to coil to move diaphram and is a cheap speaker with lots of RF noise hence shield needed on chip. Poor design.

What is the real problem?