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How radio makes noise when cell phones is in active?

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Willen

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-How radio makes noise from cell phone? How 100MHz receiver can detects 900MHz cell phone friquency?
-Other amazing thing- My normal computer speaker also detects noise from cell phone. How this speaker amplifier detects cell phone friquency? Which parts of the speaker amplifier acts as a receiver antenna?
- any idea to remove to remove such bad noise from radio or amplifier?
 
Google "heterodyne intermediate frequency", "harmonic frequency" and "radio frequency interference".
 
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I have spent many days working to get RF noise out of audio amplifiers. Not easy.

A 'crystal radio' is not much more than a diode. The base-emitter junction in a transistor is a diode. It makes a broad band radio receiver. The input wires, power supply wires and the speaker wires are antennas.

In high end audio equipment beads, or RF chokes appear on the inputs along with small capacitors like 100pF. This makes a low pass filter to block AM radio. The RF filters may appear on any long wire inside the amplifier like wires going to the volume control.

The phone frequency is so high it does not take much wire to make a good antenna.

There are ferrite cores that clip on to power cores. Placing one on the input and one on the power wires might help. Keep it close to the amplifier.

Easy solution; keep the phone away from the amplifier.
 
It can be pulsating RF data packets that should obviously get detected and charge up the amplifier inputs to produce the audio level noise. I don't see any methods to avoid it because it is such a strong signal interference.
 
It can be pulsating RF data packets that should obviously get detected and charge up the amplifier inputs to produce the audio level noise. I don't see any methods to avoid it because it is such a strong signal interference.

And being an AM signal (i.e it's on and off during it's timeslots not like AM as we know it) it will be picked up by most electronic equipment.
 
There are multiple methods for cell phones. My "Sprint" phone does not cause my speakers trouble but the "Verizon" makes NOISE.
 
There are multiple methods for cell phones. My "Sprint" phone does not cause my speakers trouble but the "Verizon" makes NOISE.

I believe (but not tried it) that a 3G signal doesn't cause the interference a 2G phone does. Where I live I always get a healthy 3G signal, but still let my phone decide what to use.
 
The TDMA burst rate of GSM frames is 4.615 msecs. There are eight slots within this frame each being 0.577 msec.

The most common interference is caused by the frame burst rate at a frequency of 1/4.615 msec or 216.7 Hz with the 1/0.577 sec. bursts causing 1733 Hz buzzing with 216.7 Hz rep rate.

You sometimes can hear the intermittant 'buzz, buzz, -- buzz, buzz, buzz' when TV or radio newscaster's have their Blackberry too nearby. The strong GSM transmit bursts from the phone is getting into their microphone circuits.
 
It may also be the bluetooth. My cell phone comes thru radios when it is looking for bluetooth devices.
 
As Ron states, any non linear element in a circuit can act as a demodulator and at high frequencies a track or wire does not have to be very long to be a good antenna.
 
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