Audible GSM noise

For a year I've had a Nokia E71 operating on AT&Ts GSM network. And I've been plagued by noise coming from other devices when my cell phone is close to the other devices. Is there anything to be done about this besides just moving the cell phone to the other side of the room? Much thanks, I wasn't able to find to much about this on Google, which surprises me because this must be a common issue.

Not really. Better shielding on the wires and enclosure.

The blipblipblip noises from a GSM phone are the TDMA packets being sent which have a 4.615ms gap between packets. This causes a 0.5W 217Hz signal to be induced into any nearby wires like your speaker cables.

I've noticed it mostly when I have the phone next to the amplification device rather than the cables.

For example, if someone puts their phone near my empeg, its speakers, or the wires, no problem. But as soon as they put their phone in a backpack in my car's trunk where the amps are, we get the noise.

The only way to prevent it would be to figure out a way to improve the RF-shielding around the amplification device that's susceptible to the interference. (RF-shielding the phone would work too, but would make it so that you can't receive calls.)

I can attest that cubicle walls provide no isolation at all.

I'd have to agree with you there. In one of our projects we had an audio amplifier IC that when powered would emit a terrible GSM buzz whenever a transmitting phone was within 6 feet of the PCB. But we redesigned it to use a more noise immune amp and now do not exprience the problem.

It has a lot to do with the topology of the amplifer as well as the signal routing. A differential signal all the way to the transistors, fets, ICs etc will help immensely. In our case we are using a 1 watt digital amplifer with single-ended connection but were using a BTL (bridge tied load) device.

Stu

You'll also do well by simply adding RF shunt caps around your sensitive nodes. Providing a path for the RF energy to ground - a 27pF 0402 cap is perfect for low-band GSM - can be a very simple solution to the problem.

Now imagine doing this where the transmitter and antenna are millimeters away and not moving