“How PSRR and other power-supply factors affect mobile-phone audio quality”
EETimes

Regardless of the protocol used by a mobile phone, whether GSM or TDMA, the RF transmitter switching creates sever noise for the power supply, as the RF power amplifier switches on and off at 217Hz. At each of these events, a hight current (tipically up to 1.7A) is drawn from the power supply, creating a sudden voltage drop through the battery’s equivalent series resistance (ESR)…

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