Why did speakers used to make a strange noise when a phone is about to receive a message? Also, why that doesn’t happen as often now (little to no instances)?

Question

Why did speakers used to make a strange noise when a phone is about to receive a message? Also, why that doesn’t happen as often now (little to no instances)?

In: 1651

Answer 1

The phenomena occurred during the 2G era. 3G and later phones use spread spectrum technologies (CDMA, OFDM), which distribute energy over a wider band. I.e., the signal before narrowly concentrated its energy in a single band (let’s say over 0.2MHz). This spike was picked up by the amp driving the speakers. Now, the energy is distributed over a fatter channels (let’s say over 20MHz). Instead of a spike, it’s more like a blunt mallet. This leads me to believe the problem isn’t with the oscillator that tunes to the frequency band (after all, 5G reuses 2G bands) but with the distribution of the energy in that band.