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I'm developing an embedded system that uses telit gl865 modem to connect to a server using gprs.

I've noticed that the module makes a strange noise when connected. It's the same noise I used to hear in my old speaker when it was near the cellphone, and it happens when it connects to the server.

It doesn't happen with all the prototypes all the time. What could it be?

I'm afraid this will interfere with the rest of the system...

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    \$\begingroup\$ Have you tried contacting the module manufacturer? \$\endgroup\$ – Andy aka Jun 27 '15 at 10:50
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    \$\begingroup\$ what do you think is making the noise? is there an audio speaker in the system? \$\endgroup\$ – Techydude Jun 27 '15 at 11:49
  • \$\begingroup\$ @Techydude, there is no audio speaker. It isn't a loud noise, so I can't tell exactly qhere its coming from. It seems to be coming from the module itself, but it could be from the switching regulator nearby. But its only when the module connects, and it's clearly the cellphone-near-speaker noise... \$\endgroup\$ – João Ventura de Medeiros Jun 28 '15 at 14:56
  • \$\begingroup\$ @Andyaka I'm trying that too, still no answer \$\endgroup\$ – João Ventura de Medeiros Jun 28 '15 at 14:58
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Noise is mostly often caused by switching regulators that supply GSM. Bad components or assembly may be the cause. Please refer to : What might be the cause of high pitch sound coming from a switching regulator circuit for more information on supply noise.

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  • \$\begingroup\$ I'll look into it. but it's clearly that cellphone-near-speaker sound, and it isn't constant, only when connecting. \$\endgroup\$ – João Ventura de Medeiros Jun 28 '15 at 15:06
  • \$\begingroup\$ Then the switchmode regulator is only making that noise when it's under load - and GSM modems do draw a lot of current for those bursts of transmission. \$\endgroup\$ – Techydude Jun 28 '15 at 23:05

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