Brian-Gaff wrote:


With the proliferisation of mobile devices running on the mobile phone
network its getting increasingly a annoying to listen to things on a good
old fashioned or even new fangled radio, without the noise occurring at some
point. Even from next door one can get it getting into the audio chain.
Anyone know if there is an easy way to stop it.



** There is no easy way.

In the old days a few
capacitors got rid of Radio China or Vatican City, but due to the high
frequencies of the phones and the spiky nature of the handshaking noise,
this seems not to work much. What is the mechanism. they cannot be tuned to
the r frequencies, so is it just straight diode type detection due to the
huge signal level?



** At a range of a few metres, the induced signal is hundreds of millivolts..
Rectification by a non linear component produces a small DC level and when the RF signal is 100% amplitude modulated at an audio frequency causes the buzzing noise. GSM phones are the worst.


Low level circuits like turntables, microphone inputs etc, seem to be the
worst, but I've also proved my Denon is picking it up from its speaker
cables.


** The standard technique is to reduce RF energy entering a device via input and output leads by making sure the shields are grounded to the metal case right at the connectors. A 10nF ceramic cap wired direct to chassis from the ground pin of the connector normally does the trick. The same can also be done with both speaker terminals.

I helps if all co-axial signal cables have woven shields.

If the device does not have a metal case, you are outta luck.


.... Phil