Choke inputs for RFI

If you cannot power down or remove cell phones, cannot control or predict whether phones will be near audio equipment, or just want an additional layer of security, a superb way to reduce or eliminate GSM interference is to add a ferrite core before a cable input. Ferrite cores, or beads, filter RFI (radio frequency interference) collected by a cable unintentionally acting as an antenna, while allowing audio signal to pass through.

When it comes to GSM buzz, not just any ferrite core will do. You must use one that has the correct number of turns and is made from material optimized for attenuating high frequency GSM signal, which can be anywhere from 800 MHz to 1800 MHz.

The best chokes for pro audio are manufactured by Fair-Rite and snap around a cable. They should be placed at the input.

In the context of wireless audio devices, GSM buzz seems to be more of a problem with mic and intercom belt packs. In some cases it may enter these devices via the cable connecting lavaliere or headset to belt pack. This cable outer diameter will fit 4.3 mm, so, if your lav cable is thinner than that you’ll need to roll some gaff tape or place additional insulation around the cable at the location where the core is placed to ensure a snug fit.

Please refer to the pictures. This simple and inexpensive device can save you from a lot of stress when you do your best and an annoying"bzzzzzzzzzzzzz" spoils your efforts.