Welcome to this tutorial on RF interference and ground loops.

The 2 most common problems associated with leads are radio frequency interference and ground loops. The causes of these issues can be complex and difficult to diagnose and fix.

Caption - Radio frequency interference

All leads can behave as antennas, trapping Radio Frequency, or RF, interference from electromagnetic radiation. RF inference is caused by radio waves, adjacent electronic circuits and devices, and even the suns rays. If the lead is very long and the signal it carries very quiet, this can become a problem.

Caption - Ground loops and mains hum

Ground loops cause an additional unwanted low frequency signal in a signal path between devices and usually occur when there are multiple paths to earth. There are potentially a number of reasons why this may occur including differing circuit designs and equipment faults. Ground loops can not only cause audio problems, they can be a symptom of an unsafe device.

Unwanted low frequencies can also be generated by other conditions, such as the placing of mains leads adjacent to audio leads.

Caption - Eliminating RF interference, ground loops and hum

Before taking steps to eliminate problems, the culprit device, interconnect or power supply must be identified. Diagnosis should be slow and systematic, removing or exchanging each device in a connected system one at a time until the problem device is identfied.

Once identified, simply removing the device will proabably prevent you from using the system as you intended, so here are some of the ways to eliminate problems ..

• ensure that all devices are safely grounded through their mains power leads
• move audio leads away from power leads, especially looms
• are there any signs of damage to a device? investigate and repair it
• repair damaged cables
• use balanced interconnects throughout the signal path
• plug unbalanced interconnects into balanced sockets
• convert unbalanced signals to balanced signals with a DI box which features a transformer
• engage the 'earth-lift' switch on a DI box
• disconnect the earth core at one end of an audio lead by cutting or de-soldering it - insulate the core and let it hang out of the connector cover so it is visibly obvious what has been done

You should never attempt to solve an earth loop problem by disconnecting the earth in a devices mains power cable.

Caption - Dimmer switches
Dimmer light switches can be a source of interference in a studio. Replace any such switches on the same mains ring as your studio with conventional switches.

Caption - Thanks for watching

The script for this video, with accompanying images, can be found at projectstudiohandbook.com 

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