Picking up rogue radio station transmission signals through a PA system is really annoying and can be tricky to identify the causes. Some guitarists have a local FM station playing through their guitar amps. I have encountered an amateur FM station being picked up via very long XLR cable runs further extended by a long multicore and stage box.
- Close proximity of a source of radio transmission that can often be an amateur FM radio station.
- Long XLR cable runs where the cables are not well insulated and/or are run in close proximity to power cables, or tied tightly to a vertical mic stand that acts like a radio antenna.
- Some mics (including high quality ones) for some strange reason are susceptible to FM interference if by fluke the mic’s internal wiring ‘tunes in’ to the frequency of the radio transmission.
- With condenser mics, wireless interference can sometimes be increased when phantom power is sent from the mixer to the mic via XLR cable.
Suggested solutions include:
- Try to keep XLR cable runs as short as possible and avoid proximity to power cables. Do not lay long runs of XLR Cables parallel to power cables. Don’t tie the XLR cables tightly to vertical metal stands that can act like radio antennas.
- Have spare XLR cables available to swap out to see if different XLR cables stops the interference. Note that all the XLR cable supplied by Sydney PA Hire are high quality.
- The Rode M5 condenser mics are high quality and have worked flawlessly at many events. However, sometimes just using a different mic will remove the radio interference. We could supply alternative condenser mics such as Shure, iSK and Tascam.
- We also have the renowned Rode NT4 X/Y twin stereo mic that can be used in lieu of separate condensers on a twin mic bar.
- The phantom power/wireless interference issue is not well understood, but there has been some success in using phantom power sources at the mic and disabling phantom power at the mixer. Our Shure, iSK, Tascam and Rode NT4 condenser mics have battery powered phantom power integrated within the mics and don’t require phantom power from the mixer.
Unfortunately there is no easy fix as the radio interference could be caused by numerous factors. I suggest that the most practical options would be to have spare XLR cables to swap out, have at least one set of alternative condenser mics on hand to to swap out if necessary, this could include the Rode NT4 twin stereo mic. Experiment with using the battery phantom power option in lieu of phantom power provided from the mixer.
There is one other option that may not be practicable or cost-effective. We have phantom power enabled Sennheiser clip-on wireless transmitters that we often use with condenser mics when the mic positions need to be changed quickly between acts and long XLR cable runs would be trip hazards. This would require having compatible wireless receivers synced to the transmitters. With appropriate antennas the clip-on transmitter/wireless receiver setup can cover distances up to 100 metres or even further with direct line of sight.
If the radio interference is coming from a close or very powerful radio transmitter, remember that there might be no interference when you first test the setup, but the interference can start when the radio station turns on its transmitter (right in the middle of your show of course!)
