The 2 Most Wanted Enemies of RF - Avoid at all Cost
Whether it's friends and politics or beer and wine, there are some things in life that should never mix. In the world of wireless, there are two entities that should be avoided at all costs when operating your rig - two major enemies of RF if you will. Read on to discover what they are and how to avoid interference as a result of them.
Enemy Number 1 - Metal
Radio frequency signals are reflected or reduced in level by metal. One very common and avoidable cause of RF dropouts occurs when receiver antennas are hidden inside a metal rack. Unaware of the issues metal can cause, some engineers proceed with installing rack ears to a receiver, securing the receiver into the rack, and then attaching antennas to the rear of the receiver. The problem is, once the rack doors are closed, the wireless mic RF signal is effectively blocked from reaching the receiver. A better approach is to use the correct antennas outside of the rack and place them in line-of-sight with the microphone transmitter.
For metal to be a problem, it doesn't even have to be solid. The metal can be a chain link fence or even a metal grill. If the openings or holes are smaller than the RF wavelength, then the signal will be blocked. For example, if an RF signal at 500MHz has a wavelength of 2 feet in length and the apertures of the fence are far smaller, then despite the holes, your chain link fence might as well be a solid metal wall. The RF signal will simply be unable to pass through it.
Enemy Number 2 - Salt Water
RF enemy number 2 is salt water - primarily from the human body. Cast your mind back to school science lessons, and you'll likely recall that our body mass is made from up to 80% water. This body water contains salt, which attenuated RF signals as they pass through.
Consider an installation at a local music venue. The wireless receiver is located at the rear and placed on a shelf next to the mixer. The wireless system is tested before the audience arrives for the show, and it works perfectly. Then a few hours later, an audience of 500 people is ready for the band to kick off, and just as they do, the wireless system drops out. Why? Because the RF signal from your transmitter now has to pass through 500 containers of salty water before reaching the receiver. The answer is to elevate the receiver antennas above the audience to achieve a clear line-of-sight with the transmitter.
A similar problem can occur during a panel discussion event, where each speaker is equipped with a wireless body pack transmitter and a lapel mic. If the transmitters are positioned poorly – say in a back pocket – the body could obscure the transmitter and attenuate the signal if the speaker were to sit down.
The Bottom Line
Running a wireless system can seem complicated, but like most things, it's easy when you know how. The key learning from RF enemies one and two is that maintaining line-of-sight with your receiver and antenna is essential. By avoiding key wireless faux pas and by understanding the fundamental principles of RF, taking control of your rig becomes much more straightforward.