In the final chapter of this three-part series, we conclude our look at the factors that account for a full 80 to 90 percent of all wireless system problems, while also presenting solutions that will do the trick in most cases. The best solution is avoiding these problems from the outset. Certainly this won’t guarantee completely trouble-free operation, but the odds dramatically improve.

Digital Interference. Modern digital audio equipment, including processors, equalizers, controllers and other gear, operate at high clock frequencies that generate considerable RF noise (RFI). As a result, it’s not at all unusual for such equipment to interfere with wireless systems. Symptoms include low-level spurious tones, buzzing sounds, hissing and a varying noise floor. Digital interference can also cause an unexplained loss of range and other problems.

Although Federal Communications Commission (FCC) rules require that such equipment be tested to meet spurious emission standards, it’s a fact that not all units are indeed tested. In addition, loose covers and casings, warped metalwork, lax grounding and other mechanical shortcomings can greatly increase spurious RF emissions.

Even properly approved digital equipment, in good working order, may generate enough RFI to affect sensitive wireless receivers located nearby. When wireless interference occurs, one of the first things to do is to temporarily turn off digital devices to see if they are the source of the problem.

As a general precaution wireless receivers should be located as far as possible from digital gear. Often just moving the equipment a few rack spaces apart is enough to solve a problem. More severe cases may require separating the wireless power, signal and RF cables from those going to the digital equipment.

Using remote antennas with the wireless systems may also be helpful. And finally, try tightening up the covers on any offending digital gear and also adding a ground strap to the cabinet or other local ground point.

Lavalier Microphone Sound Quality. Lavalier (or “lav”) microphones can cause a number of different problems. A common user complaint is thin sound quality, which often occurs when the user has previously used only mics intended primarily for vocal applications. These mics generally boost low frequencies to make the voice sound warmer and fuller, but the omnidirectional mics normally used with wireless bodypack transmitter systems don’t have this boost and thus can sound noticeably different.

Another cause of “thin audio” from lavalier mics is RF interference. RF energy can “couple” into the mic cable and affect the preamplifier circuitry in the mic capsule. A high percentage of all lav mics exhibit this problem under at least some circumstances. If the voice quality and level varies when the mic and cable are moved around in close proximity to the wireless transmitter antenna and body, it is almost certain that RF interference is present.

In all cases, the manufacturer of the wireless system exhibiting this problem should be first contacted for specific recommendations. However, small RF bypass capacitors can be added to the mic connector to eliminate this problem; in most cases, 220 pfd chip capacitors placed between ground and the mic signal and bias leads will do the trick. Note that adding capacitors inside a transmitter rarely works as well.