Wire-Lists#10: 1 Tip to Identify Types, and 9 Ways To Prevent Wireless Mic RF Drop-Outs

Every wireless mic system has two parts: a transmitter connected to a microphone or source and a receiver that picks up the transmitted signal. Both of them have antennas - one to put out the signal and one (or more) to receive it. The area between the antennas is where most drop-out issues occur.

Start by identifying what kind of drop-out you're dealing with:

a) RF drop-out can be seen on the RF Meter. The meter will drop as the drop-out occurs. With Wireless Designer or with a DSQD receiver, the 10 second RF history display can help with identifying which channel/s are experiencing RF dropouts.

b) Pilot tone drop-out can be seen on the Pilot Tone Indicator. If the RF Meter shows sufficient RF signal, but the Pilot Tone Indicator shows a loss of Pilot Tone, try bypassing the Pilot Tone. If the audio is now acceptable, the problem is Pilot Tone drop-out.

c) Audio drop-out is your issue when you see a strong RF signal, and the Pilot Tone is present but audio is dropping out.

In all cases, especially when you suspect RF drop-out, the user should verify that there is no RF signal (or very little) with the transmitter off. RF interference can cause drop-outs that can impact RF reception.

If I'm reasonably sure that the problem is RF, what should I do?

Wireless RF drop-outs are most often caused by improper equipment installation, set-up or use. This graphic illustrates what Wireless Drop-out (in this example, on a VRM2) looks like on a Wireless Designer screen. You can see a few very quick drop-outs just prior to 45 seconds and a long drop out that begins just prior to 55 seconds. The squelch row shows a squelch condition as the RF metering dips, which is indicative of RF drop out.

You can save yourself a lot of time by taking the approach of Occamís Razor (i.e., the most obvious culprit is usually the problem) and confirming first that you donít have a defective cord, transmitter or receiver, or that you are not taxing the known limits of your system. If youíve already done that, consider:

1. The most common cause of RF drop-outs is improper passive antenna placement. You should be able to see the antennas and the transmitters when standing in the same place. Antennas should be mounted up and away from the receivers. If your signal is weak, try moving them closer together if possible or practical. Less than optimal antenna placement can cause low signal strength at the receiver or create unpredictable dead spots. If possible, using longer coax cables then employ in-line RF amplifiers to compensate, or use active antennas that have the amplifiers built in. If using amplifiers, only boost enough to compensate for the losses of the cables.
2. If using a handheld transmitter, be sure not to cover the antenna, which is near the bottom. We covered this in a recent Wire List. Instead, hold the transmitter closer to the capsule without covering it.
3. If you are using a belt-worn or bodypack unit with an external antenna, make sure that the antenna isn't bent or covered. It's very easy to get them caught in your guitar strap or wrapped in or under your shirttail. Not only is being bent bad for the antenna, but it severely hampers the signal it puts out. You can get shorter range and more drop-outs with a bent antenna. Even small bends can create issues (the unseen wires that make up the antenna can become stressed and broken from bending), so when in doubt, replace the antenna. They're only a few dollars, so it makes sense to have a few on hand for quick swap-outs.
4. Most radio energy (this is frequency dependent) is attenuated when traveling through bodies, walls or wood, and it can't go around corners (although it does reflect off of metallic surfaces). If your receiver is on one side of a room and your talent is on the opposite side, you're forcing the signal to travel through anything that is between them. Using an amplifier or a splitter usually wonít compensate for this; we explain why in our FAQ: Will an RF antenna amplifier or splitter give me an increase in wireless range or sensitivity?. Instead, place your transmitter and receiver in closer, unobstructed proximity.
5. If you have two or more performers on wireless, assign them frequencies as far apart as possible to avoid interference. Avoid channels in the 617-652 and 663-698 MHz bands, as the FCC now prohibits them for wireless microphones. The FCC outlines the specifics on their website, which is updated frequently as the regulations are refined.
   
   Just because you shouldn't tune to these bands doesn't mean it doesn't happen accidentally, so be aware of that possibility and double-check. We experienced more than one instance where a customer accidentally auto-tuned, experienced interference and discovered that their problem was that they were connected to a public safety band!
6. Multiple systems must be carefully coordinated to avoid frequency interference with each other. The best way to do this is to use wireless systems from the same manufacturer or set, and use frequencies that are already pre-coordinated (intermodulated) not to interfere with each other. There are a number of software programs that will make the required calculations and assign non-interfering frequencies. Our own Wireless Designer software is a great tool for use with Venue, Venue 2, DSQD, and Duet systems. This FAQ explains how you can troubleshoot intermodulation: How can I prevent RF inter-modulation interference? Do I have to use a specific brand program for each type of wireless system?.
7. Know your noise. Before you assume that the cracking sound you hear is static, first confirm that it is not the rustling of clothing or your wire rubbing against something.
8. Use covers to keep moisture out of your transmitters (we make several!). Moisture is nearly impossible to remove once it's gotten inside the unit's case. Moisture under components and in through-holes eats away at any copper in its path (connectors and wiring) and hampers any signal attempting to travel that path. This creates what is known as "path distortion," and this is difficult to self-diagnose without a spectrum analyzer or taking the unit apart. A good amount of drop-outs that are attributed to "noise" are really due to path distortion due to unseen corrosion.
9. Using more than one receiver (diversity) is excellent insurance against drop-outs. To achieve this, both antennas must be connected at least 6" apart, and generally more is better. Multi-path conditions that cause drop-outs are common in indoor environments, because that wireless signal will bounce off of everything metallic in that room. There are various ways you can position the antennas for your specific scenario, which we outline in this FAQ: What can I do to improve reception when my receiver antennas have to be close together?.

Being mindful of the type of drop-out you have as well as these tips can help you diagnose and prevent drop-outs. And as always, if you need us, weíre here! Give us a call, or troubleshoot your issue with other Fanatics on our Facebook discussion page.