Wireless microphone tips

[Audiodude]

Everybody loves the convenience of cutting the cord and going wireless with your microphones. But getting them to work can sometimes seem like black magic. I put together this handy guide for people who are having problems with their wireless systems.

Wireless dropouts are not usually caused by defective hardware, but by improper use or installation. Before you declare your system defective, make sure you are doing all of these things:

Here are a few "best practices" tips for wireless:

- The most common cause of RF dropouts is improper antenna placement. Line of sight should be maintained between the antennas and the transmitters. If that's not possible in your rack, the antennas should be mounted away from the receivers, possibly up on a wall, balcony rail, ceiling, etc.

- Only use systems that are true diversity (two antennas) and frequency agile (have the ability to change channels if there is interference).

- Signal strength and operating range tend to drop off as the battery dies, so it's generally best to change your batteries at the beginning of every show / service, even if they aren't completely dead.

- Use an antenna combiner if you have more than two wireless systems.

- Use one of the databases provided online by the FCC or wireless mic manufacturers to choose frequencies that won't get interference from licensed transmitters (TV stations, public safety etc) in your area.

- Frequencies of multiple wireless systems must be carefully coordinated to avoid interference with each other. Simply having different frequencies is not enough. Usually, the best way to do this is to use wireless systems from the same manufacturer and series (so all Shure SLX in your case), and use frequencies that are already pre-coordinated not to interfere with each other. If you are mixing systems from different manufacturers or different series, consult an expert.

- True diversity (more than one antenna) is your best defense against dead spots and RF dropouts. In true diversity systems, both antennas must be connected for diversity to be achieved. They should be installed at least 9" apart, and at a 90-degree angle to each other. If they are remote-mounted, the cables connecting them to the receiver or antenna distro MUST be the same length.

- Also remember that human bodies are excellent absorbers of RF energy. Your wireless transmitter probably does not have enough "oomph" to power through an entire audience on their feet. If your antennas are in the back of a room, the middle of the pastor's back may not be the best place for beltpack transmitter. That forces the signal to pass through the pastor's body on its way to the receiver.

There are more, of course, particularly in large systems with a lot of units running at once, antenna distribution units, and remote-mounted antennas. If that's you, you would be wise to consult with a wireless expert (note: the salesman at your local guitar store likely does not qualify as a "wireless expert").

-Jeff B.

[TimmyP1955]

Good advice from Jeff.

I should like to add:

Until one becomes an RF expert (and who wants to go to that much trouble? :-), he should get all of his accessories (antennae, splitters, combiners, etc.) from the manufacturer of his wireless gear. This minimizes the scope for problems, insures that one will get the best support from the manufacturer and dealer, and eliminates the opportunity for buck passing when there is a problem.

If one must run long antenna cables, don't scrimp to save money - get the lowest loss cable that's available.

If one gets all his gear from one manufacturer, frequency coordination is a lot easier. Fire up their coordination software, tell it the city in which it is being used, tell it and what models/frequency ranges are being used, and it will designate which frequencies to use and which to avoid. (Always tell the software that more channels are in use than there actually are, so that there are some alternate frequencies in case of trouble.)

[GZsound]

Here's a wireless question.

Does changing frequencies make reception better? Do you get longer distances between the transmitter and reciever with different channels?

[TimmyP1955]

Depends on whether something is interfering with the original frequency, or whether the original is one that intermodulates with another unit that's in use.

[Audiodude]

In general, the lower the frequency, the better the propagation (the further the operating range, in other words). So a 50 mW transmitter at 300 MHz will have a longer range than a 50 mW transmitter at 900 MHz. However, the difference between two channels on the same wireless microphone system (626.500 MHz and 626.875 MHz, for example) will be negligible. As TimmyP1955 pointed out, the larger concern is whether or not two frequencies being used simultaneously will interfere with each other.

[TimmyP1955]

Darned near every wireless I've encountered (that was in use by a band) came with the transmitter gain set for the best signal to noise ratio, which often means at maximum. As such, with anything other than the most wimpy singer, the transmitter will overload and the sound will suffer as a result. Check your wireless carefully - both by looking at the meters, and by listening with headphones. IME most users fail to notice this.

One some mics the adjustment is a little switch, on others it's a little trim pot. On low cost units it's usually located in the battey compartment. On some of the units that have a digital display on the mic, the gain is accessed via a menu.

[rothwellsmith]

Will the frequency of the wireless mic have any effect on Feedback?

[TimmyP1955]

No. So long as the unit is working correctly, the RF frequency is irrelevant.