Multiple Systems: Audio Visual, Video, Projection, Presentation Rental AV Equipment

Multiple Systems

When a number of multiple systems are used in a given location it is a common practice to use antenna combiners to eliminate the antenna Farm. Antenna amplifier/combiners are a convenience item that allows a single pair of antennas to feed multiple receivers.

Common TV splitter/amplifiers are not recommended for wireless microphone installations because the have too wide of a frequency range (usually 50-216 MHz) which can seriously degrade the performance of the microphone receiver. The extra wide response can create problems with front-end overload and de-sensing due to the high-output broadband signal level. In addition, most commercially available TV splitters are designed for 75 Ohm operation, and most wireless microphone receivers are designed for 50 Ohm operation. The resulting impedance mismatch can create a loss of signal by as much as 3 dB. By contrast, narrow-band devices designed for wireless microphones are generally preferred in order to match the input impedance, and keep unwanted signals out of the system in the first place.

Most splitter/amplifier devices made for wireless microphone systems with two inputs and eight outputs (diversity) and can be daisy-chained to a second splitter on the each of the eight outputs allowing up to 16 receiver/transmitter combinations to share a single pair of antennas. When using this type of system it is important to use a remote antenna with some degree of gain as a Ľ wave whip is generally too much of a compromise to provide good results. A high-quality remote antenna such as a Log, Yagi, or 5/8 wave is recommended. In addition, the antennas must match the frequency range and input impedance of the receivers to be effective. The main disadvantage to this technique is that it tends to be costly because of the relatively high cost of the splitters, but it’s well worth it. Here are a few tips that can help eliminate common problems when using combined systems:

All frequencies should be checked for compatibility prior to installation using a suitable intermod program (discussed later).
Select an antenna whose frequency range corresponds to the operating frequencies of each receiver/transmitter combination. Secure the antennas in a location that is as free from obstructions as possible.
Select an appropriate high quality active splitter/combiner insuring that the unit is designed for wireless microphones, and is not a common TV type device.
Use a high quality coax with the proper impedance match to the antenna and receiver, and terminate all unused outputs with termination resistors in the splitter to keep the overall gain consistent from receiver to receiver.
Never use excessive amounts of feed-line from the antenna. Most quality wireless systems have plenty of range. Placing the antenna closer to the transmitter at the expense of long cable runs deteriorates signal level by the loss in the coax cable. This can be as much as 6 dB over a run of only 50'. In situations where there is no alternative, a quality line amplifier may be used, but care should be exercised to select a very low noise device made for wireless microphones.
Don’t skimp on the antenna because a good antenna system can really become a valuable tool in any wireless system. In addition, use as few connectors as possible, because each connection can cut as much as 1 dB from the signal. We recommend using high-quality coax cable with copper braid and copper center, and quality connectors such as Amphenol silver plated type.