Page 4 of 4

Single antenna vs. Diversity

Some ENG receivers utilize a single antenna. There is only one direct path from the transmitter to the receiver; and only one location for indirect (bounced) signals to be picked up. If, for some reason, the direct radio waves cannot strike the antenna (something blocking the signal path, such as a metal object), then there will be a momentary blackout of the audio, known as a dropout. Sometimes we are lucky, and an indirect radio wave will bounce off the ground or something and still manage to be received, but not always. Remember, actors are often moving; sometimes camera mounted receivers are moving as well.

Diversity systems deploy two antennas, and internally switch back and forth to whichever antenna offers the better signal. So chances are, if the direct radio signal misses one antenna, it may still be able to be picked up by the other antenna. Same applies to bounced signals. Even though the two antennas may only be inches apart from each other, it makes a big difference. Diversity systems have way fewer dropouts than non-diversity signals.

There are different types of diversity antenna systems. Cheaper wireless may have two antennas sticking up, but that is just to fool the consumer. The two antennas are wired together, which is better than only having one antenna.

Antenna diversity systems take it a step further. A comparator inside the reciever compares the RF signal from each antenna, and selects to use the stronger signal.

True diversity, which is featured in the better units, actually processes the RF signal into audio, and then compares which one is better. Essentially, there are two miniature receivers in each receiver.

Diversity units can be rack mount size, or miniaturized for ENG camera mounting

For diversity antennas to be fully effective, they should be separated at least a quarter wavelength (around 19 inches).

Some mixers prefer to remove the antennas from the receiver and connect them via a short length (5 to 25 feet) of RG-59 antenna cable in order to increase the likelihood of one or the other receiving antenna finding a clear signal, as well as to extend the operating reach of the system.

The advantages of diversity include less likelihood of RF dropout due to the direct or reflected signal paths being obstructed, as well as increased working range (based on the antenna placement).

The disadvantages of diversity can include having to deal with two antennas; audibly recognizable "switching" (a trait more common in the cheaper systems); and the chance of one of the two antennas locking onto interference.

Quad-Box

A quad-box or quad-pack consists of four individual ENG sized receivers, non-permanently housed in a compact case.

The case includes an antenna "splitter" (RF distribution amp) so that one single antenna (or two for diversity units) provides the feed for all four receivers.

Most quad-boxes also feature a centralized battery power supply that will "externally" power all the receivers.

Quad-boxes are convenient. Their only drawback is that sometimes better performance can be achieved by separating the receivers and placing them strategically closer to the action.

Receivers may be placed in different sites to optimize antenna line-of-site for each actor in the scene.

On reality television productions, the sound mixer often wears a custom apron or chest mounted utility bag that can house a portable ENG mixer along with multiple radio mics.

In some instances, two more radio mics are deployed as a stereo hop. The two transmitters take the audio feed from the mixing board and transmits the signal back to the camcorder. Many professional soundpeople will simultaneously back up their audio onto a portable digital recorder in their bag, just to be safe.