Lectrosonics UMCWB User Manual download pdf (Page 9)

UHF Diversity Multicoupler

Rio Rancho, NM 9

Antenna Use and Placement

Try to position the antennas so that they are not within 3

or 4 feet of large metal surfaces. It is also good to main-

tain a direct “line of sight” between the transmitter and

the receiver antennas. In situations where the operating

range is less than about 50 feet, the antenna position-

ing is much less critical.

A wireless transmitter sends a radio signal out in all

directions. This signal will often bounce off nearby walls,

ceilings, metal surfaces, etc. and a strong reﬂection can

arrive at the receiver antenna along with the direct sig-

nal. If the direct and reﬂected signals are out of phase

with each other a cancellation will occur as the signals

mix at the antenna input. The result will be a “drop-out.”

A drop-out usually sounds like a brief noise burst, click,

pop, or something similar. In severe cases, it may result

in a complete loss of the carrier and the sound. A drop-

out situation may be either better or worse as a crowd

ﬁlls and/or leaves the room, or when the transmitter and

receiver antennas are moved to different locations.

Diversity receiver designs include a method of select-

ing or combining two antennas to reduce or eliminate

drop-outs. The antennas must be placed at least a half

wavelength apart to achieve a noticeable reduction in

drop-outs, or better yet, several feet apart.

It is generally best to use two of the same type anten-

nas on a diversity receiver, as some designs combine

both antenna signals into a single receiver with a phase

correction between them to maximize the resultant RF

signal. If one antenna signal is signiﬁcantly stronger

than the other, the signal from the weaker antenna will

do little to prevent multipath drop-outs that occur at the

stronger antenna.

The diagram below depicts a classic multipath drop-out

situation. In some diversity designs, a second antenna

in a different location is selected instead of the ﬁrst an-

tenna, following the logic that a multipath drop-out is not

likely to occur simultaneously at both antennas. Other

designs combine the two antenna signals and control

the phase of one them to make sure they always add to

each to provide a stronger signal.

DIRECT SIGNAL

INDIRECT SIGNAL

DIRECT SIGNAL

INDIRECT SIGNAL

TRANSMITTER

PHASE

CANCELLATION

REFLECTIVE SURFACE

1 2 3 4 5 6 7 8 9 10 11 12

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Lectrosonics UMCWB User Manual Page 9

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