Lectrosonics UMCWB - Manual (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