Lectrosonics UMC16b - Manual (Page 5)

UHF Antenna Multicoupler
Rio Rancho, NM 5
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
maintain a direct “line of sight” between the transmit-
ter and the receiver antennas. In situations where the
operating range is less than about 50 feet, the antenna
positioning 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 reflec-
tion can arrive at the receiver antenna along with the
direct signal. When the direct and reflected signals are
out of phase with each other a cancellation will occur as
the signals mix at the antenna input, resulting in what is
known as a “drop-out.”
At UHF frequencies, a drop-out usually sounds like a
brief noise burst, click, pop, or something similar. In se-
vere cases, 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 anrtennas are moved
to different locations.
Diversity receiver designs apply various circuitry to
select or combine two antennas to reduce or eliminate
multipath 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
for the maximum benefit.
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.
Accessory Antennas
The UMC16B will operate with any 50 ohm antenna
with a BNC connector, provided the antenna is tuned to
the same frequency band. Two unique models are of-
fered by Lectrosonics to help optimize recep-
tion in any location or installation.
The SNA600 is a versatile, collapsible dipole
antenna that provides a circular coverage pat-
tern and a 100 MHz passband. The elements
are tuned to frequency using a scale along
the feed line. A mounting stud and bracket are
included with the unit.
The ALP Series
LPDA anten-
nas are direc-
tional antennas
with 4.5 dB of
gain covering
a broad bandwidth
from 450 to 850 MHz. they
are constructed of FR4 fiberglass in
a rugged assembly and are available in several models:
ALP500, ALP620, and ALP650. Mounting options for all
ALP Series antennas include threaded rods and adapt-
ers to fit lighting equipment, tripods, mic stands and
attachment to building surfaces.
DIRECT S
IGNAL
INDIREC
T SI
GNA
L
DIRECT SIGNAL
INDIRECT SIGNAL
TRANSMITTER
PHASE
CANCELLATION
REFLECTIVE SURFACE
LECTROSONICS
Rio Rancho, New Mexico – U.S.A.
POWER
MULTICOUPLER