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Antennas
The antennas supplied with most wireless products
are omnidirectional. These are suitable for both
point-to-point and point-to-multi-point applications. If
additional transmission range is required it may be
possible to use directional receiving and /or transmitting
antenna(s). Note that although diversity receivers are
always preferred it may not be necessary (or practical) to
use directional antennas on both antenna inputs for point-
to-point. Since the transmitter and receiver locations are
assumed to be fixed in this application, multipath variations
should be minimal once the equipment is set up.
Maximum range of point-to-point wireless
The practical range for most of these systems in point-
to-point applications is comparable to their published
range in normal usage. For standard wireless systems this
ranges from about 150 ft. to 800 ft. depending on various
conditions. Directional antennas may boost these ranges
by 50%. Good line of sight and the normal precautions for
frequency selection are assumed.
The maximum range system employs IEM devices.
The range advantage of these systems is due to two
factors: first, the transmitter power is higher, up to 100mW.
This is at least twice the power of most wireless
microphone systems. Second, since both the transmitter
and the receiver may have detachable antennas, it is
possible to use a directional antenna on both the
transmitter and the receiver.
In operation, the receiving and transmitting antennas
should be pointed toward each other and oriented
vertically. Elevation for best line of sight will further improve
range. Such a system may be capable of stereo
transmission up to 2500 ft and mono operation up to 3500 ft.
If greater distances are required, it can be accomplished
by using an additional system as "repeater." That is, at the
location of the first receiver a second transmitter is set up to
rebroadcast the signal to a more distant second receiver. Of
course, each of these additional systems has to be on a
different compatible frequency. The practical limit for a
repeater system using standard wireless equipment is about 3
"hops" due to increased noise and distortion.
Summary
It is possible to employ wireless systems for
point-to-point applications in several ways. Both wireless
microphone systems and IEM systems can be used, each
with different adaptations. The modifications are primarily
for AC powering of battery powered devices and for
matching audio signal levels. Special connectors and/or
adapters may also be necessary in some cases.
For moderate distance, single channel applications
may use wireless microphone systems for good results.
Multi-channel, especially stereo, transmission may benefit
from the IEM approach. Longer distance uses will require
directional antennas for wireless microphone receivers or
for IEM transmitters. Maximum range applications can be
handled by the dual directional antenna IEM setup or by
using multiple systems in a repeater configuration.
53
Selection
and Operation
of Wireless Microphone Systems
C HAPTER 5
Application Notes