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ClearOne’s digital technology supports much larger microphone systems than is possible with analog
technology. It should be noted that marginal antenna designs may work well with smaller systems, but they
can cause hits and dropout as the channel counts go up. On the other hand, a well designed antenna system
delivers excellent performance with both big and small systems.
See Pg. 12 for ClearOne’s Free Antenna Design Service Offer.
ClearOne engineers rely on following these design criteria:
Design Goal: Keep the power level of all the microphones between -40 and -60 dBm all of the time to prevent
hits and dropouts.
Design Rules:
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Rule 1: Equal Distance
(1)
The distance to the most distant transmitter should not be more than double the distance to the closest
transmitter. This ensures that all transmitters have relatively equal signal strength at the receiver’s
antenna. Having some transmitters closer than others adjusts the receiver’s sensitivity to the close
by transmitter’s signal which then desensitizes the receiver to the farther away transmitters, which
exaggerates the relative weakness of the farther away transmitters compared to the nearer ones.
If Intermodulation Distortion (IMD) is present (see the appendix below), the IMD signals may shadow
the assigned frequency of some of the transmitters. This adds to the importance of keeping all of
the transmitters an equal distance to the receiver antenna.
When transmitters are too close to the receiver antennas or they are set at a greater transmitter RF power
setting than needed, this can be a cause of IMD.
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Rule 2: Diversity
(2)
The antennas should be separated so that the ends of the transmitter antenna (the null; see appendix
Pg. 7) cannot be aimed at both antennas at the same time. There are also weak and strong spots in the
reception pattern of the room for each antenna that are evened out by having two antennas in two
physical
positions.
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Rule 3: Line of Sight
All wireless microphones exchange the greatest energy transfer in a direct line-of-sight between the
transmitter antenna and the receiver antenna. All transmitters should be in the line-of-sight of
both antennas. Line-of-sight means the transmitters are not blocked by metal, concrete, or similar
radio opaque objects, and there is minimal signal absorption through people’s bodies. Blocking line-of-
sight to the antennas may not cause immediate drop outs, however the transmitter becomes less
resistant to drop outs caused by the system not conforming to the other design rules.
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Rule 4: Cable Loss
The total antenna cable loss should be less than -15 dB at 900 MHz. This is controlled by using the
recommended cable type for the recommended distance.
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Rule 5: Range Loss
Doubling the distance between a transmitter and an antenna cuts the signal strength by a factor of 4
(inverse square law). Keep the antennas as close to the area where the transmitters will be used
as practical without violating Rule 1.
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Rule 6: Transmitter Power
(5)
Adjust the transmitter power to meet the -40 to -60 dBm reading as seen in the ClearOne Wireless
Graphic User Interface scan function.
ClearOne Extension Antenna Application Guide
