Lectrosonics FM870 - Manual (Page 8)

SYSTEM SETUP
This section includes some basic steps that will ensure trouble-free operation of your FM-AV4 system:
1) Make sure the transmitter battery is good, or better yet, new.
2) Charge up the battery pack in the FM870 fully before you use the system.
3) Extend the antenna fully. Position the FM870 so that the antenna is not touching or within 3 or 4 feet
of large metal surfaces such as air conditioning ducts. It is also good practice to position the unit so
that there is a direct "line of sight" between the transmitter and the FM870 antenna.
A wireless transmitter sends a radio signal out in all directions. This signal will often bounce off nearby
walls, ceilings, etc. and a strong reflection can arrive at the receiver antenna along with the direct
signal. If the direct and reflected signals are out of phase with each other, as depicted in the figure
below, a partial or complete cancellation of the received signal will occur. The result will be a "drop
out." A drop out sounds like either a hum or hiss, or in severe cases, may result in a complete loss
of the sound when the transmitter is positioned in certain locations in the room. Moving the transmitter
even a few inches may change the sound of the hum or hiss, or eliminate it. A dropout situation may
become either better or worse as the crowd fills or leaves the room.
In the event that you do encounter a dropout problem, first try moving the FM870 at least 3 or 4 feet
from where it was. This may alleviate the dropout problem. If dropouts are still a problem, try moving
the FM870 to an entirely different location in the room.
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