Sabine Wireless: Application and Troubleshooting Guide 2 of 12
1. Dropouts
1.1.
What causes dropouts?
Wireless microphone systems are vulnerable to dropouts,
(momentary loss of audio) and it is often difficult to pinpoint the exact cause of the
problem. Dropouts can be caused by improper antenna positioning, defective antenna
cabling, a problem with the transmitter, a problem with the receiver, a problem with the
sound system. Interference with other RF sources almost never causes dropouts but it
can cause sputtering and ticking in the audio. If you are experiencing dropouts,
consider interference as a last resort. We recommend the following steps to quickly
zero in on the problem.
1.2.
Upgrade your receiver firmware.
The first step is always to be certain that you have
installed the latest versions of the SWM7000 receiver firmware and Remote software.
See the Sabine Remote Software section below.
1.3.
Is the problem with the sound system?
Plug a wired mic into the audio cable
plugged into the back of the receiver. If there are still dropouts, you know the problem
is downstream of your wireless mic. If dropouts stop, you know the problem is with your
wireless mic.
1.4.
Problem with the antennas.
Improper antenna positioning is probably the most
common cause of dropouts. The output power of wireless microphones is limited by
governmental agencies to reduce the chances that transmitters in a neighborhood will
interfere with each other. The downside is that your antennas must be carefully placed
in order to pick up relatively weak signals.
1.4.1.
True Diversity
The SWM7000 system comes with two dipole antennas
(sometimes called “rubber duckies” or “rabbit ears”) that mount on the back of the
receiver. Two SWA700 Front-To-Rear cables are also included so that you can
mount the dipole antennas on the receiver’s rack ears.
Dipole antennas have
a polar pattern of sensitivity that forms a donut
shape
(toroid) with the antenna sticking through the donut hole. The receiver’s reception
is weakest along the axis of its antenna. The transmitter’s antenna also has a
donut-shaped polar pattern with the transmitter sticking through the hole. The
transmitter’s signal strength is weakest if you point the end of mic antenna directly
at the receiver’s antenna.
If there was only one receiver antenna and you held the transmitter in a particular
orientation, the signal strength would drop dramatically possibly causing dropouts.
Another common problem occurs when a signal that propagates directly from the
transmitter to the receiver is mixed with the same signal after it reflects off an object
back to the antenna. Both signals are identical except the reflected signal is slightly
out of phase. Mixing these signals can cause a dramatic drop in signal strength.
This problem is common to all wireless microphone systems.
1.4.2. The SWM7000 receiver overcomes this problem by using a true diversity system
that features
two independent receiver circuits per RF channel
. The receiver
constantly monitors the signal strength from both antennas and automatically
switches to the antenna with the strongest signal.
