Frequency Coordination; Multi-Channel System Checkout - Lectrosonics SRa5P/E01 Instruction Manual

SRa5P/E01 and SRa/E01 Dual Receivers

Frequency Coordination

IM (intermodulation) is a process of two or more RF
signals mixing in any stage in the transmitter or receiver
that generates another RF signal. If this new signal
happens to land on a carrier, IF or oscillator frequency
you may have interference problems that affect range
or audio quality. The possible combinations also include
odd and even order harmonics of the carriers.
Feel free to contact the factory if you need help in coor-
dinating frequencies. A specialized computer program is
used to perform thousands of calculations and identify
various interfering signals. Potential problems and trou-
ble areas can be identified in advance, and proposed
new frequencies or other solutions can be suggested.
This service is offered to authorized Lectrosonics deal-
ers and other customers who are using Lectrosonics
wireless microphone and wireless IFB systems.
Even with thorough analysis, interference can still be
present from local sources that cannot be predicted in
advance. This makes it mandatory to check out a multi-
channel system before the production or use begins.
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Multi-channel System
Checkout
Interference can result from a wide variety of sources
including TV station signals, other wireless equipment
in use nearby, or from intermodulation within a multi-
channel wireless system itself.
The pre-coordinated frequencies on the chart on the
previous pages address in-system compatibility, but
obviously do not take into account RF signals from
external sources that may be present in the location
where the system will be operating.
Using the scanning process with the RF spectrum
analyzer will identify external RF signals, but it does not
address the compatibility of the selected frequencies.
®
It is always good practice, therefore, to go through the
following steps to make sure the frequencies that are
chosen are compatible within themselves and also free
from external interference.
1. Set up the system for testing. Place antennas in
the position they will be used and connect to the
receivers. Place transmitters about 3 to 5 feet apart,
about 25 to 30 feet from the receiver antennas. If
possible, have all other equipment on the set, stage
or location turned on as well, especially any mixing
or recording equipment that will be used with the
wireless system.
2. Set all receivers on clear channels.
Turn on all receivers, but leave the transmitters off.
Look at the RF level display on each receiver. If
an indication is present, change the frequency to
a clear channel where no signal is indicated. If a
completely clear channel cannot be found, set it for
the one with the lowest RF level indication. Once all
receivers on on clear channels, go to the next step.
3. Turn each transmitter on one at a time. Leave
the other transmitters turned off. Then, as you turn
on each one, look at the matching receiver to verify
a strong RF signal is received. Then, look at the
other receivers and see if one of them is also pick-
ing up the signal. Only the matching receiver should
indicate a signal. Change frequencies on either
system slightly until it will pass this test, then check
again to see that all receivers are still on clear
channels as in Step 2.
4. Turn each transmitter off one at a time. With all
transmitters and receivers turned on, turn each
transmitter off one at a time and look at the RF level
indicator on the matching receiver. It should "fall
silent" and the RF level should disappear or drop to
a very low level. If it does not, change frequency on
that receiver and transmitter and try it again.
IMPORTANT: Any time a frequency is changed on
any of the systems in use, you must start at the
beginning and go through this procedure again for
all systems. With a little practice, you will be able to
do this quickly and save yourself some grief.
LECTROSONICS, INC.