Lectrosonics SR Series - Ensuring Multi-Channel System Performance; Frequency Coordination Principles; Multi-channel System Checkout Procedure

SRa5P and SRa Dual Receivers
LECTROSONICS, INC.
22
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.
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.