Owner's manual

SRa5P and SRa Dual Receivers
LECTROSONICS, INC.
22
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identied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.
Multi-channel System
Checkout
Intermodulation(IM)andcrosstalkincreases as the
distance between transmitters and receiver decreases.
Inordertoconductavalidcheckoutofmulti-channel
compatibilityusingtheprocedureshownhere,itisbest
to adhere to the following guidelines:
• 2to3feetbetweentransmitters
• 15to20feetbetweentransmittersandreceiver
antennas
• Receiverantennasnottouchingoneanother
Ifthedistancesarelessthanthis,IMwillbeexaggerat-
edandlikelybeunrealistic.Ifthedistancesaregreater
thanthis,IMproductscouldoccurduringactualuse
thatdonotshowupinthecheckoutprocedure.
Ifyouknowinadvancethatthetransmitterswillbe
closerthan2to3feetduringtheactualproduction,
placethematthatdistanceinstead.
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inthetables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togothroughthefollowing
stepstomakesurethefrequenciesthatarechosenare
compatiblewithinthemselvesandalsofreefromexter-
nal 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. Turn on all receivers. Leave 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areonclearchannels,gotothenextstep.
3. Start with all transmitters turned off. Then turn
on one transmitter. 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
picking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.Repeatthisprocedure
for each transmitter, one at a time.
4. With all transmitters and receivers turned on,
turn each transmitter OFF one at a time. Look at
the RF level indicator on the receiver that matches
the“off”transmitter.Itshould“fallsilent”andtheRF
levelshoulddisappearordroptoaverylowlevel.If
it does not, change the 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.