Lectrosonics SRb_SRb5P User Manual download pdf (Page 21)

UHF Digital Hybrid Wireless

Rio Rancho, NM

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:

• 4to5feetbetweentransmitters

• 20to25feetbetweentransmittersandreceiver

antennas

• Receiverantennasnottouchingoneanother

Ifthedistancesarelessthanthis,IMwillbeexagger-

atedandnotlikelytoberealistic.Ifthedistancesare

greaterthanthis,IMproductsthatcouldoccurduring

actualusethatmaynotshowupinthecheckoutproce-

dure.

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.

ThescanningprocesswillidentifyexternalRFsignals,

butitdoesnotaddressthecompatibilityoftheselected

frequencies.Alwaysgothroughthefollowingstepsto

make sure the frequencies that are chosen are com-

patible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4to5feetapart

andabout20to25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 at a time. 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match-

ingreceivershouldindicateasignal.Changefre-

quencies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transmitterthatisturnedoff.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.

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Lectrosonics SRb_SRb5P User Manual Page 21

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