Radio Technique

GeorgeMMyers MORE Third-Order Intermodulation 31M avoidance have just received yery nice letter Eldon Wilson AMA 5247 San Angelo TX will share parts now Mr Wilson writes .. wonder messages ever considered Let relate group frequency control July 85 worked . recent West Texas Fun Fly saw 93 transmitters impounded 31 old frequencies new frequencies 29 AM 33 FM transmitters two days flying four six airplanes up time 75640 still being used logged 194 flights single case interference unexplained crash Being origi nals RC since 1950 consider record .. ht stations kept minimum 25 feet apart trans mitters kept minimum 15 feet runway boundary sure have usual industrial transmissions contend paging systems telephone relays within two miles field FAA transmitters 5 miles away dont have TV4 interference caused loose nut stick . Some local fliers claimed site unfit because unex plained interferences gave club group suggestion two months back suggested try Immediately unexplained crashes experienced fliers ceased Only novices continued have interference having learned yet interference caused loose nut stick .. t look map wonder place like San Angelo TX can ever get 93 fliers together just Fun Fly Ive tried years get AMA have meet designed type flier age little kid grandfather its real easy have no competition other spec tators choice prizes won raffle basis chance name put box flight make hold drawing . seventh year just grows grows must high entry fee nothing double year still come back have people 700 miles away attend year average guest drives least 140 miles .. Its quite sight see everything A-scale down Electric flying same time Spectators Choice ballot box contained over 400 ballots two days quick note Texas style like talk lot EW Well thanks podner like style GMM Back July gave universal five-station scheme grouping frequen cies scheme Eldon used Since Ive several calls other groupings four instead five flight lines instance month Ill show make up own groupings spot order fit particular group transmitters number flight stations use contest Sunday flying whatever saw last months test results common worst interference comes Third-Order Intermodulation 3IM Considering 17 frequen cies now use 72 73 MHz band 24 combinations will pro duce 31M call combination trip let because consists three frequen cies mathematically related two times frequency minus fre quency second equals frequen cy third member triplet example 2 x RC40 RC42 cause 2 x 72590MHz 80MHz sub tract 72630MHz get 72550MHz frequency RC38 works same other triplets listed Triplet Table Now want avoid 31M must start knowing flight Channel Assinnment Worksheet FItLn1 FItLn2 FItLn3 FItLn4 ChnI Assign Pro hibited Chat Popu lation Totals lines will have transmit ters will used RC channel frequency Since takes three transmitters make 31M problem fly field ly two flight lines can grab trans mitter go flying right WRONG What about guy pits says Petes up RC38 Joes up RC4O its OK turn RC42 some testing Hell doing some testing right Hell testing Petes receivers ability reject 31M could lead some annoying glitch es learn flight line should keep copy 31M Triplet List handy take care guys want make throttle adjustments control checks etc ground Now have thought firmly mind have decided flight lines want accommodate next step should look popula tion need find out transmitters channel fre quency find large differences numbers like 25 guys RC48 Pur/ Whi should look reason 1985 Nats reason would have operations cement-truck dispatcher Pur/ Whi known publicized prior contest can get 3IM kinds transmitters too know assumption flier should have same number oppor tunities flight should allowed much time other flight flying should finish flight lines simultane ously aim make flight line lists contain same number transmittersor close can get get such distri bution perform procedure given Flight Line/Channel Adjustment Procedure box Lets say following frequency population what face typical contest RclZ1 11C38S RC4OI RC425 RC443 RC46 1C487 RC5O RC5Z RC543 RC562 Drn/Whl Dlu/Whl Red/Whi4 Pur/Whi O Org/Whl 3 Yel/ Whi 1 Total32 Heres suggested format work sheet can used help plan what RC channels use multiple flight lines Theres example use Note Treat known interference being present column Its easylevery flight line population zero 42 Model Aviation Well assume want four flight stations make up worksheet example sketch making four col umns paper Next divide col umns can enter channel number top quarter prohibited channels middle half population bottom quarter less time takes explain have following totals entered Channel Assignment Worksheet FLIFL2FL3 Chul 48 42 Red/whi Asga 56 54 Org/whi FL 4 38 40 44 12 Yel/whi ProhibPur/whiPur/whiPur/whipur/whi ChnI 242 434 ed/whiRed/whiRed/whi Org WhiOrg/whiOrg/whi 38 40 44 5636 2 YeI/whiYeI/whiYeI/whi Popu-7542 tattoo2331 Totals987832 Note population flight line about identical size can hope can now pat ourselves back job well quickly done See easy distribution isnt perfect its probably better single universal arrangement will pro vide particularly small groups like get large groups like Mr Wilsons 93 transmitters probably better off universal arrangement fewer arguments less work point easy make up scheme efficient situ ation Racing pilots time make up heat matrix cards must take care image fre quency problem treating Brn/Whi Whi linked set has put same flight line Yel/ Whi present both others Its possible will set youll have assign set first Ive shown usual situation example Likewise can take care SecondOrder Product interference treating Brn/Whi Blu/Whi Red Whi Pur/Whi Org/Whi linked pairs havent found Second-Order Product much problem left Org/Whi RC54 different flight lines example some things havent shown example Hams fly six meters 54 MHz can mixed 72 MHz channels wherever needed Like wise still some fly 27 Third-Order Intermodulation 3lM RC Channel Triplets Channel Spicing4030120160 kHz RC3B Bm/Whi Whi Brn/Whi Whi Red/Whi Org/Whi RC4O Blu/Whi Witi RC3B Pur/Whi RC42 Red/Whi WhiRC42 RC4O Whi TripletsRC44 RC46 RC3B RC44 RC5O RC4BRC4ORC5ORC4ORCA4RC48 RC48 RC42 RC5O RC44 RC52 RC56RC4O RC48 MHz wouldnt considering kilowatt amplifiers rolling around country trucks really simplify balancing flight lines other hand process can made much complicated Canada us ing virtually 50 interstitial frequencies have about 600 31M triplets check can have same prob lem US 1991 no changes made AMA Phase-Tn Plan existing re ceivers arent im proved method have just explained will work 24 setting up conditions last months tests made observation separating 31M interferers distances five 10 20 feet didnt help reduce 31M true enough its subject misinterpretation Some folks pre Table 4 Field Test Summary Control Transmitter Advantage vs 31M Frequencies Separation Test Receiver AM Single-Conversion RC54 7237 MHz Baseline Distance 206 feet Frequency separations RC Channels Used Test Interferers20 kHz40 kHzBC kHz160kHz RC53 RC52 RC5O RC46 RC52 RC5ORC46 AMAM808588 AMFM 44 43 FMFM 6 1M dOrder Intermodulation Interference repeat last months ooIumnGeore refers again month Control Transmitter Advantage M indicates times farther away its control transmitter receiver can interference source stiii suffer disabiing radio interference 600 triplets other number Theviewed column came back difference will amount ofthe question Does mean no head-scratching involved Perhaps some-amount separation between interone will reduce computerferers regardless distance will help programContinued page 125 Flight Line/Channel Assignment Procedure 1 Take channel tho largest population put Flight Line 1 Put channel number prohibited box other Flight Lines Cross off list channels assigned 2 Take next largest population put Flight Line 2 Put channel number prohibited box other Flight Lines Cross off list channels assigned 3 Examine 31M table Put third members 31M groups FL 1 FL 2 keep populations balanced Put same channel numbers prohibited boxes remaining Flight Lines have yet received channel assignments Cross off list channels assigned 4 Assign channel isnt prohibited Flight Line 3 possible should third largest population Cross off list channels assigned Put channel number prohibited box other flight lines 5 Examine what have now new 31M partners Write FL 1 FL 2 FL 3 etc till run out Flight Lines 6 Pick another population group Find FL isnt prohibited Assign Cross off list channels assigned Add its number prohibited box other flight lines 7 Repeat steps 5 6 until assignments have made February 1986 43 Realize Genuine Improvement RC Flying Geometron Transmitter Support Completely frees hands control sticks levers nothing way Allows Concentrate flying because dont have hold transmitter operating controls Provides full four corner stick mobility Improves accuracy stick movement because transmitter held stable Adjusts two-stick transmitter modifications Simple adjustments arm length shoulder size Transmitter secured safety catch can removed replaced second yet cannot accidentally fall out PURCHASE ALL THREE ITEMS See dealer order direct GEOMETRON CO INC 12 INGLESIDE ROAD LEXINGTON MASSACHUSEITS 02173 617 861-6526 Extremely comfortable use wear Put take off instant hat No bets buckles straps no cord around neck Wearing support transmitter stays place carry plane Doubles ideal ground support offers perfect accessibility keeps transmitter off ground Ruggedly built heat treated aluminum finished heavy duty anodize Assembled stainless steel fasteners Designed constructed extended use695O $99Q PIuo 51 50 ohppng COD 550 adrhhonai cash niorwy order ordy Charges apy6y oSy corsoewS US Mass reoclento add 5% TIMER/STOPWATCH Counts up down preset hold additive feature Time Out sounds alarm auto shutoff Easy read outdoors lithium battery 21 95* PROTECTIVE BAG Made space age aluminum coated nylon Reflects suns heat protects TX dirt andg st special fast acting closure 1 D ONCE YOU USE IT YOU WILL NEVER FLY WITHOUT IT does want fly Ugly Stiks Note nice flaps HA envisioned Saito 45but now becomes Saito 65 bigger Krackeijac 7 lb HA shoots 4 lb does consecutive outsides essentially flatbottom airfoil Enya 46 four-stroke 10-7 prop Thats power stick straight up two-thirds downelevator shocked model mag edi tor commented guys would insist 90 four-strokes such beast HA can pull whatever power needed 65 will have superior vertical perform ance HA says will shorten nose four-strokes heavier HA once awing walker cool hand Youll enjoy comments letter kidded about being speed power happy retorted Taint Bill Thats put 25 Spit Some guys saw fuselage profile said would never get off ground Its rocket am going enjoy luxury flying around easily halfthrottle FS job Au OS 25 going machine ButI yearn able realistic crossed-control slip landing about cabin Surprised learn Krackerjac weighs 7 lb am shooting around 4 lb morning bought Saito 65 Hartsfield says am crazy 45 would ample reminds John Sadler just stubborn Sadler would say Anything OK HA Just way Sinatra patented Bill Winter 4432 Altura Ct FaiPftD4 VA 22030 Radio Technique/Myers Continued page 43 answer No separat ed miles would no 31M Actually spread out trans mitters 40kHz spacing 40 ft 31M effect disappears however transmitters 20kHz spacing have spread out least 80 ft Lets say have decided ig nore 31M deal spreading four flight lines 80-ft intervals Set back 50 ft runway centerMODEL MOTORTM high quality totally glazed ceramic engine mug must modeler Standing 51/2 inches tall large 10 oz capacity its real attention getter definite collectors piece years come OnlyPlus $200 posrage handling per order $6e7 SOs CA residents add sales tax line look landing situation need Control Transmitter Advan tage M 245/50 ust break get 245 adding three 80-ft intervals between first fourth flight lines add five-ft miss-the-pilot distance Add little wet turf land little closer guy far endsay 25 ftand Con trol Transmitter Advantage need jumps 245/25 ultiplied wet-turf effect factor 17 good guess comes out 167 youll look last months Table 6 wont find Ms equal 167 fre quency spacings under 20kHz Receivers will have selective 1991 now Till better pay attention 31M still people favor splitting band AM FM segments would study list 31M trip lets few seconds would see futile idea repeat last months test results Table 4 may see 31M triplet cover band influence almost independent Continued page 128 REPLACEMENT PARTS FOR Kraft Engines Teatori McCoy Talpen 40 RJL ENGINES Call Only Factory Source RJL INDUSTRIES Free Parts Catalog Available RIL Industries ox 5654 dena CA 91107 Phone 818 359-0016 February 1986 125 TRAVEL AIR 2000 52 SPAN 1 SCALE 4CYCLE4O45 SEND $200 FOR COMPLETE CATALOG OF FINE KITS IKON NWST Box 586 Auburn WA 98071 4o 206941-8248 p1 MULTIPLEXThe Competitors Edge ..-J14 Channel ROYAL mc Especially Competition FlyerI Exclusive Flight tested since 1979 2001 FM Narrowband PCM Fast accurate service repair 7725 E Redfield Rd e 105 tsdale Airpark tsdale Arizona 8526 Beemer RC West Distributors Inc 602 483-9577 MEMORY SOFT MODULE features new Fabtronics Mark 3 CDl pointless system Once treat mill system wont settle anything less coupled 4 cycle have Best Two Worlds works equally well 2 cycles twins two cylindars model size engine unit comes pre-drilled disk sensor clamp mounting sensor engine 90 day warranty complete structions conversion timing procedure Unit operates 48 volt low current drain weight mere 2 oz size 2 x 2 x 75 inches Complete system comes ignition coil spark plug on/off switch ignition cable also available seperately Batteries cluded Please state engine size use ordering Converting ignition has ad vantages such tremendous saving fuel less mess no burned-out plugs bet ter idle name few Nearly engine can easily con verted can switch unit plane car boat helicopter another Installation very easy no special tools needed Complete system$6995 Cash MO Certified Check Plus $300 postage handling Personal checks take time clear Illinois residents please add tax Brochure ndable purchase FABTRONICS 375 Isle Royale RdGalesbury 1161401 Radio Technique/Myers Continued page 125 frequency spacing signif icant indication FM transmitters triplet makes inter ference worse So data tells us certain road better 31M situa tion ban FM entirely dont think idea will sell either George M Myers 70 Froehlich Farm Rd Hicksvile NY 11801 1 2 3 Kick/Randolph Continued page 45 bit lean bit rich Most seem arrive too-lean setting ear isnt good Actually exhaust provides best clue proper setting first few times Set needle valve will small amount visible smoke setting will very close correct get exact consistent peak rpm four-stroke engine set needle valve aid tachometer run four-stroke engines lean less 20% oil fuel subject running four-strokers interesting note manufacturer suggests ffipping prop backwards against cpmpression starting case works fact very first four-stroke engine started flipping prop backwards Following instructions started very first flip Traditional starting hand-flipping no problem four-cycle engines ever same starters used two-cycle engines just effective fourstrokers Although have heard back fires kicking props loose larger engines usually result having needle valve set too lean have never experienced problem An extra quarterturn prop nut seems good insurance Propellers Manufacturers usually suggest range propellers engine ideal propeller use best airplane/engine Maxi mum power four-stroke engine produced lower rpm twostroker other factors trans lates needing bigger prop and/or pitch comparablysized two-stroker amount prop thrust put out low-revving engine may amaze performance figures given engine reviewers some magazinesthose show ing peak power output specific prop specific rpmif developed bench runningdont tell whole story practical usage Bench running doesnt show effects props unloading flight best thing feel try flying different props until best suited airplane found key thing remember thrust propel ler gives speed model fly engine simply turns propeller last item difference fourstroke engines crankcase breather pressure tap Since crankcase part carburetion system must vented relieve internal air pressure piston goes up down bit oil drains breather good idea vent outside airplane engine cowled breather vent good place shot oil after flying session give bearings little protection should part clean-up procedure Four-cycle engines stay No doubt will become commonplace two-cycle engines future dont have get Youll love RC Aerobatics/Van Putte Continued page 47 scores Figure M 1A Rolls seems wind direction never right end up doing maneuver crosswind Its tough enough wind direction down runway nearly impossible well crosswind unless youre right top elevator control except few superior pilots rest us hate little advice potential purchasers 128 Model Aviation