Radio Technique
George M. Myers
"WHAT new radio should I buy?" More than half of the letters from readers this month have asked the same question. "What RC system can I buy—right now—that will be usable in 1991 and beyond?" One possible answer is: "If you want a general-purpose, airplane-only RC system, then buy a Futaba Conquest PCM system on channel RC12."
Now, why did I pick that particular system and channel? Our tests (Aberle, Myers, and Steiner) have shown it to be a good, low-to-medium-priced system which includes a narrow-band receiver as well as a narrow-band transmitter, and it provides all the usual functions (including servo reversing) plus a good, built-in failsafe. RC12 is usable right now with either wideband or narrow-band equipment. It will continue to be usable with narrow-band systems beyond 1991, assuming that you have either a dual-conversion receiver or a single-conversion receiver with its local oscillator at 71.575 MHz.
"What should I buy?" is a difficult question to answer. I can't guess at your needs. I don't know whether you want to buy the best-performing low-priced system, or the lowest-priced system with "1991 performance." I don't know if you are considering a cheap wideband system, or if you want a narrow-band system with the most impressive assembly of chrome-plated knobs and levers.
Perhaps you want a helicopter radio? A helicopter radio provides all the control functions a beginner needs for sailplanes or powered sport models, and it can also fly a helicopter. A "basic" two-stick 4/5/6-channel airplane system (like the Conquest PCM mentioned a moment ago) isn't suitable for a helicopter, you know.
Should I recommend a system which uses interchangeable crystals, or one that doesn't? Do you need big servos because you intend to fly Quarter Scale? Do you need oversize batteries because you are on your way to LSF level V? There are a lot of factors to consider.
When the choice comes down to an old-design wideband system that you can get at a low price because the dealer is clearing out his inventory versus a new-design, more expensive narrow-band system, you have to think in terms of how much use you will put it to.
An old wideband system will still be acceptable in AMA RC competition (on RC12, 38, 40, 42, 44, 46, 48, 50, 52, 54) until January 1, 1991. Depending on whether or not the FCC chooses to modify Part 95 of its regulations to match the AMA Guidelines, it may or may not be usable as a legal system after 1991.
If it turns out that wideband systems aren't legal after 1991, it may still be possible to replace the receiver with a narrow-band receiver and to retrofit the transmitter with a narrow-band RF module, thereby making it legal after 1991. Either way, you can count on at least four years of useful service. An RC system that has worked hard four years should need extensive service. Four years is a long time. Ni-Cd battery packs average about 100 charges per year. In four years servo wear can easily beat up the servo motors.
Replacing Ni-Cd servos can easily exceed the price of a new system. The closeout buyer should expect to work hard the next few years and shouldn't be particularly worried about losing a plane from some kind of interference. Beyond that, AMA HQ might build a file of radio system acceptances for the FCC. In time, the FCC will be able to tell you whether or not the system you are contemplating has been certificated according to the AMA Guidelines. Right now, they have nothing.
Resource management: Noninterfering RC channel arrangements
I think that Dennis Tienen has the best solution. See "The Whistle Blower, Don't Fly?" page 93 et seq., Model Aviation, March 1987. I urge Dennis to contact me; I'd like to work with him on the system presented in that article and other ideas that will reduce the number of channels used. With the system he described for 1991 as requiring only six channels, as well as the seven old channels and all of the 27 MHz, 50 MHz and 53 MHz bands, much can be done.
Besides that, the FCC could reduce all the wiring to the aviation-model club field down to a plan that would permit four pilots to fly simultaneously using the 60-ft separation. A national assignment plan developed by the AMA or a similar organization would reduce the number of separate channels required.
I think model clubs should establish frequency control boards.
The AMA will hopefully adopt some sort of accepted channel plan. When that happens, the FCC will be able to provide us with definitive guidance.
In closing: I want to urge the AMA to take a strong stand and to push for a national channel assignment plan. Modelers should get involved.
George M. Myers
Flight station plans and the Pacific Plan
Meanwhile, out in California, Owen Black has been working out "The Pacific Plan" for flight stations. It is very clever. The Pacific Plan takes the middle element of each possible 3IM triplet (third-order intermodulation) and puts it on one flight station. Next, the two outside elements are placed on another flight station which must be at least 60 ft. from the flight station containing the middle element. In this way, the two elements that must work together to create 3IM are physically separated by enough distance so that any 3IM they manage to produce is so weak that it can't be detected by an RC receiver.
My Flight Station Game differs from the Pacific Plan in the matter of interlacing assumptions. The Flight Station Game algorithm is based on my assumption that all fliers will eventually stand shoulder-to-shoulder (ignoring the AMA recommendation that a 25-ft spacing be maintained between flight stations). The flight station assignments developed by the Flight Station Game will protect individual fliers from the model-to-modeler interference even when they stand shoulder-to-shoulder.
The Pacific Plan assumes that the required 60-ft separation of flight stations will be maintained. If the fliers move together for some reason, the flight station assignments developed by the Pacific Plan will not protect them from model-to-modeler interference.
The Pacific Plan is arranged so that the channel assignments also avoid 2OP (second-order product), image, and adjacent-channel problems. Owen's schemes are easier to solve if you graph them on a circle because they use exactly one channel (no rejects). Tests by George P. Steiner, using a spectrum analyzer, confirm the validity of Owen's scheme.
The output of the Pacific Plan may seem a little confusing at first, because it permits two operating transmitters at each flight station. In the Flight Station Game, I defined a flight station as a place where only one transmitter operates.
The Flight Station Game (FSGAME)
My Flight Station Game, which was published in the February 1987 issue of Model Aviation, permits you to enter and examine the particular arrangements of RC channels used by your club members. It also provides generalized solutions for 1987, 1988, 1991, and 1995 situations (because they are built into the program in the demonstration). Version 1.0 tried to put equal numbers of RC channels on each flight station—and it contained a bug. I have killed the bug and made other changes. I now offer version 1.3, which tries to maximize the number of channels used. This automatically makes the assignments to flight stations unequal.
If you want version 1.3, it is now available from AMA HQ on 5.25-inch SSDD disks formatted for MS-DOS 2.x or MS-DOS 3.x. Just send a check for $20 payable to the AMA Mortgage Retirement Fund and state your preference. On special order, I can provide single-sided, 48 tpi formats for Access, CCS, Corcomp, IBM, Kaypro, Lobo, Memotech, Radio Shack V/M, Morrow, NEC PC, Omikron, Osborne, Superbrain, Sequa, DEC VT-80, Xerox, and Zenith—ask how we may help you. Note: the program requires the MS-DOS 2.x or 3.x operating system. To order, send check to:
Model Aviation P.O. Box 5065 Tallahassee, FL 32314
If you want to create version 1.3 of FSGAME by modifying your copy of version 1.0, proceed as follows:
Var 13 replaces Ver 10 — replace existing lines
- 250 260
- 250 IF Z$ V OR ZSN THEN 260 ELSE 270
- 260 IF ZSY THEN 1870 ELSE 280
Lines added
- 611 IF YR1987 AND F9 THEN 614
- 612 IF YR1988 AND F12 THEN 614
- 613 IF YR1991 AND F36 THEN 614
- 614 PRINT "NO CAN DO" : PRINT CHR$(171)
- 616 GOTO 600
- 715 IF LT1585 OR L1585 THEN 720 ELSE 740
- 1165 IF LT58S OR LSL585 THEN 1170 ELSE 1190
- 1391 IF JF THEN 1392 ELSE 930
- 1392 FOR J1 TO F : LOOKING FOR STORED ZEROS IN FIRST ROW
- 1393 IF LJI0 THEN 1396
- 1394 PRINT ": NEXT J
- 1395 GOTO 930
- 1396 PRINT TAB(40) "CAN DO" : PRINT CHR$(71) : GOTO 1800
- 1480 GOTO 940
- 1495 IF JF THEN TT1 : GOTO 940
- 1575 PRINT REJ(N1) REJ(NI)
- 1805 IF WSY OR WSN THEN 1810 ELSE 1800
- 1992 IF CTR7 THEN 1994 ELSE 2000
- 1994 PRINT CHR$(131) : CTR0
- 2095 LJI0 NEXT J : CLEANS OUT LJI ARRAY
(End of code replacement instructions.)
Transcribed from original scans by AI. Minor OCR errors may remain.
