Radio Technique

George M. Myers

Radio Technique

Abstract

• The 1988 RC operating environment is reviewed.
• RCMA gold and silver certification labels for transmitters are described and their purpose and significance explained.
• Some manufacturers and RC service shops that can provide certification or modifications are listed.
• The Windbag inflatable-wing aircraft is discussed.

1988 is here—and what do we do about it? As a result of FCC rules which awarded us 50 exclusive RC channels for aircraft and 30 exclusive RC channels for non-aircraft, we face a new situation beginning in 1988. The first change is that all of the old, even-numbered RC channels must be abandoned. These are 72.08, 72.16, 72.24, 72.32, 72.40, 72.96 and 75.64 MHz, which had frequency flags composed of one colored ribbon and one white ribbon.

As a result of AMA decisions related to orderly development of the use of the new channels, RC12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 and 34 are activated to replace the lost channels, and narrow-band transmitters (transmitted signal −55 dB at F0 ±20 kHz) are required for use of the newly activated channels.

Adjacent-channel test matrix

Adjacent-channel transmitters at:

• T +2 (40 kHz above): NBFM X NBAM X OWBAM X
• T +1 (20 kHz above): NBFM X NBAM X OWBAM X
• T (on channel): NBFM X NBAM X OWBAM X
• T −1 (20 kHz below): NBFM X NBAM X OWBAM X
• T −2 (40 kHz below): NBFM X NBAM X OWBAM X

Definitions:

• NBFM = −55 dB at F0 ±20 kHz
• NBAM = −55 dB at F0 ±20 kHz
• OWBAM = −35 dB at F0 ±10 kHz
• X = test condition

Notes on testing:

• NBFM T+2 with T+4: type-checked
• NBFM T+1 with T+2: type-checked

T = channel number of the RC system being tested. Example: T = RC50, so T +2 = RC52, and T +4 = RC54.

A new test matrix is being used by the Myers/Aberle team for testing RC systems. More information is in the column.

These narrow-band transmitters can use any form of modulation (AM, FM, and FM/PCM are the types currently in use). However, old wideband AM transmitters (OWBAM) that have been converted to the new frequencies are still permitted on RC38-56.

The AMA plan does not require that anything be done to existing converted OWBAMs, so we now have to consider OWBAM as well as narrow-band FM (NBFM) and AM (NBAM) as potential sources of interference.

RCMA certification stickers

The members of the Radio Control Manufacturers Association (RCMA), in a move to clearly delineate the performance characteristics of transmitters in use, have begun to affix:

• a gold sticker to transmitters exhibiting narrow-band characteristics (−55 dB at ±20 kHz from F0), and
• a silver sticker to transmitters which more or less meet their original FCC Type Acceptance requirements (−35 dB at ±10 kHz from F0).

Note: Type Acceptance covers more than just bandwidth-offset performance. Practically, both the modulator boards and the RF module determine whether a set meets the spec. It may be necessary (in contests where disputes arise) to label both the transmitter case and the RF module to avoid arguments when a spectrum analyzer is not available.

What you should do (and persuade others to do)

1. Use only narrow-band AM, FM, and FM/PCM transmitters on the low-band channels (RC12 through RC34).
2. Do NOT, under any circumstances, simply crystal-swap an OWBAM set to a new low-band channel. If converted, an OWBAM transmitter MUST have the RCMA gold seal to be sanctioned for use in AMA competition on the low-band channels. A silver seal restricts it to the high-band channels (RC38-56). No seal should bar non-competitive uses, including sport flying.
3. To check that your transmitters are ready for 1988 (and to get Gold or Silver seals, if appropriate), take them to the AMA booth at RC hobby shows (IMAC, Northwest Model Expo, WRAMs, Toledo, Mid-Atlantic Show, RCHTA Show) or to the 1988 AMA Nats. If they need crystal swaps or repairs, send them to a service shop for work.
4. If you suffer interference after completing item 3, and after assuring yourself that others on the flight line have done similarly, spread out. Make use of Owen Black's Pacific Plan, or an equivalent, to set up flight lines and minimize possible interference combinations.

Who is doing narrow-banding and certification

There is good news on the compliance front. Examples of shops and manufacturers offering narrow-banding, crystal swaps, or certification:

• Ace R/C
• Has been shipping narrow-band transmitters since April 1987.
• Will narrow-band/crystal-swap Silver Seven, Olympic, Proline, and old Digital Commander transmitters and affix appropriate stickers for $15. Transmitters must be sent in because both RF boards and the modulator board must be modified—you can't just plug in new RF boards.
• Address: Ace R/C, Inc., 116 W. 19th St., P.O. Box 511E, Higginsville, MO 64037.
• Phone: (816) 584-7121.

• Astronics, Inc.
• Will crystal-swap, return, and certify with a silver sticker your OWBAM transmitter for $25.
• They will also exchange a new 92262 receiver for your old receiver; package price $47.50.
• Address: Astronics, Inc., 11 Autry, Irvine, CA 92718.

• Futaba Corporation of America
• Will narrow-band and crystal-swap OWBAM transmitters, bringing them up to AMA standards, for about $25 (depends on additional repairs) and affix a gold RCMA sticker when appropriate.
• If the transmitter cannot be brought up to narrow-band performance but otherwise meets FCC standards for RC38-56, it gets a silver sticker; otherwise no swap.
• Address: Futaba Corporation of America, 555 West Victoria Street, Compton, CA 90220.

• Polk's Modelcraft Hobbies
• Will accept the transmitter module and receiver from your Aristocraft/High-Tec 420, 620, or 720 system and exchange it with a model 720 module (with RCMA gold sticker) and 720 receiver for $18.95 plus shipping. This change will give you a system capable of the new channels (tested by George Steiner, Bob Aberle, and the author).
• Note: If your transmitter does not have a Channel 1–4 Mix Switch on the top, right-hand corner, you must return the complete transmitter as it needs an update. You can exchange from any channel to any one of the new channels (RC12-34).
• Address: Modelcraft Hobbies, 346 Bergen Ave., Jersey City, NJ 07304. Attn: Exchange Dept.
• Orders phone: 1-800-225-POLK.

Repair stations equipped to narrow-band and certify converted sets:

1. George Steiner (GSP Products)

• 2238 Rogue River Drive, Sacramento, CA 95826.
• Phone: (910) 362-1962.

1. Pete Waters (Kraft Midwest)

• 117 East Main, Upper Level, Northville, MI 48107.
• Phone: (313) 348-0095.

If I hear of other people similarly equipped, I'll pass it on. This is an invitation to send me your name, address, and type of business.

Why narrow-band

When we talk of narrow-banding transmitters, we are really talking about suppressing the power to interfere. Old wideband AM (OWBAM) transmitters have more power to interfere. Eventually, we'll have to get rid of all of them. The plan is to be rid of them by 1991. Why? Because they cause more trouble than they are worth!

Policing the narrow-band channels

So, who is going to make sure that the RC12-34 band is really occupied by narrow-band transmitters, starting in 1988, and that nobody shifts an OWBAM set onto a new RC channel? You are.

If you don't do it, no one else will.

You, the user of RC channels, are expected to police the use of those channels. Unfortunately, no one gives you the authority to force anyone to do the right thing. You have to do it by persuasion. This makes your situation similar to that of the hams among us. Hams have to police the use of ham bands by convincing other hams to use them properly. In the case of a non-ham doing bad things, they may have to call in the FCC.

It's all up to you!

The Windbag

For a change of pace, here's a description of a different kind of aircraft: the Windbag. Modeled after a real airship, the Windbag makes use of an inflatable wing made from rip-stop nylon. Unlike Luther Hus's machines, it has no strings to support the wing. A fiberglass bow shapes the leading edge, and air pressure, combined with the tuck of the cloth, does the rest.

Frank Sailor, of Farmingdale, N.Y., brought this Windbag to me for its first flights. I was totally unprepared for what followed. On the first attempt the plane ran a long way down the runway without showing any interest in flying. On the next attempt I lifted it off with "up elevator" and it departed in a steep climb and a right-hand bank, making like a U-Control model and returning to the ground. Fortunately the videotape proves that I had the presence of mind to shut down the engine halfway through the arc.

We established that we did not have enough control authority to deal with engine torque at full power (Frank had mounted a .61 where the kit called for a .40). We next set up for the control motion possible. The next takeoff was made at part throttle and with full left bank-control input. (Usually one holds right rudder to correct for torque, but this is a pusher and there is no rudder.) After liftoff I reduced power until a left turn appeared, and the flight proceeded with that power setting.

The resulting climb was agonizingly slow, but it was a climb. In level flight at this power setting the controls were quiet but effective. It seemed to fly like a lethargic airplane. Very little "aileron" stick motion was required to produce a turn. I used elevator to hold the nose up in a turn (this is a canard configuration). Later experiments showed that an 11 x 6 propeller turning at 10,000 rpm produced the right flight speed, which I estimate to be about 40 mph.

"Aileron" control tips the whole wing relative to the rest of the machine, and there is a long distance between the center of lift and the center of gravity. Consequently, there is a lot of pendulum effect, and once a steep turn is started you don't have much control authority to stop it. That's when things get interesting. I found it best to add some power, push nose down and opposite roll, and just wait. But it gives your heart a clutch!

The engine was running a little "sick," so I powered down to a landing. That's when I found out that we didn't have enough up-control authority. We learned that you land this thing somewhat like a helicopter: bring it near the ground, then add power, and at the last minute bring up the nose so it can land on the main gear. Crosswind landings are unwise because there is so much wing warp above the wheels.

More experiments followed, with the result that we learned something about deadstick landings. It hangs nose-low in a glide, so you have to dive for the runway in order to have enough control left to lift the nose for landing. The glider has the general characteristics of a parachute descent, with some helicopter autorotation-landing characteristics thrown in for spice.

Not for beginners, but very likely to keep your interest for a while. The Windbag is by Flex-Foil International, B.V., P.O. Box 480-7600 AL, Almelo, The Netherlands. Available from Savon Hobbies, 3622 North 19th Ave., Miami, FL 33142.

Transcribed from original scans by AI. Minor OCR errors may remain.