George M. Myers
Radio Technique
VARIETY is the key word for this month's column. I've got a bunch of short- and medium-length subjects this time.
Tachometer inquiry
To start off, the March 1987 column on tachometers prompted Dr. James Scheiman (Hampton, VA) to write to Nor-Cal Avionics in California in an attempt to purchase an Accutach II. He got his postcard back labeled "Return to sender," which prompted him to send it to me with his request for a new address. MA's publisher, Carl Wheeler, came up with a telephone number. I called it and got to talk with an answering machine. Shortly afterward, Len Horan called me back to explain that Nor-Cal is now a division of A-B Tech, 5689 Glasgow, Troy, MI 48098.
We had a pleasant conversation, during which Len explained that the Accutach II is continuing in production along with other interesting devices. One gadget that seems useful is an Accutach bracket that permits you to attach an Accutach to a helicopter tail boom. Since the Accutach II has a large display, it permits a pilot to hover his chopper and read the main rotor rpm.
1991-compatible systems
Next, the April column also caught some attention. I gave examples of systems that I knew to be 1991-compatible (both receiver and transmitter are narrow-band) and immediately began receiving letters asking, "Why didn't you mention the brand I favor?"
The column gave examples of:
- A low-priced RC system: Acoms FM
- A medium-priced system: Futaba Conquest PCM
- A high-priced system: Cirrus PCM-9 with ABS receiver
- Two receivers sold separately: Kraft KPR-8FD and Airtronics 92245
The point I was trying to make was that 1991-compatible systems are available at every price range. All you have to do is look.
My list of 1991-compatible systems was neither inclusive nor exclusive. For another example, my 1976 Futaba Contest 7 (AM) transmitter has less energy in sidebands and is a narrower-band than any other AM, FM, or PCM RC transmitter that I have seen tested. You'd better read the end of that last sentence again!
The Futaba's matching metal-cased dual-conversion receiver is about as good as an AM receiver can be.
My 1970 Proline Competition Six (metal-cased AM) receiver is as narrow-band as any other AM receiver, and its third-order intermodulation and AM noise rejection are still superior to any other AM receiver I have seen tested.
You just think that you want a list of recommended equipment—what you really want to know is how to pick the good ones.
Crystal-swap checklist
Since this is the year when you will send any old, even-frequency RC systems "home" for a crystal swap to PC38/40/42/44/46/48/50/52/54/56, it seems like a checklist would be a good idea. The service station can't read your mind (and sometimes has trouble with your handwriting, too). Hoping to be helpful, I offer the following memory-joggers. The "old" frequencies will be illegal to use after December 20, 1987.
Old even frequencies (examples):
- 72.080 — BRN/W
- 72.160 — BLU/W
- 72.240 — RED/W
- 72.320 — PUR/W
- 72.400 — ORG/W
- 75.640 — GRN/W
I'll bet that you didn't realize that most of your transmitters are already narrow-band! The Gold Star transmitter testing done by the AMA at some trade shows has revealed that, although 25% to 35% of transmitters in service aren't narrow-band enough, the other 70% of transmitters are OK. All we need to do is filter out the rejects, then we can add narrow-band receivers to the good transmitters and go flying with greater confidence and less interference.
Unfortunately, having a narrow-band transmitter only solves half of the problem. The receiver must be narrow-banded also, so it will listen only to its control transmitter and no others. In the April issue I mentioned two receivers that could be used as replacements. I expect that others are—or soon will be—available, too.
AMA test lab discussion
Creation of an AMA "Consumer's Test Lab" has been suggested many times at AMA Frequency Committee meetings. I don't think much of the idea. My reason is that RC systems are built in batches, and they vary in quality from batch to batch. Even if the AMA could identify and test a sample from each batch, I don't think that the lab would have enough work to justify paying for a full-time staff.
It has been suggested we could set up the $100,000 worth of equipment needed to establish an AMA test lab by adding another dollar to the yearly fee (hoping it would be a one-time assessment). Are you ready for that? If so, we'll have to find a member who would volunteer to perform the tests whenever testable RC systems become available. (The AMA already has a lawyer on retainer, and would be available to fight off the lawsuits which will inevitably arise from such an operation.) If the AMA goes "self-insured" to get away from insurance premiums, we'll have to make sure that we cover that frequency-lab volunteer adequately.
Consider that the number of RC manufacturers is small. Three companies (Airtronics, Cirrus Hobbies, and Futaba) account for most of the equipment sold today. How often do they bring out a new system? Most of what you see consists of old circuits in new packages. But sometimes a tiny change (like adding or changing a few components on the board) makes important improvements in performance. How do we identify the better package?
Next, consider that advertising usually beats the equipment to your favorite vendor's shop by as much as six months. Either the AMA would have to settle for testing prototypes, or we would have to wait for the production batches, then live with the publishing cycle of this magazine to present test information. It is now March 10, 1987, and I am late typing this column for the June 1987 issue of Model Aviation. You can easily see why AMA phone lines could be tied up with phone calls from prospective purchasers of new RC systems asking questions that couldn't be answered.
The FCC (Federal Communications Commission) gets by with just one part-time employee for its Type Acceptance lab, and they deal with a lot more than RC systems. How do they get so much reliability? The manufacturers do the testing and submit reports. What the man at the FCC does is review the reports to ascertain that correct procedures were followed.
In like fashion, the Radio Control Manufacturers Association (RCMA) is considering the feasibility of setting up its own lab for the industry. I don't think that will happen, though. So why not use a commercial lab? That's being considered. All of the above problems will apply to a commercial lab as well.
Type acceptance data
Another subject: the AMA has a continuing effort to collect type acceptance data from the FCC as soon as a piece of equipment qualifies. It hasn't been a roaring success. We have some old type acceptances, but only the new AC R/C, Inc. Silver Seven data is newer than 1980, so far as I know.
The idea here is that information will be stored at AMA headquarters and made available to contest directors and others for the purpose of identifying narrow-band transmitter designs to people doing contest-oriented transmitter processing. I will print that information as soon as I get it (if I get it).
George M. Myers 70 Froehlich Farm Rd. Hicksville, NY 11801
Transcribed from original scans by AI. Minor OCR errors may remain.
