Radio Technique
George M. Myers
Interference Tests
This morning I received in the mail copies of correspondence between Mr. Geoffrey E. Styles, Director of Public Relations at AMA HQ, and Mr. George M. Wiegman, Secretary of the Lake Shore RC Club (in Illinois). The gist of it is that members of the Lake Shore RC Club cooperated in an attempt to discover the minimum spacing between two RC fields—that is, minimum for their situation.
A test plan was written and tests were executed using standard RC equipment, a CB for communication, and an automobile for distance measurement. The test airplanes orbited the Lake Shore RC Club field at various altitudes from 400 to 1,500 feet (we presume that there are no airfields for man-carrying aircraft nearby), and deliberate attempts were made to interfere, using same-channel transmitters at specified distances. Their log of tests does not indicate whether the RC equipment was all AM, or a mix of AM and FM. In addition, there was no map and no measurements were reported of transmitter output power or frequency accuracy. Therefore, I can't comment on their conclusions, which all relate to their special case, anyway.
I applaud their initiative in planning and executing tests to find data to suit their needs. It would please me to hear that more of my readers do likewise. If so, I next urge that they share their findings with us. After all, the meaning of the word academy is "a place for teaching special skills."
I concur with the Lake Shore RC Club recommendation that "Inter-field interference testing should be conducted, to assure that neither geographical features between RC fields, nor use of various kinds of equipment, will produce interference conditions." Hills can shield you, while power lines can bring interference to you. In the absence of testing, stick to the AMA recommendation of five miles between fields, for safety's sake.
Take note of their comment that "The field CB had difficulty reaching the mobile CB at times, which complicated the test." Based on their experience, you might want to use an intermediate relay station, or stations, to obtain more positive communications. The same power lines, hills, large metal structures (like bridges), long metal fences, variations in antenna alignments, etc., will produce unexpected results with CB just as with RC systems.
The following Lake Shore RC Club members deserve an "Attaboy" from the AMA for their initiative in planning and conducting their tests:
- Bob Bentley
- John Snow, Jr.
- Jon Torgerson
- Deo Cri
- Dennis Bielich
- Jim Leman
- Les Seibert
- Norm George
- John Snow, Sr.
- George Wiegman
- Lynn Stevens
- Rich Woodruff
- Don McCourt
- Roger Hallum
Why bother to test?
You might wonder why I spend so much column space on the subject of interference. Some folks never see the problem. Others can't get away from it. For instance, we hear complaints in club meetings (and in letters and phone calls received from all over the U.S.) of cars and boats running on aircraft frequencies. Cars, in particular, have had an explosion in popularity. Bob Novak (Novak Electronics) told me that 95% of production now goes to cars, and he estimates that 2,000,000 RC cars are now in use!
Hand-in-hand with complaints of misuse of RC channels come complaints about hobby store owners who fail to tell RC-system buyers about the existence of RC Frequency Allocations, which are Federal law (restricting 72 MHz frequencies to Aircraft Only and 75 MHz frequencies to Non-Aircraft Use, except for the shared frequencies 72.160, 72.320, and 72.960, and the Aircraft Only frequency 75.640 MHz). "What can you do about it?" is the cry. ("You" is a collective noun, meaning the AMA.)
In the first place, we must accept the fact that the hobby dealer has neither authority nor the responsibility to control how an RC system is used once it leaves the store. Hobby dealers may spend time explaining the frequency allocations instead of making a sale, but there is no law to compel them to do so if they don't want to.
Next, we should remember that no RCer has any "right" to fly. Flying is a privilege, gained by the goodwill created by a half-century of actions by other model builders (very few of whom flew RC). A little bad feeling generated by one stupid individual can undo thousands of modeler-years of good work. When two people show up at the same place at the same time with RC systems on the same channel and an argument develops as to which has the greater privilege (regarding simultaneous operation of aircraft and non-aircraft on an RC channel designated by the FCC as "Aircraft Only"), the fact that a Federal law pre-exists the dispute will give the aircraft operator a winning edge, but only if the police are summoned and the airplane people can produce an up-to-date copy of FCC Regulation 95, Part E. How many of you can do that?
Calling the police can turn an argument into a feud. Do you need one? Faced with this situation, ask yourself, "What would a prudent man do?" Perhaps all that's necessary is to get some 10¢ copies of the AMA Frequency Plan from AMA HQ and give them to the offenders (in front of witnesses, if possible). If that fails to obtain the compliance you want, you might show the document to the owner of the building, lot, or lake where the transgressions are taking place. Sometimes it makes a difference who you educate.
If Non-Aircraft people are running in a field or pond that's too close to your flying field (and this is where you can do some testing on your own), and if they are using Aircraft Only frequencies, ask them to change crystals. You may have some Purple/White, Blue/White, or Yellow/White crystal sets that they can use in place of their illegal crystals. If so, offer to exchange your crystals for theirs and thereby eliminate the problem. (The frequencies 72.160, 72.320, and 72.960 MHz will continue to be legal for boats and cars till December 20, 1987.)
Crystal-swapping by RC system owners has been legal since November 1984, but crystal-swapping is only legal if the transmitter shows legal emission characteristics after the swap. Very few RC system owners have the equipment and the knowledge to verify emission characteristics, and without that equipment and knowledge, the results of crystal-swapping can be illegal. Ponder that!
When the AMA Frequency Committee set up the Frequency Plan, we corresponded with AMYA, MYRA, ROAR, and other Non-Aircraft organizations, and asked them to teach their members to respect the law. None of them sanction use of Aircraft Only frequencies in their competitions, regardless of whether or not aircraft are likely to be affected. Appeal to those organizations, where applicable, for assistance in resolving your problems. You just might be surprised by all the help you get!
If all else fails, aircraft owners can build some boats or cars and join the fun. You might enjoy it. It is also possible that you will make such a crowd, and win so many races, that the original sinners will go somewhere else. Besides, when you become a voting member of their club, you get the opportunity to introduce any club rules and procedures that you want. Vote your own man into the presidency, and get control of their treasury. One never knows what can be done until one tries!
Do you have any other bright ideas?
Many of the complaints we hear have the common theme, "How do we force the hobby dealers to sell 'Airplane Only' RC systems for airplanes only?" We have covered that thought already, but even if hobby dealers had the authority to regulate use of RC systems, they would be unable to get the job done. Why? Because, as it stands now, the bands aren't purely Aircraft Only and Non-Aircraft Only. Some 72 MHz radios can be used in both Aircraft and Non-Aircraft—legally. The offenders can legitimately claim "confusion."
The situation could improve in 1988, when 72 MHz legally becomes "Aircraft Only" and 75 MHz becomes "Non-Aircraft Only," but it won't unless we change the flag system. Nobody will keep 68+ flag color groups (with multiple duplications) straight in their minds. If we stick with the multicolored flags, we give everybody a built-in excuse for claiming that they are "confused."
The problem would be much simpler if the dealer had only two kinds of flag for sale: red ones stamped "72 MHz for Airplane Use Only" and green ones stamped "75 MHz for Non-Aircraft Use Only"—stamped at the factory.
The logical thing to do is to begin training people to identify their RC channels by number, as was intended from the beginning. Some people don't want to refer to channels by number, but we have a way to deal with that: give them a flag system with only one color for each band. With such a flag, everyone will have to pay attention to the number boards. You can review the Single-Color Flag on page 128 of your 1984–85 rule book.
As I see it, the single-color flag system should be adopted right now as the only flag system and published immediately, to take effect January 1, 1988 and completely replace the present multicolored flag system. I have made that recommendation to the AMA Frequency Committee and Executive Council. If you agree, why not write to your district VP (or to AMA HQ) and say so?
On December 20, 1987, the crossovers in uses between the 72 and 75 MHz groups will disappear, making that time a logical one for a flag change. The sooner we get started making the change at the manufacturer level, the sooner the situation will be improved at every level. Remember, most of the flag trouble we got in 1983 related to the flag system and its late publication (which made it impossible for the manufacturers to have flags on the market at the time when they were needed).
I presume that the existing stocks of ribbons could be used up by attrition (and by 27 and 49 MHz and 6-meter fillers). Normally, a flag gets worn and dirty in two years of use, so if we start with the Single-Color Flag idea right now, the changeover time is right; then we can cut out another problem that is already a nuisance. You now can have two guys trying to fly on the same channel (e.g., RC40) because one of them has the wrong clip (i.e., Black/Yellow for 53.4 instead of Yellow/Black for RC40). It already happens too frequently to be ignored. Why continue to invite mistakes?
George M. Myers 70 Froehlich Farm Rd. Hicksville, NY 11801
Transcribed from original scans by AI. Minor OCR errors may remain.
