An item of safety equipment that I have become extremely impressed with, and IMAA promotes extensively, is a Frequency Scanner. This is an electronic goodie, very similar to a transmitter in appearance usually, that is in actuality an R/C receiver with crystals for all the R/C frequencies, and which constantly scans through those frequencies looking for interference or signals. When properly utilized, these scanners will automatically tell you if there is a problem with your radio transmission

Unfortunately, we have to put in capitals, WHEN PROPERLY UTILIZED. I have found that quite a number of people who are supposedly in charge of a scanner have no real idea how it works, or how to utilize to maximum effectiveness. Right now, the scanners that are available to us are pretty primitive, and a firm knowledge of how to use them effectively is necessary.

First off, we must understand just what that scanner is. Basically it is nothing more than a standard R/C receiver that is capable of individually sampling each R/C frequency in rapid order. It is NOT a hypersensitive piece of test equipment that can receive extremely weak signals, and it is always used virtually on the ground, where it is in a very poor location for weak-signal reception anyway.

What this says is that a frequency scanner, as they are now available, will only reliably detect interference that originates on your field. Signals coming from sites other than your field will probably be too weak for the scanner to register, with its simple design and extremely poor reception location.

"Well, Jeez," you say, "If the darned thing won't detect interference, what the heck good is it?" What the scanner does do, and it does it quite well, is to detect interference that originates on your field. The proverbial transmitter left on, some kid playing with his model car in the parking lot, the transmitter that is not well-tuned or is splattering onto adjacent frequencies or is emitting harmonic signals. It has been my experience that these kinds of problems are the source of almost 95% of the interference problems that we as modelers have. More than anything else, the properly utilized scanner will instantly detect the guy in the pits, working on his plane, that turns on "Just for a second to check out my controls", and sends a buddy's plane to its grave. The one act is by far the most common form of interference. The scanner will detect it, and at least give some time for a rapid announcement over a P.A. to get the guy to take off. I have personally seen this one situation save at least three planes. "O.K., now that we understand the limitations of a scanner, how do we use it properly?" you say.

F irst off, as our available scanners are now constructed, they require constant on-hand attention by a scanner operator. There is no way that the scanner is going to do any good if there isn't someone there close by who knows exactly how it works. There are no remote-warning systems available that can give a general warning without monitoring.

The scanner is equipped with a row of LED's each LED representing a specific labeled frequency. The scanner will run through this entire row of frequencies, stopping momentarily at each one in sequence, and sampling that frequency. The LED will light up for the frequency being sampled at that time. If there is no signal on that frequency at that time, the scanner will shift to the next frequency with nothing else happening. If there is a signal on the sampled frequency, (someone is flying on that frequency), an audible, clear tone will be heard on the scanner speaker. The scanner will then move onto the next frequency as per normal.

If there is interference on that frequency, both the normal authorized signal, and the interfering signal will come through on the scanner speaker. This is where the knowledgeable scanner operator is necessary. The normal signal from an operating transmitter will give a clear, even tone when detected. When there are two or more transmissions on the same frequency, the tone will be garbled, irregular tone. The scanner operator must be able to tell an interference signal when the scanner signals it in this way, because the scanner has no automatic notification of interference. This, then, is the normal operation of the scanner.

In my experience, however, the scanner's real value does not lie in detecting interference while a plane is flying, (it is usually too late then anyway), but in detecting a potential problem BEFORE a plane is ever allowed to leave the ground. This is the manner in which we have used the scanner most effectively, and the ashen face of a pilot when we tell him he has a problem before he ever flies is plenty of reward for the expense of a scanner!

When a pilot first comes to the transmitter impound van, the scanner is first checked to see if his frequency is clear. The pilot is then instructed to momentarily turn on his transmitter, and the scanner is rechecked to be sure that it now indicates a transmission on the proper frequency. The indication is that when the LED designating the proper frequency lights up, a clear tone is heard over the scanner speaker at the same time.

If there is no tone when that proper frequency LED lights up, there is a problem! Most usually if this happens, the transmitter is on a different frequency than the pilot thought it was. This is very easy to accomplish; a pilot has several transmitters, and manages somehow to get his frequency flags mixed up, or he has bought a used transmitter that has had its frequency changed, but not the frequency flag/label. Without a scanner, no one would ever know that a problem exists - there are just suddenly a lot of crashes at the field.

When the scanner shows that both the frequency is clear, and that the pilot's transmitter is on the correct frequency, only then is that pilot cleared to fly.

During the transmitter check, the scanner should also be paid close attention to possibly detect a transmitter that is splattering onto other frequencies. On one occasion I personally witnessed, a transmitter was found to be sending out signals on three different frequencies. That pilot was told in no uncertain terms to get his radio checked!!

When a pilot returns his transmitter to the impound after his flight, the scanner is again checked to insure that frequency is indeed clear, showing that the transmitter being returned IS turned off.

By utilizing the scanner in this manner, the most common forms of radio interference are greatly reduced. The scanner is a long way from being a perfect item, it requires close monitoring by a knowledgeable operator, and its ability to detect anything but strong, on-field interference is limited, but it does do a very good job of vastly improving field safety when correctly and completely used.