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The new FMA Direct FS5 dual-conversion receiver is of the "universal" type, meaning that it can operate from FM RC signals using high- or low-side FM deviation..

On the Hitec Eclipse transmitter you can select the FM deviation for the high or low side by calling up "SFT" (Shift) on the LCD screen. Here you see "SFT.N" where "N" is for negative or low-side FM shift to operate Futaba and Hitec RC receivers. If you select "SFT.P", the "P" is for positive or high-side FM shift to operate Airtronics or JR RC receivers.

Q-21: As I understand it, some RC systems aren’t compatible with others and that it has something to do with "FM deviation." Can you explain this to me?

A-21: The concept is easy and the explanation will sound complicated, but let me try. The compatibility situation you point out occurred when we went to FM RC systems. Today nearly every RC system operates on FM. When designing FM RC equipment, the manufacturer is able to select either high- or low-side FM deviation.

I won’t get into the technical aspects of this, but essentially an RC transmitter operating on high-side FM deviation cannot operate a receiver set for low-side deviation. In other words, a "high transmitter" should operate a "high receiver" and a "low transmitter" should operate a "low receiver." In actual practice, JR and Airtronics FM RC systems operate on the high-side FM deviation, while the Futaba, Hitec, GWS, and FMA Direct systems operate on the low side. Therefore, a JR FM transmitter cannot operate a Futaba receiver. If you stay within your brand of equipment, such as a Futaba transmitter and Futaba receiver, you will not have a problem.

RC transmitters now have six, eight, ten, or more memory positions, so modelers are now buying many extra receivers to work off that one transmitter. If you are buying those "extra receivers," you must make sure you buy the one with the correct deviation that matches your transmitter.

That isn’t the end of the story. Recently RC manufacturers have included a circuit in their transmitters that allows the modeler to select high or low deviation. These transmitters include the Hitec Eclipse and the Polk’s Tracker II (and there are more!). On the receiver side we are also seeing “universal” receivers that are capable of receiving high- or low-deviation signals. An example of this is the new FMA Direct FS5 receiver.

Keep this in mind as you shop for new RC equipment. Remember, if you try to operate two different brands of transmitter and receiver and experience control problems or no control, the first thing you should check is the FM deviation of both components.

—Bob Aberle