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Radio Systems how they work

RC Airplane Radio Systems 

"The RC airplane radio system is the heart and brain of radio controlled model airplanes!"

There are many varieties of radios for model airplanes ranging from very simple to very complex. You can probably imagine that the more complex the system is, the more expensive its going to be. There is no point in breaking the bank to get a radio with all the bells and whistles if you don't need them or can't use them with the RC airplanes you plan to fly.

On they other hand, you don't want to buy a radio that you will "outgrow" in a very short time. By the time you finish with this page, you'll be able to make a well-informed choice when shopping for that perfect radio!

What Does a Radio System Consist of?

An RC airplane radio system consists of a transmitter, receiver, servos and batteries. 


Transmitter (Tx): -Hand held controller that sends the pilots inputs to the airplane.
Receiver (Rx): - Electronic unit that rides in the aircraft. Receive signals from the transmitter and relays these signals to the servos. Servos: -Small proportional controlled gear motors that mechanically move the control surfaces on the airplane. Servos are plugged into the receiver where they receives input signals from the pilot.
Batteries: -Both the receiver and the transmitter require a battery pack to operate. The battery packs usually consist NiCd
(Nickel-Cadmium) or NiMH (Nickel-Metal Hydride) batteries.

How Does an R/C Airplane Radio System Work?

The transmitter converts the pilot's movements into a radio signal. The process of converting this signal is called modulation. The transmitter then broadcasts this signal. The receiver inside the airplane picks up this signal the same way the radio in your car picks up the local radio station. The receiver pulls the information from the radio waves and relays this information to each servo. The servo has a servo horn that is attached to its shaft. This horn is attached to a control surface, or engine throttle, via a push rod. When the servo rotates the horn translates the rotation into a linear movement that moves the control surfaces. The movement of the servo is directly proportional to the movement of the control sticks on the transmitter. So the control surfaces on the airplane move exactly the way you move the stick on the transmitter. 

RC Airplane Radio Systems work
How controls are setup

The servos and receiver battery simply plug into the receiver. Most people add a switch between the battery and receiver. The switch allows you to turn the receiver off without removing the battery when you are not flying. A switch with a charging harness allows you to charge the battery without removing it. 

Signal Modulation

The four ways that the transmitter converts the pilots movements into radio signals are:

Amplitude Modulation (AM) - With AM, the radio signal is switched on/off rapidly on a single frequency to the modulate the signal. AM is more prone to interference than frequency modulation.

Frequency Modulation (FM) -With FM, this single switches between two frequencies to modulate the signal. FM is less prone to interference than AM . Standard FM is also referred to as PPM (Pulse Position Modulation).

Pulse Code Modulation (PCM) -PCM is a digital form of FM. The transmitter basically sends the data to the receiver in binary code, which is "0's" and "1's". The standard FM(PPM) transmitter sends the signal to the receiver in a series of pulses.

Spread Spectrum - This is the latest and greatest technology available for RC airplanes. The transmitter checks which frequencies are available and only transmits on frequencies that are not being used by someone else. The transmitter continuously changes the frequency several times a second. 

Which is best for you ? 

There is no doubt that Spread Spectrum is the future of this hobby. Eventually all RC airplane radio systems will be spread spectrum. Although Spread Spectrum is quickly gaining popularity, many people are still using FM radio systems. Radios aren't exactly cheap so most people will keep using the radios they have until they have a need to upgrade.

If money is no object than Spread Spectrum is definitely the way to go. But there is absolutely nothing wrong with getting an FM Radio. The prices are coming down due to the introduction of the spread spectrum systems.

There are some AM systems available for very cheap that will fly your airplane just fine. They are cheap because they are dinosaurs, but they still work! Just keep in mind that the vast majority of RC airplane pilots use either FM or Spread Spectrum. If you decide to go with an FM system you may be wondering whether you should get a standard FM (PPM) or a PCM system. If you are just starting out in the hobby your best bet is to get a standard PPM system. To help you make this decision I recommend that you read Pulse Position Modulation vs. Pulse Code Modulation. You will find that the majority of the people at your flying club will have PPM systems. 

Whether using an AM or FM RC airplane radio system you have to be extremely careful not to transmit on the same frequency as someone else! Two airplanes can not fly on the same frequency at the same time, at least not for very long! Every club has as system for keeping track of which frequencies are in use. Learn how clubs keep track of which RC airplane radio frequencies are being used at any given time. 

Frequency Control
Radio Functions

Each RC airplane radio function requires a channel on the radio. To fly an airplane with rudder control only, with no ailerons you will need at least a "2-channel" RC airplane radio system. A channel each for throttle, elevator and rudder.

To fly an airplane with ailerons you will need at least a "4-channel" RC airplane radio system. A channel for throttle, elevator, rudder, and ailerons. If you plan to stick with the hobby it would make sense to go ahead and buy a "6-channel" radio. This way you won't have to buy a new radio when you get an airplane with flaps or retractable landing gear.

People in different parts of the world use different transmitter modes. Make sure you know the difference between the two transmitter modes. It is important that you get the transmitter mode that your instructor and friends have so they can help you learn to fly. Most RC Airplane radio systems are available for each mode. 

Computer (Programmable) Radios 

While the big question now days is whether or not to get a Spread Spectrum radio system, the big question used to be whether or not to get a “computer” programmable radio. Programmable radios were very expensive compared to the standard radios that most people were used to and perfectly content with. That’s why you will hear a lot of old timers claiming that you don’t need a programmable radio.

There are few things in this world that we need, but there are many things available to make our lives much easier! Programmable radios not only make setting up your airplane a breeze, they also provide an entire range of features that maximize the performance of your airplane while making it easier to fly! Without computer radios, the type of flying that many pilots now enjoy would simply not be possible.

The prices of programmable radios have come down significantly in the past few years. This combined with the fact that computer radios bring the control of RC aircraft to an entire new level has made programmable radios the choice of most pilots.

Servo reversing is about the only feature available on basic 4-channel non-programmable radios. Basic non-programmable 4-channel radios such as the Futaba 4YF are still available. If you have a habit of not sticking with interests very long you may want to consider one of these. However, if you plan to stay with this hobby, a programmable radio makes sence. 

Best Place to buy your radio?

Choosing your first radio can be a daunting task. On the sides of this page you will find eBay listings of some of the most popular beginner radios. I have included a brief explanation of each in order to help you make the right decision based on your situation.

Hopefully you can save some cash by finding a good deal on one of these systems. If you see something you like don't be afraid to bid on it! More often than not, you will find extremely good prices on eBay. 

Controlling RC Frequencies 

"RC frequencies used by toy airplanes are different than the frequencies used by hobby class airplanes."

Toy grade RC airplanes are generally geared towards children and can be found at most department stores. These airplanes operate on RC frequencies of either 27 MHz or 49 MHz. Most toy airplanes can not run on both of these frequencies at the same time. Some toy airplanes operate in a band (narrow portion) of these frequencies allowing more than one toy to operator in a 27 MHz or 49 MHz frequency range.

While there are some pretty neat toy class aircraft available, this web page focuses on hobby grade RC aircraft. Hobby grade RC aircraft have a much wider range of frequencies available so that many enthusiasts can fly their airplanes at the same time while at the local flying field. 

Until the most recent explosion in Spread Spectrum technology, all hobby grade RC aircraft transmitters used RC frequencies in the 72 MHz range. The FCC (Federal Communications Commission) regulates all public airwaves in the United States. The FCC has designated the range of frequencies between (72.010 - 72.990)MHz for radio controlled aircraft. 

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