Radio Spectrum

Spread-spectrum (S.S.) telecommunications is a signal structuring technique that employs direct sequence, frequency hopping or a hybrid of these, which can be used for multiple access and/or multiple functions. In other words it's a fancy way to modulate a radio frequency wave to transmit data, in this case to control our Model Airplanes. This technology is a major advancement in frequency security (interference reduction) for our radio systems.

Spread Spectrum radio systems for R/C. 2.4 GHZ (Giga Hertz – 2400 million cycles per second of frequency) were approved for use in Canada by Industry Canada on June 23/05 and officially approved for MAAC use on February 18/06.

When you first turn on your Spektrum S.S. radio, it first listens to the band and looks for a clear channel, once it finds one clear channel, it looks for another one. It now takes those 2 channels and transmits its data to the linked receiver. The receiver will only listen to its bound transmitter signal. All receivers come with the transmitter's G.U.I.D. (Globally Unique Identity Code) programmed into the associated receiver. There are over 4.2 billion G.U.I.D. codes that the manufacturers can choose from. If you wish to use your transmitter with another receiver, (question - are receivers and transmitters made by different manufactures interchangeable) all you have to do is to bind the receiver. That is accomplished with a Binding plug and using the Binding button on the back of the transmitter. Each Channel is 1 MHZ wide and 80 channels are available from 2.4 - 2.485 GHZ. Up to 30 systems have been tested at the same time, at the same location and no interference issues occurred. Other manufacturers use frequency hopping with a set frequency of channel hopping under a priority proprietary protocol.

Most of our present radios in the 72 MHZ (Megahertz – or 72,000,000 cycles per second in frequency) band are 20 KHZ apart. We have 50 channels in this band for R/C airplanes. Each channel is 20 KHZ or 20,000 cycles apart.

The advantages of using Spread Spectrum are:
(a) - No fear of someone turning on their radio and shooting you out of the sky,
(b) - 2.4 GHZ is almost impervious to electronic noise from speed controllers, Radio Frequency interference, electrical noise from electric motors, and R.F. noise from CD ignition systems on Gas motors.
(c) - With 2.4 GHZ, servo lead suppression systems are not required,
(d) - Most 2.4 GHZ systems are programmed with fail-safe features on the throttle servo and/or on most of the channels
(e) - The radio transmitter will select the channel or channels you are using

The advantages of the new S.S. system are really evident at some large fun fly events. Rather than thinking in the terms of the traditional frequency impound, think about the concept of a frequency request system. Currently and traditionally you may have a long wait for frequency availability before you could fly with a regular 72 MHZ radio. If you had a S.S. radio, and there was an empty flight station, you simply turned your radio on and go flying.

MAAC Safety code item 4.1, item 8, mandates the use of failsafe parameters if your radio receiver is equipped with fail-safe options. (Throttle must be set to idle in fail-safe).

Help - how does failsafe work?
Failsafe is a preset predetermined set of servo controls in the event radio communication is lost on the plane. The most common is the throttle servo will go to idle when the received radio signal is lost. Some more advanced radios have fail-safe on all channels.

The MAAC safety code rule 4.2, item 3 states that there can be - no more than 5 planes flying at any one time unless operating under rules of a specific discipline.

No frequency control is required for 2.4 GHz spread spectrum radios. For equipment on all other authorized frequencies, members must observe strict frequency control measures. These may include use of a MAAC Frequency Board, Transmitter Impound or other similar system.

Spektrum were the first to market a spread spectrum system for R/C cars and then R/C airplanes. Rapid technological change and new product introduction is a happy fact of life for aero modelers. This article was written in April 2008. The reader must constantly check the advertisements and news releases to stay abreast of changes. At the time of the writing of this article, Spread Spectrum R/C radios were available from JR, Spektrum, Futaba and Airtronics.

Conversion modules for Module Equipped radios are also available.
- Spektrum makes S.S. conversion modules for J.R, Airtronics and Futaba.
- Futaba make conversion modules for only their brand of module equipped radios.
- Extreme power makes modules for Futaba, J.R., Hitec radios, some Airtronic radios, and Multiplex radios

An interesting item: With our 72 MHZ radio systems, the full wavelength of the RF wave is 13.66 feet long. Our antennas for 72 MHZ are 39 inches, exactly a ¼ wave antenna. In 2.4 GHZ, the wavelength is 12.5 centimetres; with most S.S. R/C systems you are capturing the full RF wavelength on 2 or 4 antennas. The advantage here is you are capturing more of the energy of the radio signal.

The major difference here is that the park flyer transmitters transmit a lower level of transmitted RF power. The full range transmits at a higher lever of RF power and therefore can transmit longer distances.