Winter 2008 Issue

Airborne Radio

Radio Control QSYs to 2.4 GHz

By Del Schier, K1UHF

Spektrum 2.4-GHz dual-diversity receiver. Note the tiny dipole wires out of each receiver module.

Almost since the beginning of radio control, hams used 50 MHz for RC and it is still used to this day. However, all good things must come to an end. When I started writing this column, I knew that RC radio manufacturers were about to introduce 2.4-GHz spread-spectrum transmitters and receivers, but flying a RC airplane on 6 meters was still the way to go.

The primary advantage of being both a ham and an RC modeler was that you could fly on 50 MHz. The advantage is there is a much lower chance of a channel conflict than on the unlicensed 72-MHz RC band, and of course, it is a huge concern that you have a clear channel to fly RC aircraft; otherwise there are obvious problems.

In a very short time, 2.4-GHz spread-spectrum (SS) RC radios have become available from most of the major manufacturers and a few new, smaller ones. The use of unchannelized spread spectrum allows many radios to operate at the same flying field with no noticeable interference and or worry about channels.

It is interesting that in 1898 Nikola Tesla actually recognized the advantage of a secure spread-spectrum system for radio control and filed a patent for it. Basically, spread spectrum uses a much wider bandwidth than is needed to transmit the necessary information and relies on a unique synchronized and coded protocol of modulation and frequency hopping, so the receiver only recognizes “its” transmitter. SS has to be synchronized, or married, in order for communication to take place. It is possible that two systems could interfere, but that is very unlikely, as even the simple SS system in a cordless phone would have thousands of unique combinations. The recent availability of inexpensive SS systems for RC model airplanes is probably a direct result of the mass-marketed technology used in cordless phones and WiFi Ethernet.

The features and functions of 2.4-GHz RC equipment are basically the same as VHF equipment, except that the antennas are smaller and easier to deal with. The transmitter can be your older VHF transmitter with a new 2.4-GHz transmitter module plugged in the back, or you can purchase a complete, new dedicated 2.4-GHz SS transmitter.

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