RACE Frequencies in Use

Radio Frequency Details

Radio systems for R/C cars can vary greatly in price and capability. There are a number of different systems available and this can be confusing for beginners.

All radios are described by the Modulation Type and the Frequency Band.

The only other variable is Stick or Wheel type. Stick radios use two joysticks to control speed and direction, while Wheel radios use a trigger system for speed and a steering wheel for direction control. Stick radios are most popular in UK and Europe while Wheel Radios are more popular in the USA.

Glossary of Terms

Modulation Type: This is AM or FM or PCM, which describes the method used to send signals between the transmitter and receiver. Modulation means changing - Frequency Modulation is changing the frequency of a wave signal to send a message. If you stand on the beach watching water waves the Frequency is how often the waves arrive and the Amplitude is the height of the waves.

Frequency band:
R/C cars are only allowed to use frequencies, which fall into specific bands. These bands vary in different countries as follows:
27 MHz band USA, Europe and Asia
75 MHz band USA and Asia
40 MHz band Europe

Any given radio set cannot be changed from one band to another and radios cannot be changed from AM to FM or PCM.

The 27 MHz band has 6 primary channels in the USA, but elsewhere there are another 6 “intermediate” channels available.
The 75 MHz band has 30 channels.
The 40 MHz band has 20 channels.

In our club, the 27 MHz band of 6 primary channels is completely saturated, with some frequencies shared by as many as 4 different cars. If you want to avoid problems then buy a radio in the 75 MHz band from the USA, or one in the 40 MHz from Europe. See table above for the frequencies, which are already in use. When you buy a radio, you can usually specify which frequency you would like.

AM Radio:
This is a radio system, which uses modulation of the signal Amplitude to send messages from the transmitter to the receiver. The amplitude is the height of the waves, the signal is sent by varying the height of the waves. This is the cheapest form of radio system, but it is the most susceptible to interference. Great first time system, but not recommended for serious racing.

FM Radio:
This is a radio system, which uses modulation of the signal Frequency to send messages from the transmitter to the receiver. The Frequency is the width of the waves, the signal is sent by varying the width of the waves, which speeds them up or slows them down. This is the most cost effective form of radio system for club type racing. The system is not totally immune from interference, but it is more reliable than AM. Great clubman’s system, ideal for racing here in Egypt.

PCM Radio:
This is the most expensive form of radio system, which is almost completely resistant to interference. The cost is very high and the majority of club racers would not notice any improvement over a good FM system of half the cost!

Crystal:
A small device called a crystal controls the frequency of a radio. The crystal looks like a small metal “chiclet” with two wire legs. The crystal usually has it’s frequency printed on it’s surface and also may have a paper tag attached which again shows the frequency.

Obviously the crystal in the transmitter must have the identical frequency to the one in the receiver. A crystal “set” is a pair of identical crystals, one for the Transmitter (marked TX) and one for the Receiver (marked RX).

You cannot switch the RX and TX crystals and you cannot use two crystals that both say RX or TX.

Since you can’t change the Band of a radio, you cannot replace a 27 MHz crystal with a 75 MHz crystal.

Synthesized Radio:
Some radio systems are now available with a method of changing frequency that does not rely on crystals. A module is either built into the transmitter or can be plugged into it, which can be changed using small “pots” or rotary switches.

Radio transmitters with this system can be changed to any frequency in a given band by turning the pots or switches. These transmitters can be used with regular crystal receivers, but if a synthesized receiver is used, then it can also be changed to match the transmitter by turning the pots or switches. This represents the most versatile system for avoiding frequency conflicts.

Frequency Conflict:
This is the expression used to describe what happens when 2 or more cars that want to race together have the exact same frequency. This can only be resolved by one or more drivers changing the frequency of their cars.

Note: An AM radio on channel 66 of the 75MHz band does have a conflict with an FM radio also running on channel 66! The AM, FM or PCM makes little difference when conflicts occur.

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