2.4 GHz Radio Control System Tips

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2.4 GHz Radio Control System Tips

Post by Greg Russell-Brown on Mon Nov 21, 2016 8:19 am

Nowadays most aeromodellers use the 2.4GHZ (spread spectrum) radio control systems.

Spread spectrum radios, as the name suggests, are not bound by narrow band frequencies, such as FM (frequency modulation) and PCM (pulse code modulation) which were systems used very widely many years ago.

Instead they spread their radio signals out over a large range of the radio spectrum.

They also use a much higher frequency range 2.4 GHz which is a frequency of 2.4 billion cycles per second, this is well beyond the range of most RF (radio frequency) generated noise that occurs below 300 MHz, making 2.4 GHz much more immune to interference issues.

The main idea behind spread spectrum is to spread the radio transmission out over a wider range of the radio spectrum, thus the name-spread spectrum.

This makes a spread spectrum signal much less likely to run into interference or jamming issues that are common with all narrow band radio transmissions.

Even many spread spectrum radios all transmitting at the same time are very unlikely to interfere with each other as the spread of radio signals are random, changing, or coded.

In most cases any signal conflict happens for such a brief moment, the model never even reacts to it.


2.4GHz Limitations:

As I mentioned earlier, transmitting and receiving in the 2.4GHz high frequency range certainly gets you out of a fair amount of naturally occurring RF (radio frequency) noise that occurs below 300 MHz.

You have probably also noticed that all 2.4GHz devices from cordless phones, WiFi routers, and of course RC spread spectrum radios have very short antennas.

This is because the frequency or wave length is so short, a short antenna is all that is required to transmit and receive 2.4 GHz.

This has made the long unsightly and usually difficult to route RC receiver antenna wire a thing of the past, and has also eliminated the long telescoping antenna that would often get bent on the RC radio transmitter.


So what are the shortcomings?

Blocked and reflected signals.

Unlike the longer wave lengths used in 27-40 MHz RC radios that pass through almost anything, 2.4GHz short wave lengths are easily absorbed or reflected by many objects just like a light wave.

Absorption and reflection of the 2.4GHz signal by parts of the model aircraft could lead to a fail-safe condition if the signal is not strong enough for the receiver to identify it from shielding or reflecting.

This is not so much of an issue with foam, fibreglass or balsa fuselages, but it certainly can be a problem for RC helicopters or multi-rotors that use carbon fibre or aluminium side frames.

Carbon fibre gliders are also a 2.4 GHz challenge.


The Solution:

By mounting several receiver antennas in different locations and orientations within the model (or on the exterior of carbon fibre constructed models), even a couple of inches apart at a 90 degree angle to each other pretty much ensures at least one of these receiver antennas will always pickup a clear and strong signal.

By having two or more receiver antennae placed in different orientations, no matter how the aircraft changes position in the sky, one of the antennas will have enough longitudinal exposure to receive the radio waves from your radio transmitter's antenna.

A transmitter antenna radiates RF out of the sides of the antenna, not out the tip, the same way a receiver antenna receives RF along their length.

This is why you will often see people flying with their 2.4 GHz antenna positioned downwards on the radio.

When the antenna is straight, there is a null zone out the tip where the RF energy is not that strong, so if you fly with the tip of the antenna pointed directly towards the aircraft, you are going to limit your flying range.

Have the antenna pointing towards the ground and more RF energy will reach the aircraft, resulting in a stronger radio link and thus a safer flight with far less chance of running into any radio control range issues.
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Greg Russell-Brown
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