Aviation Radio Communications Guide
The world of aviation communications is a jungle of incompatibilities. To avoid having pieces that don't fit together be aware of what is out there:
1. There are different types of headsets, intercoms and radios for:
a) general aviation
2. There are different microphone technologies
b) electret (capacitor)
3. There are two main noise reduction technologies for headsets:
4. There are microphones
a) with noise cancellation
b) without noise cancellation
5. There are stereo and mono earphones
1. Headsets: GA vs. ultalight vs. microlight vs. helicopter
There are different headsets for general aviation planes, ultralights, microlights and helicopters.
The main difference between the types are the plugs (and there are no strong techical reasons for so many different types of them).
Ultralight headsets have one five-contact plug (for earphones and microphone combined).
GA headsets have one 1/4" standard earphone plug and a smaller plug for the microphone and PTT (the PTT contact is only used when the headset has a built-in PTT button).
The ACFC has decided to switch from the ultralight type gear to the general aviation standard.
We encourage all our pilots to buy their own headsets. The first thing you have to make sure when shopping for a headset is: It must have the two plugs compatible for general aviation, as shown in the picture below.
2. Electret vs. dynamic microphone
An electret microphone is a capacitor where one of the two capacitor plates is the membrane that swings with the sound.
The capacity of a capacitor is proportional to the distance between the two plates.
The electric load of a capacitor is the voltage over the two plates multiplied by the capacity.
Thus if a capacitor is loaded and its capacity changes, the voltage over it changes also. This changing voltage is the signal that corresponds to the noise the microphone records.
A dynamic microphone works like a loudspeaker in reverse. The membrane moves a magnet that dips into a coil, where a voltage is induced.
GA headsets have mostly electret microphones. Ultalight headset have often dynamic microphones.
Make sure that the radio and the intercom you use works with your headset microphones
The most common problems with incompatibility are:
a) If you are using two headsets, one with an electret and the other with a dynamic microphone it will not work with many intercoms/radios.
b) Some ultalight intercoms are not compatible with electret microphones.
3. Headsets: Active vs. passive noise reduction
The wrong choice here can be painful because active noise reduction (ANR) headsets are expensive. The problem here is not compatibility. A GA ANR headset will work with any GA equipment. But the noise reduction itself may not work properly in the plane you are flying.
Active noise reduction is a new technology. It reduces the noise that comes to your ears. But it does not reduce the signal (voice, music) you want to hear.
The diagram above shows in a very simplified way how this works. An ANR headset has also one (or several) small microphones in every earphone. These microphones record the noise. Then a circuit phase shifts the noise signal by 180° and adds it to the earphone output. Two identical signals, phase shifted by 180° degrees cancel each other out.
What makes this difficult is the fact that the phase-shifted noise signal should reach the ear at the same moment as the noise itself.
I practice it can be that a top of the line ANR headset won't reduce the noise in certain ultalight types because it was tuned to a turboprop or jet cockpit. ANR also seems to work less in open or semi open cockpits.
There are also cases where an ANR worked fine but when a different engine or propeller was fitted to the plane the noise reduction failed completely.
Passive noise reduction in contrast is simply the way a headset muffles the noise by covering the ear.
Consider these steps when thinking about ANR headsets:
a) Do I really need active noise reduction? Consider that good passive noise reduction headsets also muffle the noise quite well. Especially if your flights are under two hours passive noise reduction alone is normally not a problem.
b) Ask around the club and research the internet. Try to find someone who has used the headset you are thinking about in a similar plane configuration.
4. Headsets: Noise cancelling microphone
Headsets these days have all noice cancelling microphones. They work on a simple principle that is not fraught with the same difficulties as active noise reduction in earphones.
A noise cancelling microphone is in fact two microphones. One is pointing forward the other is pointing towards your lips. The signals from the two are subtracted from one another.
Ambient noise reaches both microphones equally and is therefore cancelled out in the process. Your voice however reaches one microphone much more than the other and is therefore not cancelled.
5. Stereo vs. mono earphones
Many new headsets have stereo earphones. Of course one never needs stereo to fly a plane. The only ever reason to have stereo is for listening to music while flying (some intercoms have a music input).
The problem is that not all intercoms, adaptors and radios are compatible with stereo headsets. Most headsets however can be switched to mono.
If only one side of your headset seems to be working, try switching it to mono. Mono / stereo switches can be found:
- on the headset's cable
- as a switch on one of the two earphones
- as a tunring knob on one of the earphones (combined with the balance control)
An intercom is the circuit that allows communication between several headsets in a plane. Important for ultralight flying is to consider the ambient noise.
Normal aviation intercoms often do not cope with the noise levels of an open cockpit. Use a special high noise intercom if your plane has no windscreen or your head is above the windscreen.