The AIR COM can be operated with all types of microphones used in aircraft. We distinguish two different types of microphones:
- Electret microphones (Also called standard microphones): These microphones have a built-in amplifier that is powered by the AIR COM.
- Dynamic microphones: These microphones are purely passive. A relatively weak signal is amplified in the AIR COM.
Settings in the AIR COM:
- Gain: This value controls the internal gain in the radio. This should be set as low as possible, as this favors noise immunity. A level meter makes it easier to find an optimal value.
- Supply: This activates the supply needed for electret microphones.
Most headsets have such microphones. They are characterized by high signal levels. Such microphones are also sometimes used in gliders (on the gooseneck).
Elektret MICs or also called "Standard Mics" have an amplifier on the microphone. This amplifier is supplied by a voltage impressed in the microphone line (so called Supply Voltage or also BIAS Voltage), which comes from the radio.
The gain in the AIR COM (GAIN value) is usually set to 0 or a very low value (maximum 5) for use. The Supply (SUPPLY) must be turned on to provide power to the amplifier in the microphone.
The signals always arrive strong.
The amplifiers in the MICs need quite a lot of power (about 150mA per mic is not uncommon)
The amplifiers amplify noise and interference as well as the audio. This then arrives in the radio and may be amplified again. The noise immunity of Elektret installations is therefore sometimes lower.
Elektret Mics need to be powered (as described above), some MICs (especially modern headsets) need so much power that one supply (this is largely similar in radios and audio panels) can only power one MIC. As a result, parallel connection is sometimes not possible.
These microphones are often used in gliders (on goosenecks) and in very noisy environments (helicopters, open cockpits). The advantage is the low power consumption. Dynamic microphones have a special passive capsule, and usually no amplifier in the microphone. I.e. the signal is picked up and goes directly over the cable to the radio. Naturally, these are VERY weak signals.
The gain in the AIR COM (GAIN value) is usually set to a slightly higher value (30 or more) for use. The power supply (SUPPLY) must be turned off, otherwise, the diaphragm of the microphone will be blocked by the applied voltage.
Some interference overlaps the useful signal because of the weak signal. In general, however, installations with DYN mics tend to be more resistant to interference.
Power consumption is lower, mainly because the input amplifier in the radio is more efficient most of the time.
You can wire two or more MICs to one input without hesitation. You have to work better with the cabling. Resistors additionally weaken the already weak signal.