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Internal airline communications, for example speaking with mechanics, requesting wheelchair assistance,
speaking with ground crews, etc. happen in the 128.8-132 MHz range.
The 136-136.975 MHz range or “new band” was added to the airband in the 1990s. The most common
use is for Air Traffic Control.
You will sometimes hear loud chirps on your PABM1. They come from the Aircraft Communications
Addressing and Reporting System or ACARS. It is a digital communications system that aircraft use to send
and receive short messages to and from ground stations, commonly at a frequency of 131.550 MHz which
is within the range of the PABM1 and so cannot be filtered. The short "beep" at the beginning of the
message is the preamble of the ACARS message, and the rest of the burst, which sounds like loud radio
static, is the actual data stream of the message. ACARS communications include ATC messages to request
or provide clearances, aeronautical operational control messages, and airline administrative control
messages.
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Using Your PABM1 Passive Air Band Monitor
3.1
Basic Operation
Figure 3 shows a block diagram of the PABM1 Passive Airband Monitor. The headphone’s cable acts as
an antenna to pick up transmissions in the 118 to 137 MHz civilian air traffic control band. This range of
frequencies is selected by a passive filter before being fed to the AM demodulator. Received audio is then
presented to the audio output amplifier. The volume of received audio is controlled via potentiometer.
Figure 3 - Block diagram of the PABM1
