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7
Wireless Solutions for Advancing Communications
Theory of Operation
The M2115RCU radio control unit consists of a radio receiver and a microprocessor-based
decoder/controller assembly. The receiver detects microphone “clicks”—short radio transmissions
when a user presses the push-to-talk (PTT) switch on an external VHF radio. The decoder operates
relays according to the patterns of clicks. The receiver is based on the model M15
receiver/transmitter. Except for the oscillator circuit, the transmitter circuits are not installed; the
oscillator is used to generate a test signal to check operation of the receiver and decoder/controller
assembly.
The receiver is a frequency synthesized dual conversion super heterodyne. It contains two mosfet
dual-gate mixers. The first local oscillator is frequency synthesized and operates at 400 mHz above
the channel frequency. The second local oscillator operates at 455kHz. The filtered output of the
receiver’s diode detector is connected to the input of the decoder/controller board where it is digitized.
The click detection and relay control logic is performed by the embedded microcontroller. The
microcontroller software determines if the signal is a valid radio click. If a valid click is received the
controller opens a window for the configured time interval to allow more clicks to be received. The
controller responds to 3, 5 or 7 pulses within the “window” time and energizes up to three relays. The
relay contacts are connected to the terminal strip on the decoder/controller board for controlling lights
or other external electrical equipment. For protection, relay contact connections from the
decoder/controller to external load circuits may optionally pass through three 5-ampere fuses or
circuit breakers.
The optional antenna lightning protector includes a replaceable gas discharge tube. The AC line
lightning protector also includes an LED which is normally illuminated indicating that the line protector
is operating properly. This LED will remain on even when the unit is turned off.
General System Operation
In order for a pilot to turn on the runway lights, he first sets his radio to the channel frequency used by
the airport radio control unit (M2115RCU). He then briefly presses and releases his push-to-talk
(PTT) microphone switch to produce a sequence of short “clicks”. The first microphone “click” starts
the “window” timer, after which the operator has either 3 or 5 seconds to complete the desired
sequence; either 3, 5 or 7 clicks. On the first click, the microprocessor turns on the “WINDOW” LED,
starts a timer and waits for more pulses. Once the “WINDOW” timer expires, the “WINDOW” LED is
turned off and the received pulse count is reset. During the time the window is open, any additional
clicks are received, and the response of the unit is governed by the selection of the various dip switch
settings. If three pulses are received, the 3-click relay is energized. On the 5th pulse, the 5-click relay
is energized, and on the 7th pulse the 7-click relay is energized. All energized relays remain
energized for the configured timeout period. At the end of this timeout period, all relays deactivate.
