Microphone and Headphone Jacks

Microphone (mic) and headphone (phone) jacks give

connection points for mic and phone use.

General Description

The VHF antenna receives and transmits RF signals in the VHF frequency range.

The antenna attaches with 10 screws. There is an aerodynamic smoother around the antenna base. This aerodynamic smoother is a sealant. An o-ring seals the coaxial connector. NOTE: For the top antenna, the cable can fall through the hole. Уплотнитель гермет-ки закрывать

When you remove the top antenna, make sure you

attach the cable to something to prevent this.

Receive Operation

The VHF antenna receives RF signals and sends them to the VHF communication transceiver through the coaxial cable. The transceiver sends the RF signal through the receive circuits and then sends the audio to the flight interphone system.

The transceiver also sends data to the selective calling

(SELCAL) decoder.

The VHF 3 transceiver sends data to the aircraft communications addressing and reporting system (ACARS) management unit.

The microprocessor sends the receive frequency to the

frequency synthesizer. The frequency synthesizer sets the

frequency of the AM receiver.

The microprocessor also sends a logic 1 to the transfer switch when the transceiver is in the receive mode. This closes the transfer switch and sends the RF signal from the antenna to the AM receiver.

The AM receiver demodulates the RF input and detects the audio signal. The audio output from the AM receiver goes to these circuits:

• Data output circuits

• Switch S1

• Squelch comparator.

The audio output circuits send the audio signal to the flight interphone system and to the headphone jack.

Do a test of the receive audio circuits with the TEST push button. Push the TEST push button to close switch S1 and send the receive audio to the audio output circuits. This lets the operator hear background noise not normally heard. порог

The squelch comparator circuit compares the detected audio with a threshold value. If the level of the detected audio is larger than the threshold, the squelch circuits sends a ground to switch S1. Switch S1 closes and sends the audio to the audio output circuits.

For the VHF 3 transceiver, the microprocessor changes the audio off signal to a logic 1 when the transceiver is in the data mode. This causes switch S1 to open and disable the audio output and the squelch comparator.

Transmit Operation

The VHF tranceiver receives audio from the remote electronics unit (REU). The transceiver sends the signals through the transmit circuits and then to the antenna for transmission.

During transmission, the microprocessor receives a push-totalk (PTT) signal from the REU. This causes the microprocessor to send a logic 0 to the transfer switch. The transfer switch connects the output of the transmit circuits to the VHF antenna. Mic audio from the REU goes to the transmit circuits in the transceiver. The transmit circuits modulate the RF carrier with the mic audio. This makes an amplitude modulated RF signal. The signal goes to the directional coupler and transfer switch.

The RF signal goes through the transfer switch and to the

antenna. The antenna transmits the RF signal.

The RF output from the directional coupler also goes to the power monitor. The power monitor sends a logic 1 when the output power is larger than 15 watts.

The side tone switch closes when the output power is larger than 15 watts and the transceiver is in the voice mode. The microphone audio goes through the REU to the flight interphone speakers.

For the VHF 3 transceiver, the microprocessor changes the audio off signal to a logic 1 when the transceiver is in the data mode. This sends a logic 0 to the sidetone switch and turns off the sidetone audio.