Home/receive functional Description

General

During the home mode, the antenna coupler tuning circuits are adjusted for minimum antenuation of the incoming RF signal. This is called the tuning circuit home position. The tuning circuits are adjusted to the home position at the start of every new tune cycle and at power up. The HF communication system can receive audio modulated RF after the tuning circuits are in the home position and the HF system goes to receive/standby mode.

Home Mode

The control panel sends tune and modulation mode (AM or USB) data to the HF transceiver control circuits. When the control panel sends a change in frequency, the transceiver control circuits send a rechannel pulse to the antenna coupler control logic. This causes the coupler to begin the home sequence mode. The home mode also starts at power up.

During the home mode, the coupler control logic has these functions:

· Tells the tuning circuits to go to the home position

· Energizes relay K6

· De-energizes relays K4 and K5.

 

The control logic energizes K6 so that the HF system can receive during home mode. When the tuning elements are in the home position, the HF system goes to the receive/standby mode.

Receive/Standby Mode

During the receive/standby mode, relay K1 in the transceiver and K4 and K5 in the coupler de-energize. Relay K6 energizes. Incoming RF signals go to an isolation amplifier and a discriminator in the coupler. The RF output from the coupler goes to the RF section of the transceiver.

The RF section has these functions:

· Amplifies the RF signal

· Mixes, filters, and processes the RF signal to make an intermediate frequency (IF) output.—ПЧ

 

The AM and the USB circuits in the IF section amplify the IF

signal and detect the audio from the signal.

The AM section sends the audio to the SELCAL decoder and to a solid state switch.

Audio from the USB detector also goes to this switch. The mode select output, from the transceiver control circuits, selects audio from either the AM section or the USB section.

The mode select output audio goes through an amplifier to these two points:

· A phone jack on the transceiver front panel

· The flight interphone system.

 

 

 

 

TUNE FUNCTIONAL DESCRIPTION

General

The HF 1 and HF 2 systems are the same. This example shows the HF 1 system.

Before the HF communication system can transmit, the antenna coupler must be tuned to match the impedance between the transceiver and the antenna. The antenna coupler tune circuits keep the impedance at 50 ohms over the HF frequency range. The tune sequence begins with the first push-to-talk (PTT) after the tune circuits are in the home position, and the HF system is in the receive/standby mode.

Tune Mode Initiation      --включение

Select the HF communication frequency on the control panel and key the mic. The mic sends a PTT signal through the REU to start the tune sequence. The same PTT goes to the control circuits in the transceiver and the control logic circuits in the antenna coupler. The coupler control logic latches the PTT(замыкает,запирает) discrete to ground until the tuning is complete.

The coupler control logic energizes relays K4 and K5, and deenergizes relay K6.

The coupler control logic sends a key interlock signal to the HF transceiver. It also sends a disable (запрещающий) discrete to the off-side    antenna coupler to keep the off-side HF system from transmitting.

The coupler control logic can start tuning only in these

conditions:

 

· There is a ground on the PTT line

· There is no disable from the HF 2 coupler

· The home sequence is complete

· There are no coupler faults.

 

Tune Mode Operation

The coupler control logic sends a tune-in-progress discrete to (идет настройка) the transceiver when the coupler is in tune mode. This tune-in-progress discrete tells the transceiver to send a RF carrier (несущую) tuning signal to the coupler.

The tune-in-progress discrete energizes relay K2 in the transceiver. It also goes to the transceiver RF circuits. The RF circuits send a 1 kHz audio tone to the front panel phone jack and to the flight interphone system. This tone tells the operator that the system is in the tune mode.

The control circuits in the transceiver energize relay K1 and tell the RF circuits to send an RF carrier in these conditions:

· There is a PTT signal

· There is no transceiver fault

· There is a key interlock signal from the coupler.

 

In the tune mode, the RF carrier contains no audio. The carrier goes to relay K2. Because relay K2 energizes in the tune mode, the output goes through the resistor. The resistor reduces the power to 75 watts.

Relay K1 energizes in the tune mode and the RF carrier goes to the coupler. The RF carrier goes through the discriminator, energized relay K4, the tuning elements, and energized relay K5 to the antenna.

During the tune mode, the discriminator samples the RF carrier and sends analog signals to the coupler control logic circuits. The control logic circuits use the signals from the discriminator to generate controls for the tuning circuits. The tune mode continues until the impedance of the transceiver and the antenna are in balance for the frequency the flight crew selects. When the impedance balances, the control logic circuits remove these signals:

· The tune-in-progress discrete sequence

· The ground on the PTT discrete

· The 28v dc key interlock signal.

 

If the tune mode does not end within 15 seconds, the coupler

control logic sends a coupler fault to the transceiver.

Operate Mode (Receive)

When the tune mode ends, the HF system begins the operate (receive) mode. Relays K1 and K2 in the transceiver and K4 and K5 in the antenna coupler de-energize. Relay K6 energizes. The HF system is ready to transmit when it receives a PTT signal.

Key Event Output

The PTT discrete goes to the flight recorder system for key event marking.