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.