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.

Дата добавления: 2015-10-23