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.
TRANSMIT FUNCTIONAL DESCRIPTION
General
The HF 1 AND HF 2 systems are the same. This example shows the HF 1 system.
When the tune sequence is complete, the HF system goes to the receive/operate mode and is ready to transmit. A PTT discrete starts the operation in the transceiver and antenna coupler.
Transmit Mode
In the receive/operate mode, the PTT discrete from the REU to the transceiver and coupler control logic circuits starts the transmit mode. The coupler control logic circuits energize relays K4 and K5, and de-energize relay K6. This puts a ground on the input to the isolation amplifier. It connects the tuning elements in-line between the discriminator and the antenna.
The coupler control logic sends a ground to disable the off-side coupler. At the same time, it sends a key interlock signal to the HF transceiver. The coupler control logic does this only in these conditions:
There is a ground on the PTT line
There is no disable from the HF 2 antenna coupler
The coupler control logic circuits are not in the home mode
There are no coupler faults.
The control circuits in the transceiver energize relay K1 and tell
the RF circuits to transmit a carrier in these conditions:
There is a ground on the PTT line
There is no transceiver fault
There is a key interlock signal from the coupler.
The RF circuits mix the carrier from the frequency synthesizer
with the mic audio. The RF signal goes through these:
A power amplifier
The relaxed contacts of relay K2
The energized contacts of relay K1
The discriminator in the coupler.
The RF signal then goes through these:
Energized relays K4 and K5
The tuning elements.
The antenna receives the RF from the tuning elements and
transmits it.
Side Tone
When the output from the transceiver power amplifier is more than 40 watts in the AM mode, a switch connects the microphone audio to an audio amplifier. The amplified audio goes to the audio jack and to the flight interphone system for side tone. When the output is less than 40 watts, there is no side tone. When the output is less than 30 watts, an LRU fault occurs.
Key Event Output
The PTT discrete goes to the flight recorder system for key event marking.
OPERATION
General
You use these components to operate the HF radio:
Hand microphone or headset
Radio communication panel
Control wheel mic switch
Remote MIC switch
Audio control panel.
Receive Operation
You use the radio communication panel and the audio control panel to receive transmissions on the HF radio.
On the audio control panel, push the receiver volume control for the HF radio. Turn the control to adjust the volume from the HF radio.
You hear audio on the headset and the flight interphone speakers. To hear sound from the flight interphone speakers, push the speaker (SPKR) volume control to turn on the speaker. Turn the control to adjust the volume of sound from the speaker.
Use the on/off control to turn on the radio communication panel. When you first turn it on, the radio communication panel tunes the VHF radio. Push the HF 1 switch to make the radio communication panel tune the HF radio. A light above the switch comes on to show which radio the panel controls. The frequency displays show HF radio frequencies (2.000 to 29.999 MHz). The HF radio uses the frequency in the active frequency display.
Use the frequency selectors to tune the radio to a new frequency. The standby frequency display shows the new frequency.
When you are sure the frequency is correct, push the frequency transfer switch. The active frequency display shows the new frequency. The HF radio uses the new frequency.
NOTE: When you select a new frequency, the HF coupler drives its tuning elements to the home position.
Listen for audio from the HF radio on the speaker or headset. Adjust the volume control switches on the audio control panel for a comfortable sound level.
Use the HF sensitivity (HF SENS) control on the radio communication panel to adjust the sensitivity of the HF radio receiver.