Hf functional modes General
The HF communication system uses an antenna coupler to keep a 50 ohm impedance match between the transceiver and the antenna. This impedance match decreases reflected power through the RF output circuit back to the transceiver. The HF communication system uses functional modes to complete the receive, tune, and transmit operation. These are the HF communication system functional modes:
Home --исходный
Receive/standby
Tune
Receive/operate
Transmit.
The HF system controls the modes in sequence. The modes do --послед-ть, очередность
not change until all necessary conditions for the modes occur. --произошли
Home Mode
The home mode starts at power-up or when a new frequency is --при включении
set. The transceiver sends a rechannel pulse to the coupler to
start the home mode. The antenna tuning elements in the
coupler move to the home position. The elements are in a
position for minimum attenuation of incoming signals. ----потери в дБ
It is important that the antenna tuning elements inside the coupler be in the home position before you move the coupler. If you move the coupler before the tuning elements are in the home position, damage to internal parts can occur.
Receive/Standby Mode
The receive/standby mode starts when the antenna tuning elements are in the home position.
In the receive/standby mode, the HF system can receive RF
signals at the set frequency. The system is ready to key for --включиться
tuning at any time when it receives a PTT from the REU.
Tune
The tune occurs in these steps:
Tune A (resonance)
Tune B (load)
Tune C (VSWR).
To start tune mode A, key the transceiver. The transceiver
microprocessor sets the AM mode and the key is latched. The --запирается
transceiver sends reduced RF power to the antenna coupler. A --уменьшенный
1 kHz tone can be heard at the transceiver mic jack or through
the flight interphone system as the tuning occurs.
The antenna coupler tunes in 2 to 4 seconds.
The antenna coupler discriminator circuit operates to set phase differences between the RF voltage and current. The antenna coupler tuning elements are set for zero phase difference.
During tune mode B, tuning elements are set to a total impedance of 50 ohms or less and resonant.
During tune mode C, the tuning elements move so that the RF power load makes a VSWR less than 1.3:1. The reflected power is less than 2 watts RF.
Receive/Operate
The receive/operate mode occurs when tune mode C is complete. The key latch is removed. The tuning RF power from the transceiver is tuned off, and the 1 kHz tone stops. The system is ready for reception or transmission.
Transmit
The pilot keys the microphone to transmit.
The coupler adjusts tuning elements to keep VSWR less than
1.3:1 during modulated transmission. The audio tone through
the flight interphone system does not sound at this time.
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.