*
Mixes, filters, and processes the RF signal to make an intermediate frequency (IF) output.
The RTP controls RF sensitivity.
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 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 selected audio goes through an amplifier to these two units:
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HF SYSTEM -HOME/RECEIVE FUNCTIONAL DESCRIPTION
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A phone jack on the transceiver front panel
*
The audio management unit.
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HF SYSTEM -HOME/RECEIVE FUNCTIONAL DESCRIPTION
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HF SYSTEM -TUNE FUNCTIONAL DESCRIPTION
General
The tune sequence begins after the home sequence is complete and the system goes into the standby/receive mode.
The left and right HF systems are the same. This example shows the left system.
Tune Mode Initiation
You select the HF communication frequency on a radio tuning panel (RTP) and key the mic. The PTT signal from the mic starts the tune mode. The same signal goes to the control circuits in the transceiver and the control logic circuits in the antenna coupler.
The coupler control logic circuits energize relays K4 and K5, and de-energize relay K6.
The control logic circuits can start tuning only during these conditions:
*
Ground on the PTT line
*
No disable from the right coupler
*
Coupler control logic circuits are not in the home mode
sequence
*
No coupler faults.
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Tune Mode Operation
The coupler control logic sends a tune-in-progress discrete to the transceiver when the coupler is in tune mode. The logic also latches the PTT discrete to ground until the tuning is complete.
The tune-in-progress discrete energizes relay K2 in the transceiver. The tune-in-progress discrete also goes to the transceiver RF circuits. The RF circuits send an audio tone to the front panel phone jack and to the audio management unit. 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 a carrier in these conditions:
*
The coupler control logic circuits are not in the home mode sequence
*
There is a key interlock signal from the coupler
*
There is a PTT signal
*
There is no transceiver or coupler fault.
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 load to 75 watts.
Because relay K1 energizes in the tune mode, the RF carrier goes to the coupler. The RF carrier goes through the discriminator, relay K4, the tuning elements and relay K5 to the antenna.
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HF SYSTEM -TUNE FUNCTIONAL DESCRIPTION
During tuning, 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 balanced for the selected frequency. When the impedance balances, the control logic circuits remove these signals:
*
Tune-in-progress discrete
*
Ground on the PTT discrete
*
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 in the transceiver and the antenna coupler return to the receive mode. Now the HF system is ready to transmit when it receives a PTT signal.
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