(5)
The output from the second mixer is filtered by a low-pass (LC) filter and applied to an RF amplifier through an automatic load control (ALC) attenuator. The nominally 100-milliwatt PEP output of the RF amplifier is then applied to the power amplifier. The power amplifier raises the 100-milliwatt PEP input to a nominally 400-watt PEP output that is applied to a low-pass filter. The power amplifier has protective circuits that provide almost instantaneous shutdown of the power amplifiers in the event of excessive power amplifier internal power dissipation.
(6)
Within the low-pass filter, the RF signal is routed through a filter that has been selected by the motor-driven rotary band switches for the operating frequency band. These fixed-tuned, low-pass filters cover the frequency band from 2.0 to 29.999 MHz and remove the harmonics of the output frequency.
(7)
The 400-watt PEP RF output from the low-pass filter is routed through a directional wattmeter and a transmit-receive relay to the external antenna coupler. Forward and reflected power detectors, within the directional wattmeter, provide voltages that are used to generate the ALC signal and to drive the power amplifier protection control circuit. The relay disconnects the receiver from the antenna coupler and connects the transmitter to the antenna coupler. Whenever the transceiver is in the transmit mode, an internal blower provides forced-air cooling to the transmitter circuits to prevent overheating.
5E2
Jun 20/85 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 23-11-02 Page 7
D. Receive Mode
(1)
In the receive mode, the transceiver receives 2.000- to 29.999-MHz USB or AM signals from the external antenna coupler. The receiver uses dual conversion to provide 200-mW received voice audio output during transmit mode.
(2)
The 2.000- to 29.999-MHz signal from the antenna coupler is routed, through the transmit-receive relay in a low-pass filter, to an RF bandpass LC filter in the receiver/exciter. The filter output is applied to a push-pull RF amplifier through an AGC-controlled pin diode RF attenuator. The output from the RF amplifier is then routed through a bilateral up-converter.
(3)
In the first mixer, the 2.000- to 29.999-MHz output from the RF amplifier is mixed with the variable 71.8- to 99.7999-MHz signal from frequency synthesizer. If the received RF signal was a USB signal, the output of the mixer will be the LSB, due to the high side injection into the mixer. Only the 69.8-MHz output of the mixer passes through a 69.8-MHz crystal filter and then into a second mixer. Within the second mixer, the 69.8-MHz signal is mixed with the fixed 69.3-MHz signal from frequency synthesizer. The 500-kHz mixer output then branches to either the SSB or AM IF sections of the receiver.
(4)
In SSB operation, the output of the mixer is applied to the 500-kHz mechanical filter. The output of the filter is amplified by the IF amplifiers and then applied to the product detector. Within the product detector, the signal is combined with a 500-kHz injection signal from the frequency synthesizer. The output of the product detector is the detected audio signal. The audio signal is amplified by an audio amplifier. The output of this amplifier is then switched to the final audio amplifier. The output of the final audio amplifier is the audio output to the audio selecting system. The output of the first audio amplifier is also used to develop the AGC voltage for the IF amplifiers. The IF AGC voltage is also used to develop the RF AGC voltage to control the input RF attenuators.
(5)
In AM operation, the output of the mixer is applied to an AM mechanical filter that is capable of passing both the LSB and USB signals. The 500-kHz output of the filter is amplified by the IF amplifiers and then applied to the AM envelope detector. The audio output of the detector is amplified by an AGC-controlled AM/SELCAL audio amplifier whose output is then switched to the final audio amplifier. The output of the final audio amplifier is applied to the external audio system. If a SELCAL signal has been received, the 0.5-volt audio signal is not switched but is applied directly to the external SELCAL audio system. The output of the first audio amplifier is also used to develop the AGC voltage for the IF amplifiers. The IF AGC voltage is also used to develop the RF AGC voltage to control the input RF attenuators.
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