the receiver when tuned across the receive band of frequencies. Since the parametric amplifier is the first
amplifier in the receiver, it determines the noise characteristics for the complete receiver.
2. The power requirements of the parametric amplifier's RF pump are met by an RF module (noise source).
The component in the RF module that generates the pump frequency is a klystron.
3. The low-noise wideband TWT provides additional amplification of the 8-GHz incoming signal.
LEARNING EVENT 30: CONVERTER
The converter unit provides the first frequency conversion for the receiver. The signals applied to the converter
have a bandwidth of approximately 500 MHz. The mixer stage within the converter unit converts the 8-GHz
signals from the TWT to 1,730 MHz. The beacon signal channel can be any designated frequency within the
range from 1,230 to 2,230 MHz which results is an output bandwidth of 1 GHz. The TWT located in this unit
provides the required gain needed to offset the losses incurred in the transmission downline and the rotary joint
appearing between the antenna and the receiver.
LEARNING EVENT 31: AMPLIFIER CONVERTER
The amplifier-converter unit performs two significant functions. The first is that of diplexing between the
beacon and communication channels; the second is that of converting the communication channel frequency to
an output frequency centered at 70 MHz with a bandwidth of 50 MHz.
1. The beacon channel part of the diplexing function is provided with a tunable preselector which can be tuned
within the frequency range of 1,230 to 2,230 MHz, which corresponds to the input operating range of the
tracking receiver. The beacon signal is applied to the tracking receiver.
2. The communication channel part of the diplexing capability is mixed with the local-oscillator injection
voltage to generate the 70-MHz IF. Feedback of the injection voltage into the beacon channel is minimized by
the isolators and the bandpass filters in the unit. The 70-MHz output is amplified by a TWT to the level
required by the communication channel. Two 70-MHz outputs are provided by the amplifier-converter unit;
one output is used as the input to the noise figure meter, and the second is fed through the receiver patch pan to
the bandpass filter.
LEARNING EVENT 32: PRESELECTOR
The preselector section of the receiver consists of the bandpass filter, the 70-MHz IF amplifiers, and the
variable-tuned circuit.
3-25
SS0031
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