100 RF Circuitry TB9100 Reciter Service Manual
© Tait Electronics Limited January 2006
Fixed Slope
Attenuator, Final
Driver and Fixed
Attenuator
To provide a drive of +20dBm, a silicon-based BJT transistor is used as a
broad band matched Class A final driver. To maintain a fixed input level, a
fixed slope attenuator is introduced at the input to the final driver so that the
attenuation rate (slope) decreases with an increase in frequency. A fixed
attenuator provides a signal level of +11dBm ± 2dB to the input port of the
PA, providing better reverse isolation.
The H band VCO frequency spans from either 400MHz to 440MHz,
440MHz to 480MHz, or 470MHz to 520MHz, according to the product
type.
6.3.5 Exciter Control Circuit
This circuit powers up and shuts down the exciter final driver in a controlled
manner. The exciter needs to power up and shut down in a specified time
sequence during transient and cyclic keying conditions to reduce the
adjacent channel power. The exciter control circuit uses Ex_Key to power
up or shut down the VCO final driver, and PA_Key to power up or shut
down the PA driver.
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