Comtech EF Data KST-2000A, Installation And Operation Manual

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Ku-Band Satellite Transceiver Revision 9
Operation MN/KST2000AB.IOM
3–29
3.11.1 Operation
The AGC function is implemented by using two calibrated RF detectors.
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The first detector monitors the TX input (70 or 140 MHz; amplitude range of
–25 to –45 dBm). The DC voltage from the detector is converted to a digital
word in an A/D converter and read by the main processor.
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The second detector monitors the output signal of the SSPA. This detector is cali-
brated for five frequencies over the output frequency range. Additionally, the
second detector calibration covers output power from the saturation point of the
amplifier down to 30 dB (approximately) below saturation.
The calibration data is stored in a non-volatile memory within each SSPA making all
SSPAs interchangeable without loss of system gain accuracy. The estimate of output
power corresponds to the detector voltage linearly interpolated between nearby frequency
and power steps stored in memory. The main processor reads the estimated output power
from the SSPA and computes an error function as follows:
Gain Error = SSPA Output Power – Input Power – Ga UCA
Where Gain_Max is the maximum specified gain of the entire transceiver (converter unit
plus SSPA) and UCA is the value of the up converter attenuator and is set by:
<add/UCA_xx.x (Appendix B)
The main processor processes this data and generates an analog voltage that adjusts the
up converter attenuator to drive the error function to zero.