Semco RC100C-2 - Front Panel AGC Zero and AGC Freeze Selection; AGC Zero Using Front Panel

A2537-002/01 February 2020 4-15 SEMCO Proprietary Information
4.5.3 Front Panel AGC Zero and AGC Freeze Selection
AGC Zero zeroes the AGC voltage level at a user-desired signal level (typically the noise floor), providing
a highly accurate measurement of RF Signal Strength from a known (“relative”) reference point.
Figure 4-22 illustrates the steps for enabling <Ch1> AGC Zero. The operator pushes the TUNER button,
uses the UP (2) and DOWN (8) arrows to scroll to AGC Zero in blue, and then pushes ENTER or SELECT
(5) to highlight the AGC Zero ON/OFF window in bright magenta. Using the UP (2) and DOWN (8) arrows,
the operator selects ON and pushes ENTER or SELECT (5).
Using the horizontal LEFT (4) and RIGHT (6) arrows, the operator selects <Ch2> AGC Zero, and pushes
ENTER or SELECT (5) to highlight the AGC Zero ON/OFF window in bright magenta. Using the UP (2)
and DOWN (8) arrows, the operator selects ON and pushes ENTER or SELECT (5).
Figure 4-22
AGC Zero Using Front Panel
The AGC Freeze feature allows the operator to freeze (hold) the gain of the receiver, and is used to
measure receiver IF output SNR for Antenna G/T measurements. Without AGC Freeze, the receiver would
normally amplify incoming signals, including noise; at different gain levels as determined by the selected
IF filter bandwidth.
Freezing (holding) the receiver gain at a fixed level independent of signal input level allows the operator to
measure signal noise floor levels by measuring the IF output at different noise input levels. The AGC
Freeze mode should not be used for receiver mission support.
Using AGC Freeze for Antenna G/T measurements, the operator measures the antenna gain by pointing
the antenna directly at the sun (“Hot Sky”), then away from the sun (“Cold Sky”) and then measuring the
IF signal power difference (i.e., antenna G/T).
The receiver also has programmable attenuators in the RF Tuner design that ensures front-end protection
as well as provide for a linear and calibrated dynamic range. However, attenuator operation will sometimes
affect the accuracy of antenna G/T measurements at approximately -70 dBm to >-50 dBm noise floor
levels. Accordingly, an Attenuator Disable feature precludes this possibility and ensures accurate G/T
measurements. This feature is only available on the Remote (network) GUI and is further described in
paragraph 4.5.8.
Figure 4-23 shows how to enable AGC Freeze using the front panel displays and keypad.
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