3
rd
Generation Rack-
Mount RDMS™
44
Quasonix, Inc.
Because the AM back panel BNC output tracks any input signal level changes that are not tracked by the AGC, the
AM output will include any signal amplitude frequency content from (approximately) the inverse of the AGC time
constant up to the AM bandwidth limit. For example, if the AGC time constant is set to 100 ms and the AM
bandwidth is set to 100 Hz, then the AM output will include any AM frequencies between roughly 10 Hz and 100
Hz.
To change the Time Constant value, select Time Constant, then press the Enter key on the front panel. An entry
screen (Figure 59
) prompts the operator to type a new Time Constant, in milliseconds, using the rack’s front panel
numeric keypad. When the new value is entered, press the Enter key on the keypad.
Figure 59: Time Constant Selection and Time Constant Entry Screens
Refer to Appendix B for additional details about recommended AGC/AM settings.
4.4.2.16.4 AGC Freeze
AGC Freeze disables the hardware gain compensation loop such that gain from the RF input to the IF output is
fixed. The receiver front end becomes a constant gain block, which may be useful for making receiver noise figure
measurements or antenna G/T measurements. Note, however, that RSSI measurement and AM/AGC outputs will
continue to reflect changing input levels within a +/-16 dB window around the frozen level. Also, RSSI is calibrated
to be precise enough
—
even varying front-end gain
—
that AGC Freeze is not absolutely necessary to obtain excellent
noise figure or G/T readings via the RSSI measurement.
AGC Freeze can be enabled or disabled through the AGC Menu by pressing Enter when the parameter is selected.
The Enter key acts as a toggle switch.
