3
rd
Generation Rack-
Mount RDMS™
145
Quasonix, Inc.
4.5.3.6.5 AGC Time Constant
The Time Constant option, shown in Figure 247, sets the time constant of the AGC back panel BNC output. The
time constant can be set in units of ms (milliseconds). The higher the time constant, the slower the AGC output
voltage will move in response to changes in input signal level.
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.
Figure 247: Antenna Controls Window, AGC Time Constant Selection
4.5.3.6.6 AGC Freeze
The AGC Freeze option 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.
Click on the drop down menu to select On or Off, as shown in Figure 248.
Figure 248: Antenna Controls Window, AGC Freeze Selection
4.5.3.6.7 AGC Zero Mode
The AGC Zero Mode option is shown in Figure 249. The AGC Zero Hold (On/Off) option from the 2
nd
Generation
RDMS was replaced by AGC Zero Mode. There are three available settings, Manual, Hold, or Hold and Save.
•
Manual
–
Means the AGC must be zeroed manually after any frequency or IF bandwidth change, or after a
power cycle
