Installation Instructions

Hardware Installation
RVP8 User’s Manual
September 2005
2–8
2.2.6 IFD Input A/D Saturation Levels
There are two analog signals that must be supplied to the IFD:
S IF receiver signal
S IF Tx Sample (Burst Pulse) for magnetron, or COHO reference for klystron.
Both of these inputs are on SMA connectors. The IF signal should be driven by the front-end
mixer/LNA/IF-Amp. components, similar to the way that a LOG receiver would normally be
installed. The magnetron burst pulse or klystron COHO reference is also derived in the same
manner as a traditional analog receiver.
Note: Even for fully coherent Klystron and TWT systems, SIGMET
recommends the use of an actual IF Tx sample. If this is not possible, then the
COHO itself may be used instead. If there is phase modulation, then the
phase-shifted COHO should be input.
The A/D input saturation level for both the IF-Input and Burst-Input is +6 dBm (4.5 dBm for
Rev.C or earlier). In almost all installations an external anti-alias filter is installed on both of
these inputs. These filters (if supplied by SIGMET) are mounted externally on one side of the
IFD, and have an insertion loss of approximately 1–2dB. Thus, the input saturation level will be
+8dBm measured at the filter inputs.
For the burst pulse or COHO reference it is important not to exceed the A/D saturation level.
This reference signal should be strong enough so that most of the bits in the A/D converter are
used effectively, but it should also allow a few deciBels below the saturation level for safety.
The recommended power level is in the range –12 to +1 dBm, measured as described in section
D.14. This is important for making a precise phase measurement on each pulse.
In contrast, for the IF receiver input it is permissible (in fact desirable) to occasionally exceed
the A/D input saturation level at the strongest targets. The RVP8 employs a statistical
linearization algorithm to derive correct power levels from targets that are as much as 6dB above
saturation. The actual IF signal level should be established by weak-signal and noise
considerations (see below), rather than by working backwards from the saturation level.