USER’S MANUAL__________________________________________________________________
274 _________________________________________________________________ M211322EN-D
0916-101
7.6 Sample Noise Level (SNOISE)
This command is used to estimate the current noise level from the receiver,
so that the noise can be subtracted from subsequent measurements. Data
are sampled for 256 pulses at 256 bins, beginning at a selectable range and
spaced by the range resolution at that pulse width. The internal trigger
generator is temporarily set to a special noise rate (usually much lower than
the operating rate) during the process. It is ultimately the user's
responsibility to insure that no returned power is present within the
approximately 32 km sampling interval. In some cases, it may be
necessary to raise the antenna during the noise measurement to avoid
thermal noise pickup from the ground, or from weather targets.
SNOISE has the option of setting up a new sampling range and trigger
generator rate each time it is called. Two bits in the command word
determine which, if any, of the new values overrides the current values
stored in the RVP900. The power-up sampling range is 250 km (input
value of 250), and the power-up trigger rate is 200 Hz (input value of
30000). These initial values persist until such time as they are altered here.
Both input words must always be supplied after the command, even if the
command calls for ignoring one or both of them. The range is supplied
directly in kilometers up to a maximum of 992 km. The trigger rate,
resulting from a given input, is 6 MHz divided by the input value, that is,
the input value is the trigger period in 0.1667 μsec increments. Keep in
mind that the given rate is bounded against the minimum PRT allowed for
the current radar pulse width.
The SNOISE command bounds the requested starting range of the noise
sampling interval. This is to insure that the noise samples fit within the
specified PRT, and within the range mask hardware RAM. The RVP900
sets an error bit when an improper range is requested.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| | 0 0 1 0 0 | Command
|___________________________________________|___________________|
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 | Output 1
|_______________________________________________________________|
.
.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 | Output 16
|_______________________________________________________________|
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