User's Manual

RVP8 User’s Manual
October 2005
TTY Nonvolatile Setups
3–18
processing. Multipliers from 0.0 to +1.0 are generally safe to use because they
shift the trigger into the same pulse period that originally defined it. For
example, a start time of (0.0 msec + (0.98 * PRT)) would position a trigger 98%
of the way up to the next range zero. But, if –0.98 were used, and if the period of
the previous pulse was shorter than the current one, then that shorter period would
become incorrect (longer) as a result of having to fit in the very early trigger.
A small but important detail is built into the algorithm for producing the six user
trigger waveforms. It applies whenever a) the trigger period is internally determined,
i.e., the external pretrigger input is not being used, and b) the overall span of the six
trigger definitions combined does not fit into that period. What happens in this case
is that any waveforms that do not fit will be zeroed (not output) so that the desired
period is preserved. This means that you can define triggers with large positive start
times, and they will pop into existence only when the PRF is low enough to
accommodate them.
For example, if Trigger #2 is defined as a 200.0msec pulse starting at +400.0msec,
then that trigger would be suppressed if the PRF were 2000Hz, but it would be
present at a PRF of 1000Hz. Whenever a trigger does not completely fit within the
overall period it is suppressed entirely. Thus, even though the +400.0msec start time
is still valid at 2000Hz, the entire 200.0msec pulse would not fit, and so the pulse is
eliminated altogether.
Start limits: –5000 to 5000 msec. Width limits: 0 to 5000 msec.
Maximum number of Pulses/Sec: 2000.0
Maximum instantaneous ’PRF’ : 2000.0 (/Sec)
These are the PRF protection limits for this pulsewidth.
The wording of the “Maximum number of Pulses/Sec” question serves as a reminder
that the number shown is not only an upper bound on the PRF, but also a duty cycle
limit when DPRT mode is enabled.
The “Maximum instantaneous ’PRF’” question allows you to configure the maximum
instantaneous rate at which triggers are allowed to occur, i.e., the reciprocal of the
minimum time between any two adjacent triggers. This parameter is included so that
you can limit the maximum DPRT trigger rate individually for each pulsewidth.
Note that the maximum instantaneous PRF can not be set lower than the maximum
number of pulses per second.
PRF limits: 50 to 20000Hz.
External pretrigger delay to range zero: 3.00 usec
Range Zero is time at which the signal from a target at zero range would appear at the
radar receiver outputs. This parameter adjusts the delay from the active edge of the
external trigger to range zero. It is important that this delay be correct when the
RVP8 is operating with an external trigger, since the zero range point is a fixed time
offset from that trigger. When the transmitter is driven from the internal trigger
signals, those signals themselves are adjusted (see Burst Pulse alignment procedures)
to accomplish the alignment of range zero.
Limits: 0.1 to 1000 msec.