Manual - 8500A Series Peak Power Meter - Giga-tronics

Series 8500A Peak Power Meters
Internal Triggering
The PPM can generate its own internal trigger from the detected RF video envelope at the detector
output. This triggering mode requires that the power of the RF pulse be greater than the internal trigger
level. The trigger level is an adjustable threshold at which the leading rising edge of a pulse will cause
the PPM to take a reading. The precise time at which a reading is taken following the trigger is
determined by the delay generator. This function of the PPM is called Cursor Delay. See the Cursor
Delay functions in Section 2.8.8.
There are two trigger amplifiers in the PPM, one for the range -20 dBm to -10 dBm and another for the
range -10 dBm to +16 dBm. Selecting trigger levels in the lower range (below -10 dBm) can cause the
trigger to be delayed on the order of 100 ns due to the filtering required to improve trigger stability at
these low levels. The absolute accuracy of the trigger level is about ±1/2 dB near the top of these ranges,
but degrades to about ±2 dBm near the bottom.
Normally, the Trigger Level is set at -10 dBm (default). The internal trigger level can be adjusted by
pressing [MENU] (1) [F1]. A trigger level value between -20 and +16 dBm can then be entered.
If there is no RF pulse present at the detector input or if the pulse amplitude is too low, the PPM will not
internally trigger. When this occurs the display will freeze, the New Data light will not be lit, and the
Ready light will not be on.
If a Model 8502A is being used, the routine will ask whether internal triggering is to be driven by inputs
from channel A or channel B. Press the appropriate Detector Select [A] or [B] key. To select the Internal
Trigger Mode and set the level press:
8501A: [MENU] (1) [F1] [nn.nn] [UNITS]
8502A: [MENU] (1) [F1] [A] (or B) [nn.nn] [UNITS]
(nn.nn = selected trigger level numbers)
Autoscaling changes the internal trigger channel to the displayed channel.
External Triggering
For some test routines it may be desirable to provide an external trigger to the system. This can be
especially useful if the trigger pulse from the external source leads the RF pulse at the detector input by a
small amount of time. Readings can then be taken just prior to the arrival of the RF pulse, allowing close
inspection and measurement of the pulse leading edge.
To use the External Trigger Mode, connect a BNC cable from the TTL sync pulse output of the system
under test (or pulse generator) to the Ext Trigger input on the rear panel of the PPM. To select the
External Trigger Mode, press [MENU] [F2]. Correct operation of the External Trigger Mode can be
verified by noting that the Ready and New Data lights on the front panel are flashing.
☛ NOTE: If you attempt to operate in the External Trigger Mode without supplying the
required trigger as described above, the display will freeze, the Ready light will be on, and
the New Data light will be out.
To select External Trigger, press [MENU] (1) [F2].
2-12 Manual No. 20790, Rev C, November 1998
Superceded by Revision D, March 2009