HP 70340A, User Manual

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PWR LIM On Off
Selecting the
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Misc men u and then the
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PWR LIM On Off (A VERA GE PO WER LIMIT
On/O ) function enables or disables the a v erage p o w er limit function.
When
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PWR LIM On Off is enabled, the softkey app ears in in v erse video and the display sho ws
the follo wing:
AVG POWER LIMIT XXX
wher e XXX is the curr ent state of the aver age p ower limit function (either ON or OFF ).
The 4 INSTR PRESET 5 ( 4 I-P 5) state for this function is o.
The A VERA GE PO WER LIMIT On/O function is used to protect a v erage p o w er sensitive
devices during pulse mo dulation.
Note
This function is only a v ailable if option 1E1 (step attenuator) is installed.
Application
The A VERA GE PO WER LIMIT function can b e used during pulse mo dulation to protect
devices sensitive to high a v erage p o w er. When the output p o w er lev el or frequency of the
signal generator is c hanged during pulse mo dulation, the in ternal lev eling algorithm causes the
RF output to b e momen tarily switched to CW to enable the instrumen t's circuitry to sample
the signal lev el and make a correction. If the output of the signal generator is connected to
circuitry that is a v erage p o w er-sensitive, damage to the circuitry could result during this CW
calibration. When in in ternal lev eling mo de, the CW calibration is appro ximately 30 ms.
When the A VERA GE PO WER LIMIT function is o (the preset condition), the CW
calibration will follo w output p o w er lev el and frequency c hanges. The CW calibration will also
o ccur the rst time pulse or logarithmic amplitude mo dulation is enabled. When A VERA GE
PO WER LIMIT is on, the instrumen t's in ternal step attenuator will switch in 90 dB of
attenuation during the CW calibration. This will protect p o w er-sensitiv e circuitry connected
to the RF OUTPUT connector, but will cause extra w ear on the step attenuator. T urning
the function on will also cause a momen tary drop in signal p o w er and, th us, will lengthen
frequency and p o w er lev el switching times to 70 ms.
Pulsed P o w er Pre-Calibration Program
The A VERA GE PO WER LIMIT function causes the in ternal step attenuator to switch in 90
dB of attenuation whenev er frequency or p o w er lev el is c hanged. This causes extra w ear on
the step attenuator.
When y ou kno w the v arious frequencies and p o w er lev els that y ou will b e using in a
test routine, the follo wing program can b e used to gather the CW calibration v alues for
frequency/p o w er lev el pairs. When in sp ecial pulse mo dulation mo de, the calibration v alues
can b e sen t for eac h frequency/p o w er lev el pair and the CW calibration is eliminated. This
program pro vides an alternative to turning the A VERA GE PO WER LIMIT function on and,
therefore, minimizes w ear on the step attenuator.
Signal Generator Menus and Functions 5-89
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