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3.4.6 Avg/
P-P
The
AVG/
P-P
(Shift) key toggles between DC average
(
AVG
) power and true AC Peak-to-Peak (
P-P
) power
measurements. The Peak-to-Peak readings are indepen-
dent of DC offsets and signal waveshape within the
bandwidth limits of the amplifier.
When in the
AVG
mode the DC power is displayed. The
front end of the Model 840-C ranges to obtain the best
possible A/D resolution of this signal when in
AUTO
mode. The DC signal displayed is the result of an A/D
conversion using an integration time of 100ms.
When in
P-P
mode, the
P-P
annunciator is lit and the
difference between the highest and lowest measured
powers of the AC signal is displayed. In
AUTO
mode, the
Model 840-C ranges to maximize
P-P
signal while minimiz-
ing amplifier saturation when measuring a small AC signal
in the face of large DC offsets.
3.4.7 REF-dB
The
REF-dB
key serves a dual function, accessed through
either a momentary or a long (approximately 3 seconds)
depression of the key. Both functions compare the
measured power against a reference power before the
result is displayed. Pressing the
REF-dB
key a second
time exits the mode.
A momentary press of the
REF-dB
key (less than 3 sec.)
causes the next power calculation to be temporarily
saved and adopted as a reference power. The meter
then displays ratio or dB calculations against this
adopted reference.
When the
REF-dB
key is depressed for longer than 3 sec.
the Model 840-C recalls the reference power level stored
in long term RAM and uses this recalled value in subse-
quent calculations.
3.4.8 Store Reference
The
STORE REF
key serves a dual function, accessed
through either a momentary or a long (approximately 3
seconds) depression of the key. The function allows
either viewing of the reference power level stored in the
long term RAM or storing of a new reference power level
into that memory location. Pressing the
STORE REF
key a
second time exits this mode.
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