HP 333A Operating And Service Manual page 14

Section I I I
3-23. METER INDICATION.
3-24. The 333A/334A meter is calibrated to indicate
in both dB and volts. It i s interesting to notethat the
METER RANGE markings differ from most ac volt-
meter range markings.
On most
ac
voltmeters (600
ohms) 0
dB corresponds
to
the 1 volt range. This is
not true in the case of the 333A/334A. Since the
instru-
ment
is
primarily
a
distortion analyzer, measurements
are
in
dB (relative measurement) rather than in dBm
(absolute measurement).
Zero dB on the 333A/334A
corresponds to 0.3 volt range rather than the 1 volt
range. This allows a10
dB greater
dynamic range of
distortion measurements.
Model 333AI334A
3-30. 333A/334A WT"H OPTION 01.
3-25. E measurements are to be made in dBm, 10
dB
must be subtracted from the METER RANGE
setting.
Thus 0 dB becomes the -10 dBm range for absolute
power measurements. Zero dBm is equal to 1 milli-
watt dissipatedby any impedance andinthis particular
case is 800 ohms. The +10 DECIBELS marking on the
meter face indicates that when voltmeter measurements
are
being made, the indication (METER RANGE plus
meter indication) is 10
dB greater
than when power
(dBm) measurements
are
being made.
3-26. In short, when distortion and voltage measure-
ments are being made, utilize the instrument METER
RANGE and meter scale as they exist. For absolute
power measurements in dBm, simply subtract 10 dB
from the METER RANGE setting.
3-27. USE OF OUTPUT TERMINALS.
3-28. InVOLTMETERand SET LEVEL functions, the
333A/334A can be used
as a
low distortion, wide-band
amplifier. A portion of the meter input (0.1 V r m s
open
circuit for full scale meter deflection is provided
at the OUTPUT terminals.
3-29. In DISTORTION function, the distortion (0.1 V
r m s open circuit forfull scale deflection) i s provided
at the OUTPUT terminals for monitoring purposes.
NOTE
The INPUT terminal and the
OUTPUT terminal should not be
connected directly together when
making low level measurements.
These terminals
are
isolated from
each other by 1 ohm which reduces
the effects o f common mode voltages.
3-31. Operating procedures for the 333A/334A with
Option01
are
the same a s for the standard instrument.
The onlydifference between the standard and optional
instrument i s that the Option 01 has a special meter
and meter amplifier which i s compensated to respond
to W (volume unit) characteristics.
3-32. MANUAL NULLING.
3-33. Since the frequency and balance controls
are
rather sensitive in the MANUAL mode, the following
i n f o r m a t i o n i s s u p p l i e d to simplify nulling the
333A/334A
in
the MANUAL mode. When nulling
the
333A/334A
in
the MANUAL mode, connect the equip-
ment as shown below and adjust
the
333A/334A
fre-
quency and balance controls for the waveform shown
in step a
below. Additional waveforms
are
provided
to simplify nulling.
No harmonic dietortion. Frequency
and balance adjustment correct.
Frequency and balance control im-
properly adjusted.
Frequency approximately
correct;
balance incorrect.
Balance approximately correct; fre-
quency incorrect.
Second harmonic predominant; fre-
quency and balance adjusted.
Second harmonic predominant; fre-
quency and balance adjusted; phase
changed.
Second harmonic predominant; fre-
quency and balance adjusted; phase
changed.
Third harmonic predominant.
Balance incorrect; meter reading
&
scale.
Frequency incorrect; meter readin(
off
scale.
3 -4