Overload Indicator; Maximum Input Level - HP 3580A Operating And Service Manual

Model 3580A GENERAL OPERATING INFORMATION
Section III
3-37. Overload Indicator.
3-38. Figure 3-7 is a simplified block diagram showing the
3580A Input Section. The INPUT SENSITIVITY switch
and its associated VERNIER potentiometer control the
input attenuation and gain of the Input Circuits to maintain
the proper signal level at the input of the Mixer. This is an
important function since signals that overdrive the Mixer
can produce harmonic and spurious mixing products which
ultimately appear on the display. The Overload Detector at
the input of the Mixer senses when the signal level exceeds
the design limits and, in turn, lights the front panel
OVERLOAD indicator. As indicated in Paragraph 3-17, the
3580A Input Circuits are well protected and continuous
overloads up to 100 V rms on the
+
30 dB through - 10 dB
ranges or up to 50 V rms on the - 20 dB through - 70 dB
ranges will not damage the instrument. In most cases, an
OVERLOAD indication simply means that the input signal
is overdriving the Mixer and unwanted responses may
appear on the display. Generally, any time the OVER-
LOAD light is off instrument - induced distortion and
spurious is more than 80 dB below the input reference
level.
3-39. Maximum Input Level.
3-40. The maximum input level is the maximum level that
can be applied to the INPUT without overloading the
instrument. The maximum input level is determined only
by the INPUT SENSITIVITY and amplitude VERNIER
settings and is not affected by the AMPLITUDE REF
LEVEL setting. With the amplitude VERNIER control in
the CAL (fully CW) position, the maximum input level is
indicated by a black panel index adjoining the INPUT
SENSITIVITY switch dial and the OVERLOAD indicator
(Figure 3-8). In both Linear and Log modes, the maximum
input level is determined by the black (dB) markings on the
INPUT SENSITIVITY switch dial. These markings repre-
sent either dBV or dBm/600 ohms, depending on the
position of the dBv/LIN - dBm slide switch. When the
amplitude VERNIER control is rotated counterclockwise
\
.......... . . .
INPUT
CIRCUITS
IOOKHz to 150 KHz
FROM VTO
OVERLOAD
DETECTOR
MIXER
IF
SUM 8 DIFFERENCE
FREQUENCIES
Figure 3-7. Input Section.
away from the CAL position, the gain of the input circuit
decreases, the maximum input level increases and the
markings on the INPUT SENSITIVITY switch dial no
longer apply. Table 3-2 lists the maximum input levels for
each INPUT SENSITIVITY setting with the amplitude
VERNIER in the CAL and fully counterclockwise posi-
tions. The maximum levels listed in the table are, in some
cases, considerably lower than the absolute maximum levels
that will produce an OVERLOAD indication. Observing
these maximum levels will ensure optimum performance on
all ranges.
INDEX
Figure 3-8. Maximum Input Index.
Table 3-2. Maximum Input Levels.
POTENTIAL
INPUT SENSITIVITY (VERNIER in CALI (VERNIER fully CCWI DAMAGE LEVEL
SETTIN.G. LINEAR MODE LOG MODE LINEAR MODE
LOG MODE (Continuous Overload)
+ 30d8/20
v
3L6V + 30dBV/dBm 100 V*
+ 40 dBV/dBm 100 V*
+ 20 dB/10 V 10
v
+20 dBV/dBm 20V +30dBV/dBm
~
+ 10 dB/2 V 3.16
v
+ 1CJ dBV/dBm 10
v
+20dBV/dBm
0 dB/1 V 1
v
0 dBV/dBrri 2V ±10dBV/dBm
- 10 dB/0.2 V 0.32
v
- 10 dBV/dBm 1
v
OdBV/dBm 100
v
- 20 dB/0.1 V 0.1
v
- 20dBV/dBm 0.2
v
- 10 dBV/dBm
50V
- 30dB/20 mV 32mV - 30 dBV/dBm 0.1
v
- 20dBV/dBm
!
- 40 dB/10 mV 10 mV - 40 dBV/dBm 20 mV - 30dBV/dBm
- 50dB/2 mV 3.2mV - 50dBV/dBm 10 mV - 40dBV/dBm
- 60dB/1 mV
1 mV
- 60 dBV/dBm
2mV - 50 dBV/dBm
- 70 dB/0.2 mV 0.32 rnV - 70 dBV/dBm
1 mV - 60 dBV/dBm 50
v
*Absolute maximum input voltage.
3-7