I
I
r--1 r--1
n I n I
4 I
t
300 f2 SOURCE
TO IMPEDANCE I
6f2 SOURCE
650 A
I OUTPUT I
I
I n
4 I
G
L---
Figure 2-1. Schematic Diagram of Output Divider Cable
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b. Turn instrument on and, for best results, allow a When using the voltage scales, the attenuator setting
minimum warm-up time of 15 minutes. determines the scale to use and also indicates voltage
at output terminals when a full scale voltmeter indi- I
c. Select desired output frequency by adjusting the cation is obtained with a 600 ohm load. If VTVM in-
Range Switch and FREQUENCY controls. dication is less than full scale, terminal voltage can
be determined from the meter indication with the deci-
d. Connect load to output terminals and adjust for mal point relocated to agree with the full scale value. I
desired output level by setting attenuator switch This voltage, as indicated by the VTVM reading and
and AMPLITUDE controls. the attenuator setting, will be referred to as the "in-
dicated" voltage in the discussions that follow.
Refer to the following paragraphs for specific instruc-
1
tions on setting to a frequency, loading. and use of the
output monitor. 2-2C SPECIAL CONSIDERATION WITH
+10/3,0 ATTENUATOR SETTING
2-2~ SETTING To FREQUENCY
I
When the "R.M.S. VOLTS/DB" switch is rotated full
The frequency of a test signal from the 650A is con-
clockwise (+10/3.0 position), a "straight-through"
trolled by the FREQUENCY dial setting and the setting
connection is made in the attenuator to effectively
of the Frequency Range Switch.
disconnect it from the output system. The actual out-
I
put voltage will be the same as the indicated voltage
The FREQUENCY dial is calibrated from .9 through
as read on the 0 to 3 volt scale. Any value load can
10. This dial reading multiplied by the setting of the
be connected to the output terminals and the VTVM
Frequency Range Switch will give the frequency of the
will indicate actual output voltage.
output signal. I
2-2D CONNECTING A 600 OHM LOAD
2-20 LOADING AND USE OF INTERNAL
VOLTMETER
A resistive load of 600 ohms may be connected directly
The internal vacuum tube voltmeter (VTVM) measures to the instrument output terminals. Under these con-
the input voltage to an output attenuator system. This ditions, the indicated voltage will be the voltage at
output attenuator is the "R.M.S. VOLTS/DB' switch the output terminals.
next to the "600fl" output terminals in the lower right
corner of the front panel. The VTVM has two voltage At higher frequencies, test leads must be short and
scales calibrated 0 to 1.0 and 0 to 3 plus a db scale
the shunting capacitance low. At frequencies above
calibrated -12 to +2 dbm (0 dbm = 1 milliwatt into 600
approximately 2 MC, if the external shunt capacitance
ohms). When using the db scales. the relative output is high, use of the "6fL VOLTAGE X.01" terminals of
signal level is determined in db by algebraically add-
the Output Divider Cable is recommended.
ing the db setting of the attenuator switch to the db
reading of the VTVM.
2-2E OUTPUT DIVIDER CABLE
- .NOTE -
The Output Divider Cable contains two resistors con-
nected in series to provide a load of 600 ohms as shown
Calibration of the VTVM section is based upon
in Figure 2-1. The first resistor (594 ohms) is mount-
a 600 ohm resistive load being connected to the
ed in the connector for the instrument output terminals.
instrument output terminals. The output divi-
The second resistor (6 ohms) is mounted at the output
er cable supplied with instrument contains a
end of the cable. These two resistor values provide
load of this value. Loads of other values are
a 100 to 1 (-40 db) division ratio and a source im-
then connected to either set of terminals on
pedance of 6 ohms at the output end of the cable.
the output divider cable.
-4- |
ACEC
HEWLETT-PACKARD
