HP 651B - Operation

Model 651B
Section in
SiCTION III
OPERATING INSTRUCTIONS
3-1. INTRODUCTION.
3-2. The Model 651B Test Oscillator generates a
stable sine wave output that is available at output im¬
pedance levels of 600 ohms and 50 ohms. The fre¬
quency of the output is variable from 10 Hz to 10 MHz,
and the output power level can be varied from 10
microvolts to 3.16 volts into 600 or 50 ohm loads.
The amplitude of the output will be indicated on the
output monitor, Ml.
3-3. CONTROLS AND INDICATORS.
3-4. Figure 3-1 identifies and describes the function
of all the front and rear panel controls, connectors,
and indicators on the Model 651B.
3-5. ADJUSTMENT OF MECHANICAL ZERO
3-6. The output monitor is properly zero-set when
the meter pointer rests over the zero mark, and the
651Bis in normaloperatingposition atnormaioperat¬
ing temperature, and is turned off. Zero-set the out¬
put monitor as follows to obtain maximum accuracy
and mechanical stability.
a. Turn 651B on and allow it to operate for at
least 20 minutes, to let the meter movement
reach normal operating temperature.
b. Turn 651B off, and allow 30 seconds for all
capacitors to discharge.
c. Insert pointed object (such as tip of ballpoint
pen) into recess on adjustment wheel, and
rotate wheel until meter pointer is exactly
over zero.
3-7. OPERATION.
3-8. To operate the 65IB Test Oscillator, proceed
as follows:
a. Connectprimary acpower to651B (115or 230
V, 50 Hz to 1000 Hz), and set slide switch S4
to proper position.
b. Turn LINE ON switch to ON position. Indi¬
cator lamp will glow, verifying application
of primary power.
c. Set FREQUENCY RANGE switch and FRE¬
QUENCY dial to desired output frequency.
d. Set OUTPUT ATTENUATOR switch to desired
voltage range.
e. Connect load to oulput connector having an
impedance which matches impedance of load.
f. AdjustAMPLITUDEcontrolsfor desired out¬
put voltage, as indicated on output monitor.
g. T he output monitor. Ml, indicates the rms
value of the output volt^e, and the power
level in dBm for resistive loads of 50 ohms.
The output voltage level is obtained by multi -
plying the monitor sc^ereadingsbyfhe. moni¬
tor scale multiplier'^which appearjs on the
OUTPUT ATTENUATOR switch. U^se the fol¬
lowing equation and the impedance correction
graph of Figure 3-2 to obtain the Model 651B
output power level in dBm, for loads other
than those marked on the output connectors.
output Voltage = X 2
i-j D
Where,
-
Load Resistance (Terminating Re¬
Li
sistance)
R. -
Source Resistance(Output Impedance
&
of Oscillator)
V =
Model 651B Output Monitor Reading
m
Problem: A 600 ohm load is placed on the 50
ohm output connector. The Model 651B out¬
put monitor indicates an output of 0.9 volts,
with the OUTPUT ATTENUATOR set on the
1.0 volt (+10 dBm) rar^e. Find the actual
output voltage andpower level (in dBm) of the
Model 65IB.
Solution: The actual output voltage is calcu¬
lated as follows:
Output Voltage = 50 X 2 (0, 9) = 1. 66 V
The indicatedpower level for an actual output
voltage of 1.66 volts would be +17.3 dBm on
the 3.0 V (+20 dBm) range. The actual power
level (with the 600 f^load) is the algebraic sum
of the theoretically indicatedpower level(+17.3
dBm) and a correction factor obtained from
the impedance graph of Figure 3-2. For this
example, a correction factor of -10.8 dBm is
obtained from the 50 output impedance line
of the graph with a 600 load. The actual
power level then is +6. 5 dBm C+17.3 dBm +
(-10.8 dBm)j.
For Option 01-651B which has the dBm scale
of the output monitor referenced to 1 milliwatt
into 600 Cl use the 600 Cl output impedance
line of graph of Figure 3-2.
For Option 02-651B which has the dBm scale
of the output monitor referenced to 1 milli¬
watt into 75 S2 use the 75 £7 output impedance
line of graph of Figure 3-2.
01810-2
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