Dbm/Voltage Conversion Chart - HP 654A Operating And Service Manual

Model 654A Section III
SECTION III
OPERATING INSTRUCTIONS
3-1. INTRODUCTION.
3-2. This section contains instructions and information
necessary for the operation of the 654A Test Oscillator.
Included in this section are identification of controls,
indicators and connectors, turn-on procedure, meter
mechanical zero adjustment and operating instructions.
3-3. CONTROLS, INDICATORS, AND CONNECTORS.
3-4. All operating controls, indicators and connectors of
the 654A are identified and described in Figure 3-1.
3-5. TURN- ON PROCEDURE.
3-6. OUTPUT METER MECHANICAL ZERO
ADJUSTMENT.
3-7. The Model 654A output meter is properly
mechanically zero-set when the meter pointer rests over the
-1 dBm mark. Zero-set the output meter to obtain
maximum accuracy and mechanical stability in the
following manner. With LINE switch turned off, insert
pointed object (such as tip of ball point pen) into recess on
adjustment wheel, and rotate wheel until meter pointer
rests exactly over - 1 dBm mark.
3-8. PRIMARY POWER APPLICATION.
a. Before applying primary power to instrument, set
115 or 230 volt slide switch (S3) to position which
indicates primary voltage to be used.
b. Connect primary power to connector J1. Switch
LINE switch (Si) to ON position; pilot lamp
(DS1) will glow.
3-9. OPERATING INSTRUCTIONS.
a. Zero- set meter (Paragraph 3-7) and turn
instrument on (Paragraph 3-8).
b. Set the FREQUENCY RANGE switch and
FREQUENCY dial (with VERNIER) to the
desired frequency. (Dial reading multiplied by
range setting gives the frequency in Hz.)
c. Connect a frequency counter to the rear panel
COUNTER OUTPUT, if desired.
d. Select the required output impedance by pressing
the appropriate IMPEDANCE pushbutton.
e. Adjust the OUTPUT LEVEL attenuators and the
AMPLITUDE control for the desired signal output
level. The algebraic sum of the meter indication
and the attenuator setting gives the power level, in
dBm, into a load equal to the impedance selected
by the IMPEDANCE pushbutton. In Table 3-1, the
O dBm and + 10 dBm levels are converted to
voltage for each impedance.
SWITCH THE 10 DBM STEP
ATTENUATOR DOWN BEFORE
CONNECTING TO SENSITIVE
EQUIPMENT, SUCH AS THERMAL
CONVERTERS, SO AS TO PREVENT
DAMAGE FROM OVERLOADING.
Table 3-1. dBm/Voltage Conversion Chart
0 dBm = 1 m watt into rated load.
Impedance 0 dBm +10 dBm
50 ohm
75 ohm
135 olun
150 ohm
600 ohm
0.224 V rms
0.274 V rms
0.367 V rms
0.387 V rms
0.775 V rms
0.707 V rms
0.866 V rms
1.162 V rms
1.225 V rms
2.449 V rms
f. Connect the load to the output connectors. Use
the UNBAL connector for 50 ohm and 75 ohm
loads and both connectors (BAL) for 135 ohm,
150 ohm and 600 ohm loads.
3-10. OPERATING CHECK.
3-11. Before making measurements using the 654A,
perform the following front panel checks to ensure that
your instrument is operating correctly.
a. Turn AMPLITUDE control until white arrow on
knob is pointing up; meter should indicate
approximately 0 dBm.
b. Turn AMPLITUDE control extreme
counterclockwise; meter should indicate - 1 dBm or
less.
c. Turn AMPLITUDE control extreme clockwise;
meter should indicate + 1 dBm or greater.
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