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opposed to 30 pF for the 3581A. If a 10:1 voltage divider probe is used with the 3581C, it must have sufficient adjustment range to compensate for the 40 pF shunt capacitance and the capacitance of any input adapter* that is used. The -hp- Model 10003A Voltage Divider Probe is recommended.

3-160. Balanced Bridged. The Balanced-Bridged configuration provides an unterminated, transformer-coupled balanced input. Coupling capacitors between the INPUT 
connector and the balancing transformer provide isolation for dc inputs up to b1 100 V dc. Inputs exceeding ±100 V dc may damage the input circuitry. The maximum ac input level for the bridged input configuration is 35 V rms. The input impedance in Bridge is greater than 12 K ohms and typically 14 K ohms at 1 kHz.

3-161. Balanced Terminated. The Balanced Terminated configuration provides a transformer-coupled balanced input  with an impedance of 600 ohms or 900 ohms. The input impedance is selected by the front panel dBm 900  ohm/LIN - dBm 600 ohm Calibration switch. Note that the 600 ohm or 900 ohm terminating resistor is connected  directly across the input terminals. There is no dc isolation for the termination. The combined ac and dc levels  applied to the terminated input must be such that the power dissipated by the terminating resistance is less than  0.5 watt. With no dc applied, the maximum ac differential input level is + 27 dBm.
*Recommended: Pamona Electronics No. 2798 Type 310 to BNC Adapter, -hp- Part No. 1251-3757.

3-162. Input Connector. The 3581C INPUT connector accepts a Western Electric Type 310 (or equivalent) mating 
plug. See Figure 3-23 for details.

3-163. Tracking Output. The 358 IC has a transformer-coupled; 600 ohm balanced Tracking Oscillator/Restored output. The specified frequency response for this output is b1 0.5 dB from 100 Hz to 20 kHz. The rear panel OUTPUT connector accepts a Western Electric Type 310 (or equivalent) mating plug (Figure 3-23).

3-164. Audio Monitor. The 3581C has a built-in audio amplifier and speaker which allows the operator to listen to 
the Tracking Oscillator or Restored output signal. The selection of Tracking Oscillator or Restored is made using  the rear panel OUTPUT MODE switch. The volume can be adjusted using the AUDIO LEVEL control located  on the front panel. Headphone connectors for the audio monitor are provided on the rear panel of the instrument.  The connectors accept Western Electric Type 310 or Type 241 mating plugs (Figure 3-23). The impedance of the  HEADSET output is 900 ohms, nominal. The maximum output level is 0dBm/900 ohms. The output will drive  headphones with impedances of 8 ohms or greater. The speaker is automatically switched off when a headphone  is plugged in.

3-165. Amplitude Measurements. The 3581C can be calibrated for absolute measurements in dBm/600 ohms or  dBm/900 ohms. The impedance is selected by the front panel dBm 900 ohm/LIN - dBm 600 ohm Calibration  switch. The 3581C does not have a calibrated scale for measurements in dBV. The 3581C log scales can be used  for relative measurements in dB; the linear scales can be used for relative measurements in percent of full scale.

3-166. Manual Compatibility. Except for the special features described previously, the 3581C is identical to the  3581A and most of the information in this section applies to both instruments.

3-167. BASIC OPERATING PROCEDURES.

3-168. Instrument Turn On.

3-169. Power Line Operation.

a. Check the line voltage at the point of installation.

b. Refer to Figure 3-24 and set the 3581 for the line voltage to be used (boy, 120V, 220V or 240 V). Line  voltage must be within + 5% to - 10% of voltage setting.

c. Verify that the proper fuse is installed in the fuse holder: Line Setting Fuse Type  -hp- Part No. 100V/120V 0.5A,250V Normal Blow 2110-0012 220 V/240V 0.25 A, 250V Normal Blow 2110-0004

d. Connect the detachable ac power cord to the rear panel power receptacle and to the power source.

e. Set the POWER switch to the ON (AC) position. The POWER light and the frequency display will illuminate.

f. Allow a warm-up period of at least 5 minutes before using the 3581 in a critical measurement application.

a. Connect the low (black) terminal of the front panel INPUT connector to earth ground or to an appropriate  system ground.

b. Set the POWER switch to the ON (BAT) position. The POWER light and the frequency display will  illuminate.

c. Allow a warm-up period of at least 5 minutes before using the 3581 in a critical measurement application.

d. To recharge the batteries, perform steps a through d of the power-line turn on procedure (Paragraph 3-169).  Set the POWER switch to the CHARGE position. The POWER light will illuminate. The instrument cannot be  used while the batteries are being charged.

Caution

The instrument should not be left in the CHARGE mode for prolonged periods. A charge period of 14 hours is sufficient to recharge a fully discharged battery pack Extended periods of overcharge in ambient temperatures exceeding 3Q0 C (860 F) will severely degrade battery life and capacity by causing the cells to overheat.