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deflection. When the Volts scale is selected, an output of 0 V corresponds to a 0 V meter reading and an output of + 5 V dc corresponds to a full-scale (1 or 3.2) meter reading. When the Log 90 dB scale is selected, the output voltage is scaled to 0.05 V per dB. An output of 0 V corresponds to - 100 dB and an output of + 5 V dc corresponds to 0 dB. When the Log 10 dB scale is selected, the output voltage is scaled to 0.5 V per dB. An output of 0V corresponds to - 10 dB and an output of + 5 V corresponds to 0 dB. The output resistance is a 1 kilohm, nominal.
3-138. Pen Lift Output. The Pen Lift output is provided for use with X-Y recorders having electrically operated penlift circuits through which the pen can be remotely actuated by a contact closure. A contact closure is present across the Pen Lift output terminals during single and repetitive sweeps. The contacts open at the end of each sweep and do not close until after the sweep is reset. This prevents retrace lines from being drawn on the X-Y recording. The Pen Lift output terminals are isolated from case ground.
3-139. Rear Panel Output.

3-140. The rear panel OUTPUT connector is controlled by the OUTPUT MODE switch. With the switch in the TRACKING OSC position, the OUTPUT connector sup plies a constant level 5 Hz to 50 kHz signal that tracks the tuned or swept frequency of the instrument. With the switch in the RESTORED position, the amplitude of the 5 Hz to 50 kHz output signal is proportional to the amplitude of the signal being measured. The constant level Tracking Oscillator signal can be used for making closed loop frequency response measurements. The Restored output allows the 3581 to be used as a narrow band amplifier or bandpass filter.

3-141. The amplitude of the Tracking Oscillator or Re stored output signal can be adjusted using the rear panel LEVEL control. When the output is not terminated or is driving a high impedance load, the signal level can be adjusted from 0V to 2V rms. The 3581 A output is 600 ohms unbalanced while the 3581 C output is 600 ohms balanced. When the output is terminated with a 600 ohm load, the maximum output level is approximately 1 V rms. The specified frequency response for the 3581 A output is ± 3% from 15 Hz to 50 kHz. The specified frequency response for the 3581C balanced output is ± 0.5 dB (± 5%) from 100 Hz to 20kHz. For both the 3581A and the 3581C outputs, the total harmonic distortion and spurious is more than 40 dB below a 1 V signal level.

3-142. The specified frequency accuracy of the output signal is 1 Hz relative to the center of the instrument's passband. This means that on the 3 Hz bandwidth the signal may be near the edge of the passband. This has no effect except when making closed-loop measurements where the tracking oscillator signal is fed into the INPUT through a network under test.  If the frequency is near the edge of the passband, insertion loss will be encountered.  Under worst case conditions, maximum insertion loss is approximately -1.5dB.  Typically, the insertion loss is less than 0.2 dB.

3-143 For most closed-lop measurements optimum results will be obtained using the 10Hz or 30 Hz bandwidth.  If the 3 Hz bandwidth is used, insertion loss can be minimized by performing the Reference Oscillator Frequency adjustment outlined in Section V.

3-144. L.O. Output.  

3-145. The VTO in the 3581 generates a 1 MHz to 1.5 MHz signal which is divided to obtain the 100kHz to 150kHz local oscillator signal that is applied to the Input
Mixer. The 1 MHz to 1.5 MHz VTO signal is available at the rear panel LOCAL OSCILLATOR OUT connector. The amplitude of the L.O. output signal is approximately
100 mV rms; output impedance is 1 kilohm, nominal.  

3-146. If frequency resolution greater than 1 Hz is required, the tuned frequency of the instrument can be measured with an electronic counter connected to the L.O.
output. Measurement accuracy is ± 5 Hz. The following formula can be used to calculate the tuned frequency from the counter reading:

  Ft = (Fc/10) - 100k Hz
Where:
  Ft = tuned frequency
  Fc = counter reading

3-147. The tuned frequency can also be measured using the 5 Hz to 50 kHz Tracking Oscillator signal. However, it is generally preferable to use the L.O. output signal because it can be measured with a 0.1 second gate time for fast response. 

3-148 L.O. Output

3-149.  The 3581 can be remotely tuned by applying an externally generated L.O. signal to the rear panel LOCAL OSCILLATOR IN connector (MODE switch set it EXT).  An external L.O. signal ranging from 1MHz to 1.5MHz tunes the 3581 from 0 Hz to 50kHz.  The frequncy range of the instrument can be extended to 60kHz by applying a 1.6Mhz L.O. signal.  For measurements between 50kHz and 60kHz, a possible worst-case error of +/- 3dB or +/-30% must be added to the Amplitude Accuracy specifications.

3-150. The amplitude of the external L.O. signal must be within the range of 0.1 V rms to 1 V rms. The impedance of the L.O. Input is 220 ohms, nominal. In order for the 3581 to meet the frequency stability, noise sideband and spurious specifications listed in Table 1-1, the external Local Oscillator must have the same characteristics as the internal Local Oscillator (VTO). These characteristics are:
Frequency Stability: ± 5 Hz per °C
Phase Noise: > 70 dB below L.O. signal level
       ± 10 X BW* away from L.O. frequency
Non-Harmonically
Related Spurious: > 80 dB below L.O. signal level
 

*3581 BANDWIDTH setting

Any frequency drift, phase noise or spurious on the external L.O. signal will appear as if it is introduced by the input signal. Satisfactory results can generally be obtained using an -hp- Model 3320A/B or 3330A/B Frequency Synthesizer as the external L.O. source. Before using an external L.O. for a critical measurement application, check for noise sidebands and spurious using the Performance Test procedures outlined in Section V. In some cases, it may be helpful to run comparison tests between the internal L.O. and the external L.O.


3-151. Option 001.
3-152. The 3581 Option 001 is equipped with an internal rechargeable battery pack and a protective front panel cover for complete portability.

WARNING
To protect operating personnel, the 3581
Option 001 chassis must be grounded. For 
power line operation connect the power cord to a three-prong grounded receptacle. For battery operation connect the common (black) input terminal to earth ground or to an appropriate system ground. If a system ground is used be sure it is actually at ground potential and is not a voltage source.


3-153. The 3581 Option 001 can be operated from the ac  power line or from its own internal battery pack. With the  POWER switch set to the ON (AC) position, the instrument receives its power from the ac power line and a trickle charge is applied to the batteries. The trickle charge prevents the batteries from discharging, but is not sufficient to recharge the batteries in a reasonable time. With the POWER switch in the ON (BAT) position, the ac power is turned off and the instrument receives its power solely from the internal battery pack. A fully charged battery pack will operate the instrument for more than 12 hours. When the batteries are discharged to the point where they cannot operate the instrument properly, the power is automatically shut off. This eliminates erroneous measurements caused by weak batteries and further prevents the batteries from being damaged due to excessive discharge.

3-154. To recharge the batteries, connect the instrument to an appropriate ac power source and set the POWER switch to the CHARGE position. The POWER light will illuminate. The instrument cannot be operated while the batteries are being charged. Recharge time for completely discharged batteries is 14 hours. The useful life of the batteries is more than 100 charge/discharge cycles. The instrument should not be left in the CHARGE mode for prolonged period& 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.


3-155. Temperature Limits. To prevent battery damage, the following temperature limits must be observed:

a. Operating Temperature: 00 C (+ 320 F) to + 40o C (+ 1040 F).
b. Charge Temperature Range: 00C (+ 320 F) to + 400C (+ 1040 F).
c. Storage Temperature Range: - 400 C ( 400 F) to +500C(+ 1220F).

3-156. The 3581C.


3-157. The 3581C is a special version of the 3581 that is designed specifically for communications applications. 
The operating features of the 3581C are described in the following paragraphs.

3-158. Selectable Input Configurations. The 3581C has three selectable input configurations: Unbalanced, 
Balanced Bridged and Balanced Terminated. The selection is made using the front panel slide switch. The three 
input configurations are illustrated in Figure 3-22.

3-159. Unbalanced. The unbalanced input configuration is 4 identical to the single-ended input of the 358 lA. 
Because . of the input switching, however, the shunt capacitance of the 358 IC unbalanced input is approximately 
40 pF as