HP3581_Eight

AM detector, the maximum modulating frequency to which it can respond properly is  approximately 100 Hz for the 300 Hz BANDWIDTH setting.
3-111. Sweep Modes.
3-112. The front panel SWEEP MODE switch permits selection of five sweep modes:

3-113. Repetitive Mode. In the Repetitive sweep mode, the instrument sweeps continuously  over the selected frequency range. The duration of each sweep is determined by the SWEEP TIME setting.

3-114. Single Mode. When the Single sweep mode is selected, the instrument sweeps one time over the selected  frequency range and stops at the end frequency. The instrument remains at the end frequency until another sweep  mode is selected or until a new sweep is initiated. A new sweep can be initiated by setting the SWEEP MODE  switch to RESET and back to SINGLE. If the External Trigger line (Paragraph 3-129) is low when the sweep is  reset, the new sweep will not start until a trigger is applied. However, the single sweep cannot be reset by an  external trigger and must be reset manually.
3-115. The Single sweep mode is particularly useful for making single X97Y recordings where retrace is not  desired. The operator can start the sweep, go about his business and return later to retrieve the completed  recording.
3-116. Reset Mode. When the Reset mode is selected, the sweep generator resets, the X-Axis recorder output  goes to 0 V and the instrument remains at the start frequency indicated on the frequency readout. The front panel  ADJUST light (paragraph 3-124) is operative in the Reset mode, making it a convenient mode to use for setting  sweep parameters.
3-117. Manual Mode. When the Manual mode is selected, the electronic frequency sweep is disabled and  frequency control is transferred to the MANIJAI. VERNIER potentiometer. When the vernier control is fully  counterclockwise, the instrument is at the start frequency set by the FREQUENCY control and the X-Axis  recorder output is at 0 V. As the vernier is rotated in a clockwise direction, the frequency increases and the  X-Axis output voltage increases just as it does with the electronic sweep. When the Vernier is fully clockwise,  the instrument is at the end frequency determined by the FREQ SPAN setting and the X-Axis output is at + 5 V.  Since the manual sweep fully duplicates the span of the electronic sweep, it can be used to calibrate an X97Y  recorder or scope connected to the Recorder outputs. The manual sweep can also be used for fine tuning with the  FREQ SPAN set to 50 Hz.
3-118. Off Mode. When the Off sweep mode is selected, the sweep generator is reset just as it is in the  Reset mode. The only difference is that the front panel ADJUST light is disabled in the Off mode. The Off mode  is a convenient mode to use when manually tuning the analyzer.
3-119. Sweep Time and Sweep Rate.

3-120. Sweep Time Control. The front panel SWEEP TIME control provides 14 sweep time settings ranging from  0.1 second to 2,000 seconds.
3-121. Sweep Rate. The sweep rate in Hz per second is determined by the FREQ SPAN and SWEEP TIME 
settings:

Increasing the frequency span or decreasing the sweep time increases the sweep rate.

3-122. Optimum Sweep Rate. The optimum sweep rate is the maximum rate at which the frequency can be swept  without excessively compressing or skewing the amplitude response. When the 3581 is sweeping at what is  considered to be the optimum rate, the amplitude compression is about 2%.

3-123. The optimum sweep rate is determined by the response time of the instrument. If the response time is long, the sweep rate must be slow so that the instrument can respond properly. The response time of the 3581 is determined by the BANDWIDTH and DISPLAY SMOOTHING settings. Narrowing the bandwidth or increasing 
the display smoothing increases the response time and, therefore, decreases the optimum sweep rate. 

3-124. Optimum Sweep Indicator. The 3581 is equipped with an internal detector that monitors the BANDWIDTH, DISPLAY SMOOTHING, FREQUENCY SPAN and SWEEPTIME control settings. When these control settings are such that the sweep rate exceeds the optimum sweep rate, the front panel ADJUST indicator illuminates.

3-125. To sweep at the optimum rate, select the Reset mode and set the FREQUENCY, FREQUENCY SPAN, BANDWIDTH and DISPLAY SMOOTHING controls to obtain the desired measurement parameters. Then, starting with a slow SWEEP TIME setting, increase the sweep rate until the ADJUST light first comes on. When 
the ADJUST light comes on, rotate the SWEEP TIME control one position counterclockwise. The ADJUST light will go out and the instrument will be set to sweep at the optimum rate.

3-126. For closed-loop measurements where the 3581 is used as a network analyzer, the optimum sweep rate is determined by the 3581 BANDWIDTH and DISPLAY SMOOTHING control settings and by the bandwidth of the network under test. During closed-loop measurements, the input frequency is always near the 
center of the passband and the IF Filter is required to respond only to amplitude variations introduced by the network. For this reason, the optimum sweep rate for closed-loop measurements is generally much faster than it is for open-loop measurements. In many closed-loop measurement applications the sweep rate can be set 3 or 4 positions faster than the optimum rate indicated by the ADJUST light.3-127. If the optimum sweep rate is not limited by the bandwidth of the 3581, it may be limited by the bandwidth of the network under test. For bandpass and low pass filters, a rough approximation of optimum sweep rate can be made using the following formula:

3-131. To remotely trigger the frequency sweep, apply the following levels to the center terminal of the EXT TRIG IN connector:

3-132. The duration of the sweep trigger should be greater than 1 microsecond but less than the total sweep time. When the sweep is triggered in the Single sweep mode the instrument sweeps one time and stops at the end frequency. The sweep must then be reset manually. This can be done by setting the SWEEP MODE switch to RESET and back to SING. If the trigger line is low when the sweep is reset, the new sweep will not begin until a trigger is applied. When the sweep is triggered in the Repetitive sweep mode, the instrument sweeps one time and resets to the start frequency. When the sweep resets, an internal 0.2 sec to 2 sec. delay is 
initiated to allow time for the IF Filter to settle. The sweep cannot be retriggered until after the delay is over. 
This applies to both the Single and Repetitive sweep modes. Table 3-7 lists the approximate delay time for each 
BANDWIDTH setting.

BANDWIDTH DELAY

300 Hz 0.2 sec. 100Hz 0.2sec. 30 Hz 0.2 sec. 10Hz 0.5sec. 3Hz 2 sec.
3-133. Recorder Outputs.
3-134. Recorder outputs are provided on the rear panel of the 3581 to permit the use of an external X-Y recorder/plotter or variable persistance scope. Two instruments recommended for use with the 3581 are:
-hp- Model 703 SB Option 020 X-Y Recorder
-hp- Model 1201A/B Variable Persistance Oscilloscope
Although the Standard Model 7035B and other X-Y recorders can be used, the Option 020 is preferable because it has some special features that simplify scale calibration. In addition, the Model 703 SB Option 020 has an X-Axis log converter which can be used to scale the 3581 linear sweep to provide a full log sweep over a 3-decade (10 Hz to 10 kHz) range.
3-135. X-Axis Output. The X-Axis output supplies a dc voltage proportional to the frequency sweep. When the 
sweep is at the start frequency, the output is 0 V dc; when the sweep is at the end frequency, the output is + 5 V 
dc. The output resistance is 1 kilohm, nominal.
3-1 36. During single and repetitive sweeps, the X-Axis output is a 0 V to + 5 V linear ramp. When the Manual sweep mode is selected, the X-Axis output voltage corresponds to the frequency set by the MANUAL VERNIER control. When the Reset or Off sweep mode is selected, the X-Axis output remains at 0 V.
3-137. V-Axis Output. The Y-Axis output supplies a dc voltage proportional to the meter reading. The output 
level ranges from 0 V to + 5 V dc for zero to full scale meter