DS345 Manual
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II. Staff Sign-off Sheet (OPT)
III. Error Analysis Notes
V. Optical Signal vs Temperature
VII. DS345 Manual
The following is taken from the DS345 manual, which is given is full in the reprints; for more detail on the 345, consult the reprints.
SWEEPS AND MODULATION
Introduction
This section of the manual describes the DS345's modulation capabilities. The DS345 has extremely powerful and flexible built-in modulation functions. It is capable of AM (both simple and double sideband suppressed carrier (DSBSC)), FM, PM, tone bursts, and frequency sweeps. The modulation waveform may be a sine, square, ramp, or triangle wave. Frequency can be swept up or down at a linear or logarithmic rate. A built-in trigger generator al-lows triggering of single sweeps and bursts. For additional flexibility the DS345 can also modulate the output waveform with an arbitrary pattern of amplitude, frequency, or phase values.
MODULATION ON/OFF
The SWEEP ON/OFF key enables the DS345's modulation functions. Press-ing the key toggles the modulation status. When modulation is on the [MOD/SWP] LED will light. When modulation is enabled the modulation type and modulation parameters are checked for consistency with the selected output function. If the selected modulation is illegal (for example, FM frequen-cy out of range for the function) the DS345 will display an error message and not enable the modulation. The erroneous value must be changed before the modulation is turned on.
MODULATION TYPE
The type of modulation is selected using the MODULATION TYPE [UP/ DOWN] arrow keys. Most of the output functions can be modulated by any type of modulation. However, NOISE can only be modulated by the external AM input, and ARB waveforms can only be modulated by AM and BURST modulations. If an invalid choice is selected the message "funct error" is displayed.
MODULATION WAVEFORM
The waveform of the modulating function is selected with MODULATION WAVEFORM UP/DOWN arrow keys. If no LEDs are lit the selected modula-tion type has no associated waveform (BURST, for example, has no modula-tion waveform). Not all modulation types may use all modulation waveforms. The allowable combinations are listed on the following page. Note that ARB modulation waveforms can only be downloaded via the computer interfaces.
If no waveform has been downloaded when this modulation is enabled the message "arb corrupt" will be displayed (see the ARBITRARY MODULATION section).
| WF Type | Single | Ramp | Triangle | Sine | Square | Arb | None |
| Linear Swp | Yes | Yes | Yes | No | No | No | No |
| Log Swp | Yes | Yes | Yes | No | No | No | No |
| AM | No | Yes | Yes | Yes | Yes | Yes | No |
| FM | No | Yes | Yes | Yes | Yes | Yes | No |
| PM | No | Yes | Yes | Yes | Yes | Yes | No |
| Burst | No | No | No | No | No | No | Yes |
MODULATION RATE
Pressing [RATE] displays and sets the modulation rate. Use the keypad and unit indicators of Hz, kHz, or MHz (or the MODIFY up/down keys) to set the modulation rate.
The modulation rate is the frequency of the modulation waveform. For example, if the modulation type is AM, the waveform a sine wave, and the rate 1 kHz the modulating waveform will be a 1 kHz sine wave. For sweeps the modulation rate is the inverse of the sweep time (ie., a 10ms sweep would be entered as 100 Hz). Burst modulation has no associated modulation rate and the message "not applic" is displayed if [RATE] is pushed.
The modulation rate has a range of 0.001 Hz to 10 kHz for AM, FM, and PM. The range for sweeps is 0.001 Hz to 1 kHz (1000s to 0.001s sweep time). The modulation rate may be set with two digits of resolution. If the modulation waveform is set to ARB (AM ARB, FM ARB, or PM ARB) the modulation rate has a different meaning. See the ARBITRARY MODULATION section for more details.
AMPLITUDE MODULATION
Introduction
The DS345 has the ability to amplitude modulate its function output with both the internal modulation generator and an external analog voltage. The inter nal modulation generator may modulate the output with a sine, square (pulse modulation), triangle, ramp, or arbitrary modulation pattern. The external modulation may be either simple AM or Double Sideband Suppressed Carri er (DSBSC) modulation.
External AM Source
The rear-panel AM INPUT is active at all times (even in concert with any oth- er modulation type). The AM INPUT has an input voltage range of ±5V. A +5V input produces an output that is 100% of the programmed value, a 0V input turns the output will off (0%), and at -5V input produces an output that is -100% of the programmed output (a 180° phase change). Applying voltag es from 0 to 5V will result in simple AM. If the voltages are balanced around zero (from -5V to +5V) DSBSC modulation will result (for good carrier sup pression the modulating signal must have an average value of zero). The AM INPUT has a bandwidth of about 20 kHz.
INTERNAL AM
The internal modulation generator can modulate any of the DS345's output functions except NOISE. The modulating waveform may be a sine, square, triangle, ramp, or arbitrary pattern. The rear-panel MODULATION OUTPUT outputs a signal corresponding to the amplitude control voltage. 100% of the output amplitude will produce an output of +5V, zero output will produce 0V, and -100% output will produce -5V out.
Modulation Depth
Press [DEPTH] to display and set to the AM modulation depth. The value may be set using the keypad and % units key, or the MODIFY keys. This val ue has a range of ±100% with 1% resolution. Positive values (0 to100%) will set simple AM with a modulation percentage equal to the DEPTH. Zero per cent depth corresponds to no modulation, while 100% depth corresponds to modulating the output from full off to full on. Negative values (-1% to -100%) will set DSBSC modulation with a modulation percentage equal to the depth.
Modulation Rate
Press [RATE] to display and to set the frequency of the modulating function. The frequency may be set with two digits of resolution from 0.001 Hz to 10 kHz.
FREQUENCY MODULATION
Introduction
The DS345 is capable of frequency modulating any of its output functions, except NOISE and ARB, using its internal modulation generator. The modu lation waveform may be a sine, square (FSK), triangle, ramp, or an arbitrary pattern. The rear-panel MODULATION OUTPUT outputs a signal with 0V corresponding to the smallest frequency output and +5V corresponding to the largest frequency output.
Frequency Span
During FM the DS345 outputs a signal whose frequency range is centered about the programmed frequency. SPAN sets the amount that the frequency varies from the center frequency. The minimum frequency output will be the center frequency - SPAN/2, while the maximum frequency will be the center frequency + SPAN/2. The value SPAN/2 is commonly called the deviation (that is, SPAN = Deviation x 2). The SPAN is displayed and set by pressing [SPAN]. The SPAN may be set with 1 µ Hz resolution, and has a limited range such that the output frequency is always greater than zero and less than or equal to the maximum allowed for the function selected (30.2 MHz for sine and square, 100 kHz for triangle and ramp).
Modulation Rate
Pressing [RATE] displays and sets the frequency of the modulating function. The frequency may be set with two digits of resolution from 0.001 Hz to 10 kHz.
PHASE MODULATION
Introduction
The DS345 is capable of phase modulating any of its output functions, except NOISE and ARB, using its internal modulation generator. The modulation waveform may be a sine, square (PSK), triangle, ramp, or arbitrary pattern (see ARBITRARY MODULATION section for information about ARB patterns). The rear-panel MODULATION OUTPUT outputs a signal with 0V corresponding to the largest negative phase deviation and +5V corresponding to the largest positive phase deviation.
Phase Span
During PM the DS345 outputs a signal whose frequency is centered about the programmed frequency. SPAN sets the amount that the phase varies rel-ative to zero phase. The minimum phase shift output will be -SPAN/2, while the maximum phase shift output will be +SPAN/2. The value SPAN/2 is com-monly called the deviation (that is, SPAN = Deviation x 2). The SPAN is dis-played and set by pressing [SPAN]. The value of the SPAN may be set with 0.001° resolution with a range of 0° to 7199.999°.
Modulation Rate
Press [RATE] to display and set the frequency of the modulating function. The frequency may be set with two digits of resolution in the 0.001 Hz to 10 kHz range.
BURST MODULATION
Introduction
The DS345 generates tone bursts of any of its periodic output functions. The frequency of the output function is limited to 1 MHz for sine and square waves, 100 kHz for triangles and ramps, and no limits for ARBs. When a trig-ger signal is received the DS345 initiates a burst starting at a specific point (phase) in the output waveform, outputs the exact number of programmed waveform cycles, and then stops. The rear-panel TRIGGER OUTPUT gener-ates a TTL compatible signal that goes high when the burst is triggered and low when the burst is complete. This signal may be used to synchronize ex-ternal equipment to the burst. The SYNC output is not active during tone bursts.
Burst Count
The number of complete cycles in a burst is set by pressing [SHIFT][BRST CNT]. The number may be set from 1 to 30000 cycles. The maximum time for a complete burst is 500s, the time for a burst is easily computed from the following formulas:
for sine, square, triangle, ramp
for ARB
Waveform Starting Point
The point in the waveform at which the burst starts (the phase) may be adjusted for sine, square, triangle, and ramp waves. For ARBs the burst always starts on the first waveform point. Changing the PHASE changes the point at which the burst starts. 0.000 degrees phase corresponds to the positive zero crossing of the function, and values up to 359.999 degrees increment through the waveform. PHASE values larger than 360 degrees are set to modulo 360 degrees.
Triggering a Burst
Burst modulation is a triggered function, and therefore a signal needs to ini-tiate the burst. The trigger generator can initiate a burst from the front panel [TRIG] key, the internal rate generator, the external trigger input, or the pow-er line frequency. Setting the trigger generator is detailed in the TRIGGER GENERATOR section (2-22). The TRIG'D LED flashes green each time a burst is triggered. If the DS345 is triggered before the previous burst is com-plete the TRIG'D LED flashes red, indicating a trigger error. At high trigger rates a combination of triggers (green) and trigger errors (red) can make the TRIG'D LED appear orange. Once a burst is triggered the DS345 will ignore all other triggers until the burst is complete.
FREQUENCY SWEEPS
Introduction
The DS345 can frequency sweep its function output for sine, square, triangle, and ramp waves. The sweeps may be up or down in frequency, and may be linear or log in nature. The frequency changes during the sweep are phase continuous and the sweep time may be set between 0.001 and 1000 sec-onds. The DS345 has an analog SWEEP output that may be used to drive an x-y recorder or oscilloscope, a TTL BLANK/LIFT output that can lift a chart recorder pen during the sweep retrace, and a TTL MARKER output that may be set to make transitions at two programmable frequencies during the sweep.
Sweep Type
Pressing the MODULATION TYPE UP/DOWN ARROW keys sets the sweep to either a linear or log sweep. The output frequency in a linear sweep chang-es linearly during the sweep time. The output frequency in a log sweep changes exponentially during the sweep time, spending an equal amount of time in each decade of frequency. For example, in a sweep from 1 kHz to 100 kHz, the sweep will spend half the time in the 1 kHz to 10 kHz range and half the time in the 10 kHz to 100 kHz range). It should be noted that these are digital sweeps, and that the sweep is actually composed of 1500 to 3000 discrete frequency points, depending on the sweep rate.
Sweep Waveform
The DS345's sweep waveform may be set to single, triangle, or ramp using the MODULATION WAVEFORM UP/DOWN arrow keys. With the SINGLE setting the DS345's output frequency will be the sweep start frequency until a trigger is received. The output will then sweep to the stop frequency, reset to the start frequency and wait for another trigger (see the TRIGGER GENERA-TOR section for setting the trigger source). If the waveform is set to a RAMP the DS345 will sweep from the start to the stop frequency, jump back to the start frequency, and repeat continuously. If the waveform is a TRIANGLE the DS345 will sweep from the start to the stop frequency, sweep back from the stop frequency to the start frequency, and repeat continuously.
Sweep RATE/Time
The duration of the sweep is set by [RATE], and the value is entered or modified with the keypad. The sweep rate may be set over the range of 0.001 Hz to1 kHz. The sweep rate is the inverse of the sweep time, a 0.001 Hz rate is equal to a 1000s sweep time, and a1 kHz rate is equal to a 1 ms sweep time. For a TRIANGLE sweep the sweep time is the total time to sweep up and down.
SWEEP FREQUENCIES
The DS345 may sweep over any portion of its frequency range:1 µ Hz to 30.2 MHz for sine and square waves, and 1 µ Hz to 100 kHz for triangle and ramp waves. There are no restrictions on minimum or maximum sweep span. The DS345's sweep range may be set by entering either the start and stop frequencies, or the center frequency and span. The relationships between the frequencies are: Center Frequency = (Stop Frequency + Start Frequency) / 2 Span = Stop Frequency - Start Frequency Start Frequency = Center Frequency - Span/2 Stop Frequency = Center Frequency + Span/2
Start and Stop Frequencies
To enter the sweep start frequency press [START FREQ]. Set the stop fre-quency by pressing [SHIFT][STOP F]. The start and stop frequencies may have any values that are allowed for the displayed waveform. If the stop fre-quency is greater than the start frequency the DS345 will sweep up, while if the start frequency is larger the DS345 will sweep down.
Center Frequency and Span
To set the sweep center frequency press [SHIFT][SWP CF]. The center fre-quency may be set to any value allowed for the displayed waveform. Set the sweep span by pressing [SPAN]. The span value is restricted to sweep fre-quencies greater than zero and less than or equal to the maximum allowed frequency. If the span is positive the DS345 will sweep up, if it is negative the DS345 will sweep down. The MODIFY keys may be used to change the span: pressing [MODIFY UP] will double the span, while pressing [MODIFY DOWN] divides the span in half. The MODIFY keys affect the span in oc-taves–the size of the step is the value displayed by the step size. When the center frequency is changed the span is held constant, while changing the span holds the center frequency constant. If the center frequency or span is changed such that the sweep frequencies are out of the allowed range an er-ror will be displayed on the front panel.
SWEEP MARKERS
The DS345 has two sweep markers that may be used to indicate any two fre-quencies in the sweep. The MARKER output is a TTL compatible signal that goes high when the sweep frequency crosses the start marker frequency and low when the sweep frequency crosses the stop marker frequency. In a trian-gle sweep the markers are only active on the up sweep. The marker positions may be set by entering the marker start and stop frequencies, or the center frequency and span.
Marker Start and Stop
The marker start and stop frequencies are independent of each other and are set by pressing [SHIFT][MRK START] and [SHIFT][MRK STOP] respectively. The frequencies can be set to any value from 1 µ Hz to 30.2 MHz. If the mark-er start frequency is lower than the marker stop frequency the MARKER out-put will initially be low, go high when the sweep crosses the start marker posi-tion, and go low again when the sweep crosses the stop marker position. If the marker start frequency is greater than the marker stop frequency the MARKER output will be initially high, go low when the sweep crosses the stop marker position, and go high again when the sweep crosses the start marker position. If either of the marker positions are outside of the sweep range the marker output will behave as if the sweep had crossed its position. These cases are shown in the diagram below:
Marker Center and Span
The markers may also be set by the center frequency and span (width) of the marked region. Pressing [SHIFT][MRK CF] and [SHIFT][MRK SPAN] respec-tively sets the center frequency and span. The center frequency may have any value from 1 µ Hz to 30.2 MHz range. The span may be any value such that the marker frequencies are greater than zero and less than or equal to 30.2 MHz. If the span is positive the marker start position will be below the stop position, while if the span is negative the marker start position will be greater than the stop position. If the MODIFY keys are used to change the span- pressing [MODIFY UP] will double the span, and pressing [MODIFY DOWN] will divide the span in half. When the center frequency is changed the span is held constant, while changing the span holds the center frequen-cy constant. If the center frequency or span is changed such that the marker frequencies are out of the allowed range an error will be displayed.
Marker to Span
Pressing [SHIFT][MRK=SPAN] sets the positions of the markers to the extremes of the sweep span. The marker start frequency will be set to the sweep start frequency, and the marker stop frequency will be set to the sweep stop frequency. This function is useful for finding the markers when setting up a sweep.
Span to Marker
Press [SHIFT][SPAN=MRK] to set the sweep span to the marker positions. Now the sweep start frequency will be set to the marker start frequency, and the sweep stop frequency will be set to the marker stop frequency. This function can be used to "zoom in" on a marked section of the sweep. If this function sets the sweep frequencies to a value not allowed for the selected waveform, an error will be generated and the sweep disabled.
SWEEP OUTPUT
The rear-panel SWEEP output is a 0–10 V analog output that ramps linearly during a sweep. The output voltage is 0V at the sweep start frequency, and 10V at the sweep stop frequency (during TRIANGLE sweeps the SWEEP output will go from 0V to 10V to 0V). This output may be used to drive a chart recorder or x-y oscilloscope.
BLANK/LIFT OUTPUT
This is a TTL compatible output that is low during the upsweep of a sweep and high during the during the downsweep or sweep reset. This output may be used to blank the retrace of an x-y oscilloscope, or lift the pen on a chart recorder.
