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| d2:offset_phase_lock_servo [2017/10/12 00:42] – [Back-panel Section] Michael Radunsky | d2:offset_phase_lock_servo [2023/11/16 00:02] (current) – external edit 127.0.0.1 |
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| <WRAP right round box 260px> | <WRAP right round box 260px> |
| [{{ :d2:d2-135:offset_servo_small.jpg?nolink&240 |D2-135 Offset Phase Lock Servo (OPLS)}}] | [{{ d2:d2-135:135-side-on-view-lr.png?nolink&240 |D2-135 Offset Phase Lock Servo (OPLS)}}] |
| </WRAP> | </WRAP> |
| ======Offset Phase Lock Servo ====== | ======Offset Phase Lock Servo ====== |
| Please read [[:limited_warranty|Limited Warranty]] and [[:warnings_cautions|General Warnings and Cautions]] prior to operating the D2-135. | Please read [[:limited_warranty|Limited Warranty]] and [[:warnings_cautions|General Warnings and Cautions]] prior to operating the D2-135. |
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| [[d2:quick_start_opls|A quick-start guide]] is available for the D2-135. | [[d2:quick_start_opls|A quick-start guide]] is available for the D2-135.\\ |
| | [[https://www.vescent.com/products/electronics/d2-135-offset-phase-lock-servo/|D2-135 Web page]] |
| =====Description===== | =====Description===== |
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| <imgcaption opls_schematic|Schematic of the D2-135 Offset Phase Lock Servo, D2-160 Beat Note Detector, and D2-150 Heterodyne Module>{{ :d2:d2-135:block_diagram.png?600|}}</imgcaption> | <imgcaption opls_schematic|Schematic of the D2-135 Offset Phase Lock Servo, D2-160 Beat Note Detector, and D2-150 Heterodyne Module>{{ :d2:d2-135:block_diagram.png?600|}}</imgcaption> |
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| A schematic of the OPLS, along with the [[d2:beat_note_detector|D2-160]] Beat Note Detector and [[d2:heterodyne_module|D2-150]] Heterodyne module is shown in <imgref opls_schematic>. The key component in the OPLS is a phase-frequency detector (PFD). The PFD compares the phase and frequency of the divided-by-N beat note to the reference frequency. The PFD outputs a signal proportional to the phase difference between the two input frequencies when there are no phase-slips between the two signals. This output provides a true phase-lock error signal. When there are phase slips, the PFD acts as a frequency comparator, aiding initial lock-up and enabling the OPLS to function as a //frequency//// ////offset//// ////lock// for laser sources with significant phase noise such as DFB and DBR laser diodes. The output of the PFD is fed to a charge pump and finally to the loop filter, where it is then fed back to the slave laser to control the frequency of the beat note. | A schematic of the OPLS, along with the [[d2:beat_note_detector|D2-160]] Beat Note Detector and [[d2:heterodyne_module|D2-150]] Heterodyne module is shown in <imgref opls_schematic>. The key component in the OPLS is a phase-frequency detector (PFD). The PFD compares the phase and frequency of the divided-by-N beat note to the reference frequency. The PFD outputs a signal proportional to the phase difference between the two input frequencies when there are no phase-slips between the two signals. This output provides a true phase-lock error signal. When there are phase slips, the PFD acts as a frequency comparator, aiding initial lock-up and enabling the OPLS to function as a //frequency//// ////offset//// ////lock// for laser sources with significant phase noise. The output of the PFD is fed to a charge pump and finally to the loop filter, where it is then fed back to the slave laser to control the frequency of the beat note. |
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| The loop filter has user-adjustable proportional-integral-differential (PID) feedback and an additional high-frequency roll-off frequency. Tuning the values of the PID loop filter allows the user to optimize the feedback to the laser for best offset locks. This is further discussed below. | The loop filter has user-adjustable proportional-integral-differential (PID) feedback and an additional high-frequency roll-off frequency. Tuning the values of the PID loop filter allows the user to optimize the feedback to the laser for best offset locks. This is further discussed below. |
| The D2-135 comes in two different versions: | The D2-135 comes in two different versions: |
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| *//D2-135-SMA - //SMA input of the electrical beat-note | *//D2-135-SMA// SMA input of the electrical beat-note |
| *//D2-135-FC-800// - Fiber-input of optical beat-note for wavelengths 750nm - 870nm (obsolete) | *//D2-135-FC-800// - Fiber-input of optical beat-note for wavelengths 750nm - 870nm (obsolete) |
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| The D2-135-SMA requires an electrical signal input between 10 and -10 dBm of power. | The D2-135-SMA requires an electrical signal input between 10 and -10 dBm of power. |
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| The D2-135-FC-800 is no longer available, but information regarding it is retained for those users who have purchased this model. It includes a 10 GHz GaAs high-speed photo-detector for converting the input optical beat-note into a electrical beat-note. The maximum optical input power is 1 mW. //Warning: input powers over 1mW of optical power can damage the OPLS.// A minimum of 50 μW of power in the optical beat-note is required(( Note the power in the beat-note is not the same as total power. Because the optical input uses multi-mode fiber, the spatial mode overlap between the two lasers is not guaranteed. If the overlap between the two lasers is poor, there can be very little power in the beat-note despite large optical power. )). | The D2-135-FC-800 is no longer available, but information regarding it is retained for those users who have purchased this model. It includes a 10 GHz GaAs high-speed photo-detector for converting the input optical beat-note into a electrical beat-note. The maximum optical input power is 1 mW. //Warning: input powers over 1mW of optical power can damage the internal photodetector.// A minimum of 50 μW of power in the optical beat-note is required(( Note the power in the beat-note is not the same as total power. Because the optical input uses multi-mode fiber, the spatial mode overlap between the two lasers is not guaranteed. If the overlap between the two lasers is poor, there can be very little power in the beat-note despite large optical power. )). |
| ===== Absolute Maximum Ratings ===== | ===== Absolute Maximum Ratings ===== |
| Note: All modules designed to be operated in laboratory environment | Note: All modules designed to be operated in laboratory environment |
| =====Specifications===== | =====Specifications===== |
| <WRAP center round box 550px> | <WRAP center round box 550px> |
| | | **Value** | **Units** | | | | **Value** | **Units** | |
| |**Min Offset Frequency**(( Low frequency beat-notes are in principle possible with the D2-135-SMA provided the low-frequency beat-note is a square-wave and not sine-wave input and that the loop bandwidth ~10 times lower than your reference frequency. ))| <250 | MHz | | | **Min Offset Frequency**(( Low frequency beat-notes are in principle possible with the D2-135-SMA provided the low-frequency beat-note is a square-wave and not sine-wave input and that the loop bandwidth ~10 times lower than your reference frequency. )) | <250 | MHz | |
| |**Max Offset Frequency**| Min: 9.5, Typical: 10(( Maximum Offset Frequency depends on power of input beat-note signal.)) | GHz | | | **Max Offset Frequency** | Min: 9.5, Typical: 10(( Maximum Offset Frequency depends on power of input beat-note signal.)) | GHz | |
| |**VCO drift**| 200 | ppm/°C | | | **VCO drift** | 200 | ppm/°C | |
| |**PFD Noise**(( See [[#calculating_phase_noise|Calculating Phase Noise section]] for a full description))| -213 | dBc/Hz | | | **PFD Noise**(( See [[#calculating_phase_noise|Calculating Phase Noise section]] for a full description)) | -213 | dBc/Hz | |
| |**ω**<sub>**I**</sub>** **(Integral/Prop. zero)| 4,8,16,32,64,125,250,500 | kHz | | | **ƒ**<sub>**I**</sub>** **(Integral/Prop. corner) | 4,8,16,32,64,125,250,500 | kHz | |
| |**ω**<sub>**D**</sub>** **(Proportional/diff. zero)| 16,32,64,125,250,500,1000,off | kHz | | | **ƒ**<sub>**D**</sub>** **(Proportional/diff. corner) | 16,32,64,125,250,500,1000,off | kHz | |
| |**ω**<sub>**HF**</sub>** **(high freq. cutoff pole)| 0.25, 0.5, 1,2,4,8,16,off | MHz | | | **ƒ**<sub>**HF**</sub>** **(high freq. cutoff pole) | 0.25, 0.5, 1,2,4,8,16,off | MHz | |
| |**Servo Output Range**| ±10 | V | | | **Servo Output Range** | ±10 | V | |
| |**Electronics Input / Output Impedance**| 50 | Ω | | | **Electronics Input / Output Impedance** | 50 | Ω | |
| |**User Adjustable Gain**(( Not including internal gain compensation for N divider. See [[#understanding_gain_in_the_opls|Understanding Gain in the OPLS]] for more details.))| 0 to -76 | dB | | | **User Adjustable Gain**(( Not including internal gain compensation for N divider. See [[#understanding_gain_in_the_opls|Understanding Gain in the OPLS]] for more details.)) | 0 to -76 | dB | |
| |**Max Electronic Beat-Note Input \\ (D2-135-SMA)**| 10 | dBm | | | **Max Electronic Beat-Note Input \\ (D2-135-SMA)** | 10 | dBm | |
| |**Min Electronic Beat-Note Input \\ (D2-135-SMA)**| -10 | dBm | | | **Min Electronic Beat-Note Input \\ (D2-135-SMA)** | -10 | dBm | |
| |**Min Electronic Beat-Note S/N \\ (D2-135-SMA)**| >50 | dB | | | **Min Electronic Beat-Note S/N \\ (D2-135-SMA)** | >50 | dB | |
| |**Max Optical Beat-Note Input \\ (D2-135-FC; obsolete)**| 1 | mW | | | **Max Optical Beat-Note Input \\ (D2-135-FC; obsolete)** | 1 | mW | |
| |**Min Optical Beat-Note Input \\ (D2-135-FC; obsolete)**((Approximate value as exact value depends on wavelength of the light and spatial overlap between the lasers.))| 50 | μW | | | **Min Optical Beat-Note Input \\ (D2-135-FC; obsolete)**((Approximate value as exact value depends on wavelength of the light and spatial overlap between the lasers.)) | 50 | μW | |
| |**Front-panel Input Connection\\ (D2-135-FC; obsolete)((D2-135-FC was shipped with an FC to SC multimode patch cord))**| SC | | | | **Front-panel Input Connection\\ (D2-135-FC; obsolete)((D2-135-FC was shipped with an FC to SC multimode patch cord))** | SC | | |
| |**Front-panel Input Connection\\ (D2-135-SMA)**| SMA | | | | **Front-panel Input Connection\\ (D2-135-SMA)** | SMA | | |
| |**External Reference Input Range**| -10 to +10 | dBm | | | **External Reference Input Range** | -10 to +10 | dBm | |
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| </WRAP> | </WRAP> |
| =====Modes===== | =====Modes===== |
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| The OPLS operates in 12 different modes, controlled by the front-panel knob or with external inputs to the back-panel. These 12 modes select the value of the divide-by-N (N=8,16,32, or 64) and select between three states for the reference frequency (external input, internal VCO High, internal VCO Low). The table below shows the offset frequency ranges for these 12 different modes. | The OPLS operates in 12 different modes, controlled by the front-panel knob or with external inputs to the back-panel. These 12 modes select the value of the divide-by-N (N=8, 16, 32, or 64) and select between three states for the reference frequency (external input, internal VCO High, internal VCO Low). The table below shows the offset frequency ranges for these 12 different modes. |
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| <WRAP center round box 70%> | <WRAP center round box 70%> |
| ^ ^^ N=8 ^ N=16 ^ N=32 ^ N=64 ^ | ^ ^^ N=8 ^ N=16 ^ N=32 ^ N=64 ^ |
| ^ Reference \\ Frequency \\ Setting ^External |250 - 1,920|480 - 3,840|960 - 7,680|1,920 - 10,000| | ^ Reference \\ Frequency \\ Setting ^External |250 - 1,920|480 - 3,840|960 - 7,680|1,920 - 10,000| |
| ^:::^External Reference Input Frequency |30 - 240|||| | ^:::^External Reference Input Frequency |30 - 240 MHz|||| |
| ^:::^Internal VCO Low |385 - 850|770 - 1,700|1,540 - 3,400|3,080 - 6,800| | ^:::^Internal VCO Low |385 - 850|770 - 1,700|1,540 - 3,400|3,080 - 6,800| |
| ^:::^Internal VCO High |770 - 1,700|1,540 - 3,400|3,080 - 6,800|6,160 - 10,000| | ^:::^Internal VCO High |770 - 1,700|1,540 - 3,400|3,080 - 6,800|6,160 - 10,000| |
| ===Error Signal (AC)=== | ===Error Signal (AC)=== |
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| This is an unfiltered version of Error Signal (DC) that is four times smaller, and has a DC offset. When phase locked, the output is 1.6V+2.8<sup>mv</sup>/<sub>deg</sub>*θ, where θ is the phase-error in degrees. When in frequency mode, the output is 1.6V±1V*(1-f<sub>small</sub>/(2 f<sub>big</sub>)). | This is an unfiltered version of Error Signal (DC) that is four times smaller, and has a DC offset. When phase locked, the output is 1.6V+2.8<sup>mV</sup>/<sub>deg</sub>*θ, where θ is the phase-error in degrees. When in frequency mode, the output is 1.6V±1V*(1-f<sub>small</sub>/(2 f<sub>big</sub>)). |
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| ===Ref Freq=== | ===Ref Freq=== |
| **Coarse Gain (eight-position switch)** | **Coarse Gain (eight-position switch)** |
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| The COARSE GAIN sets the overall proportional gain of the circuit without changing the location of any zeros or poles in the loop filter transfer function. The coarse gain adjusts in steps of 6 dB from 0 dB to -42 dB. | The COARSE GAIN sets the overall proportional gain of the circuit without changing the location of any corners or poles in the loop filter transfer function. The coarse gain adjusts in steps of 6 dB from 0 dB to -76 dB. |
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| **Servo Output** | **Servo Output** |
| ====Right Side Panel ==== | ====Right Side Panel ==== |
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| <imgcaption opls_side_panel center|Schematic of the OPLS right-side panel,showing the configurable transfer functino and its user-controls.>{{ :d2:d2-135:d2-135_side_panel.jpg?nolink&700 |}}</imgcaption> | <imgcaption opls_side_panel center|Schematic of the OPLS right-side panel,showing the configurable transfer function and its user-controls.>{{ :d2:d2-135:d2-135-side-panel-f-for-freq.jpg?nolink&700 |}}</imgcaption> |
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| The feedback loop is defined by the Gain vs. Frequency plot shown above. ω<sub>I</sub>, ω<sub>D</sub> and ω<sub>HF</sub> define three zeros in the transfer function. ω<sub>I</sub> is the frequency where the gain switches from having integral gain to having proportional gain. ω<sub>D</sub> is the frequency where the gain switches from proportional to differential. ω<sub>HF</sub> is the frequency where the gain begins to fall off at high frequency. ω<sub>I</sub>, ω<sub>D</sub>, and ω<sub>HF</sub> are each controlled by a rotary switch. | The feedback loop is defined by the Gain vs. Frequency plot shown above. ƒ<sub>I</sub>, ƒ<sub>D</sub> and ƒ<sub>HF</sub> define three corners in the transfer function. ƒ<sub>I</sub> is the frequency where the gain switches from having integral gain to having proportional gain. ƒ<sub>D</sub> is the frequency where the gain switches from proportional to differential. ƒ<sub>HF</sub> is the frequency where the gain begins to fall off at high frequency. ƒ<sub>I</sub>, ƒ<sub>D</sub>, and ƒ<sub>HF</sub> are each controlled by a rotary switch. |
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| **Integrator (****ω**<sub>**I**</sub>**)** | **Integrator (****ƒ**<sub>**I**</sub>**)** |
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| Sets the frequency of the integrator (ω<sub>I</sub>). This knob selects between values between 4 kHz and 500 kHz. | Sets the frequency of the integrator (ƒ<sub>I</sub>). This knob selects between values between 4 kHz and 500 kHz. |
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| **Differential (****ω**<sub>**D**</sub>**)** | **Differential (****ƒ**<sub>**D**</sub>**)** |
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| Sets the frequency of the differentiator (ω<sub>D</sub>). This knob selects between values between 16 kHz and 1 MHz and off (no differential gain). | Sets the frequency of the differentiator (ƒ<sub>D</sub>). This knob selects between values between 16 kHz and 1 MHz and off (no differential gain). |
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| **Differential Gain (25-turn trimpot) ** | **Differential Gain (25-turn trimpot) ** |
| Sets the maximum differential gain. 25-turn trimpot adjusts the gain from 5 dB to 15 dB. | Sets the maximum differential gain. 25-turn trimpot adjusts the gain from 5 dB to 15 dB. |
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| **Integrator (****ω**<sub>**HF**</sub>**)** | **Integrator (****ƒ**<sub>**HF**</sub>**)** |
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| Sets the frequency of the high-frequency roll-off (ω<sub>HF</sub>). This knob selects values between 250 kHz and 16 MHz and off. | Sets the frequency of the high-frequency roll-off (ƒ<sub>HF</sub>). This knob selects values between 250 kHz and 16 MHz and off. |
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| **Ramp Master / Slave (Not Shown)** | **Ramp Master / Slave (Not Shown)** |
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| {{ :d2:d-sub_power_pinout.jpg?nolink&150 |}} | {{ :d2:d-sub_power_pinout.jpg?nolink&150 |}} |
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| | While it is infrequent, the D2-005 power supply may occasionally radiate noise from the side of its chassis onto nearby electronics. This only occurs in some system configurations, and will appear as a signal at the frequency of your mains electricity (typically either 50 Hz or 60 Hz). This noise can easily be removed by moving the D2-005 at least 18 inches (45cm) away from other electronics, rotating it 90° such that the sides of the D2-005 face away, or by moving the entire power supply to a different shelf. To accommodate this, all D2-005's are shipped with a 5' DB9 cable as of January 1, 2022. |
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| **Computer Control (9-pin D-sub)** | **Computer Control (9-pin D-sub)** |
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| <WRAP clear></WRAP> | <WRAP clear></WRAP> |
| | \\ |
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| **Ref. Freq. In** | **Ref. Freq. In** |
| **VCO Freq. Adjust** | **VCO Freq. Adjust** |
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| This input is summed in with the VCO TUNE potentiometer to set the voltage to the VCO, and thus the reference frequency when the OPLS is using the internal VCO. The impedance to this input in 1 kΩ and can accept voltages from -10V to +10V and should tune over entire VCO range, provided that the VCO TUNE potentiometer is set in the middle of the VCO range. | This input is summed in with the VCO TUNE potentiometer to set the voltage applied to the VCO, and thus the reference frequency when the OPLS is using the internal VCO. The impedance of this input is 1 kΩ and it can accept voltages from -10V to +10V which will tune the reference frequency over the entire VCO range, provided that the VCO TUNE potentiometer is set in the middle of its range. |
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| =====Understanding Gain in the OPLS===== | =====Understanding Gain in the OPLS===== |
| =====Understanding the Transfer Function===== | =====Understanding the Transfer Function===== |
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| The charge pump in the OPLS outputs a signal proportional to the phase-error and the transfer function is as shown in <imgref opls_side_panel>. However, the OPLS will typically be used to control a //frequency//-tunable device (such as a laser). In this configuration, the effective loop filter is not the one shown in <imgref opls_side_panel>, but includes a extra integration corresponding to converting the phase-error input to a frequency error. Thus, ω<sub>I </sub>sets the frequency transition from single-integration to double-integration and ω<sub>I</sub> from single-integration to proportional feedback. It is important to understand this 'hidden' integrator when configuring the loop filter parameters. | The charge pump in the OPLS outputs a signal proportional to the phase-error and the transfer function is as shown in <imgref opls_side_panel>. However, the OPLS will typically be used to control a //frequency//-tunable device (such as a laser). In this configuration, the effective loop filter is not the one shown in <imgref opls_side_panel>, but includes a extra integration corresponding to converting the phase-error input to a frequency error. Thus, ƒ<sub>I </sub>sets the frequency transition from single-integration to double-integration and ƒ<sub>I</sub> from single-integration to proportional feedback. It is important to understand this 'hidden' integrator when configuring the loop filter parameters. |
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| =====Calculating Phase Noise ===== | =====Calculating Phase Noise ===== |
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| The phase-noise specified in Section 1.3 is referenced to the phase frequency detector (PFD) at 1 Hz. To convert that to the noise measured on the actual beat-note, it must be rescaled with the following formula: | The phase-noise specified in the [[d2:offset_phase_lock_servo#specifications|Specifications]] above is referenced to the phase frequency detector (PFD) at 1 Hz. To convert that to the noise measured on the actual beat-note, it must be rescaled with the following formula: |
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| ''D2-135 Phase-Noise Floor = -213 + 20Log(N) + 10Log(F<sub>REF</sub>)'' | ''D2-135 Phase-Noise Floor = -213 + 20Log(N) + 10Log(F<sub>REF</sub>)'' |
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| where N is the value of the divider and F<sub>REF</sub> is the reference frequency as measured in Hz. For more details, please see [[http://www.vescent.com/2012/calculating-phase-noise-from-the-d2-135/|http://www.vescent.com/2012/calculating-phase-noise-from-the-d2-135/]] . | where N is the value of the divider and F<sub>REF</sub> is the reference frequency as measured in Hz. For more details, please see [[http://www.vescent.com/2012/calculating-phase-noise-from-the-d2-135/|Calculating Phase Noise from the D2-135]]. |
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| =====Help ===== | =====Help ===== |
