national radio astronomy observatory charlottesville, virginia
Contents
1. lotp 7 v 907 gt P gt S 1 12 2 s pem d 6 40 MAPTOHDT 2o0mv Kk m v K 26 00 v ma 8 o v mA mv DES CONNECTONS M C CARD To RECEIVER SV 75 52 APV D Control and Monitor Data Link 412. Me 010 33133AN03 20 20 01 14 5 JoSt 0401 30 343334 temperatures of Th and exactly controlled 65 457 respectively by the temperature controllers The monitor and control board links the receiver with the computer The computer controls the elevation angle and monitors the receiver s working status and measurement results A reference generator at a frequency of 4 KHz after frequency dividing drives the chopper s motor driver IC SAA 1027 and the synchronous detector and the elevation motor driver IC SAA 1027 is driven by the computer s control signals LOCAL OSCILLATOR Local oscillator power is generated by a commercial 75 GHz Gunn oscillator Millitech Model GDM 12T Some important parameters of the Gunn oscillator which have been carefully examined before being used in the receiver are the frequency stability output power and the effects of load impedance 3 1 TEMPERATURE COEFFICIENT OF THE GUNN OSCILLATOR In order to insure that the receiver will work in summer and in winter the Gunn oscillator must have a good stability with respect to the variation of its physical temperature component plate of the receiver is temperature controlled by a proportionally controlled heater but there may be as much as 15 C variation inside the receiver box for a 20 C to 50 C outside temperature variation Because of the narrow b
3. M s MA 12 2 54 moo t 2 esnem gt 2 e nma ea A OAD SP IS EELS A ES ES OL AD KES ee SMEG dE OR A NP M 24 Fa B p e m eae T lt wee 5 lt ete 2 oo 2 or m m p lt amat comp ape o wm eo e Ens gt F euam wem gt o comes ame wise ee 2 ene e a c ih PL mo o aoe woe oro a dd c Quale CTRL _ _ ___ 2 ew oo oo nme oo 33006 e 9r eee Fig 17 Calibration Result 10 ACKNOWLEDGEMENTS 225 GHz atmospheric receiver system described here was designed by Dr S Weinreb 11 the construction and
4. 4 e I Comparison of the Temperature Coefficients Between the Original and the Improved Gunn Oscillators 2 Fig n p a Relationship of the Tripler Output Power and Bias Voltage and Pump Power 34 Fig voltage and pumping power the backshorts are tuned shown in Figure 3 when the DC bias and the tuning backshorts are optimized the peak conversion efficiency is 5 3 percent Table 1 gives the four triplers optimum bias voltages output powers and the Gunn oscillator pump powers TABLE 1 Tripler Bias and Performance Data Tripler Used in Optimum Pump Number Receiver 4 QUASI OPTICAL SYSTEM The quasi optical system consists of the elevation mirror Ml fixed mirror M2 chopper wheel C and lens L mentioned previously the chopper wheel plays a very important role in the system switches the incident beam sequentially from the sky signal to the reference load 45 C and to the hot load 65 C under the control of the chopper motor driver and the reference generator 4 CHOPPER WHEEL The chopper wheel consists of four blades which are mounted on the surfaces of a cubic block see Figure 8 It rotates around its axis as driven by the stepper motor When the chopper blades
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6. L 904 ANZ ope Od oO QsuUNIZCh MEME Le U F PAWS 0IHVA373 09 HE 107 x b x oo Y 57 lt ez Sie 2 19 as 1 Y 9 cooy NJ sil 828 Z9 Adz word CPI gt m Q lt ES 2 4 222 wiy P o L t 22 14 19 2 5 St e 9 CI 19 When manual control mode matter whether is each push of the MAN DIR switch will toggle the flip flop Q2 therefore the direction changes When in the CPU MODE if Q2 is low Q2 0 the direction DIR CW The direction coincides with the computer s command 02 is high 02 1 DIR The direction is opposite to the computer s command So it is necessary to reset the flip flop Q2 to zero when the computer begins to control the direction This is realized by the OR gate 741502 Its inputs are connected to the computer controlled GZ go to zenith and ST step and its output is connected to the CLR2 of flip flop Q2 Then CLR2 GZ 5 Normally if there is no CPU control command GZ and ST are both zero Then the CLR2 1 When the CPU wants to control the elevation mirror go to zenith or step either GZ or ST gives a positive pulse which will cause a negative pulse at C
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9. 45 C respectively So if we adjust the gain Grcv to make the output of the H R AMP as 200 Grcv Th Tr 200 65 45 4000 Grcv 4000 mV then the gain of the receiver Grcv 1 mV per Kelvin output of the synchronous detector can then be given as 5 20 Ts 318 H 4000 2 Tsys 318 10 000 Here we see that the output of H R is a constant of 4000 mV if the receiver is properly adjusted The reading of H R can also be used to check the system synchronization That is by changing the Ts from room temperature to liquid nitrogen temperature the readings of the should remain constant it changes too much should be less than 20 mV or 0 1 degree the system is out of synchronization Z ELEVATION MIRROR DRIVER The elevation mirror can be either computer controlled or manually controlled Figure 16 is the schematic of elevation mirror driver 7 1 MIRROR SCANNING DIRECTION CONTROL The direction of the elevation mirror scanning 15 controlled by the potential level of the IC chip SAA 1027 s DIRECTION PIN 3 When it is high the mirror will scan in a clockwise CW direction The level is determined by the state of CW controlled by computer and the state of the J K flip flop 741 5109 controlled by manual The direction 15 given as Dir CW Q2 Q2 CW 18 OT 914
10. Projection of the Chopper Wheel the Focal Plane 9 9 F gt ON Fig 8 The Chopper Blade and Mount Block Fig 9 Injection Cavity s Frequency Features with Different Backshort Settings Fig 10 Chopper Wheel Driver Fig 11 Synchronous Controller Fig 12 Waveforms of Signals Fig 13 Motion of the Blade Switches the Beam from the Sky to the Reference Load and the Square Law Detector Output Waveform Fig 14 Angle of the Beam Cut Sactisn Opened to the Chopper Wheel Shaft 20120035 Fig 15 Synchronous Detector Fig 16 Elevation Mirror Driver Fig 17 The Calibration Result APPENDICES Appendix I Photograph and Schematic of Square Law Detector Appendix II Temperature Controller 111 12 Power Supply Converter Appendix IV Connector Wirings Appendix V Layout and Wiring of Wire Meap Card ii 11 13 13 14 15 15 19 21 23 24 26 31 37 225 GHZ ATMOSPHERIC RECEIVER USER S MANUAL Zhong yi Liu ds INTRODUCTION The 225 GHz atmospheric receiver is controlled by a desktop computer The system will automatically start when the 12V DC power supply is turned on All of the sixteen analog monitor points three of them are spare are scanned scaled and the values are displayed on the CRT screen The control commands and some special key functions are also shown at the bottom of the CRT screen 1 Operation of the receiver
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14. Connector on the Receiver Component Plate SR HR R Tour Tw OG 0 9 OO 9 0 49 0 20 2 09 03 04 29 69 C9 69 60 G 63 G3 63 69 69 6 trap Vsup Isup SPARE APIV D Connector on the Receiver Cover 33 Location KE CETVER DOWER _ ATA FROM ECEIVER CONNECTOR 06 28 195 10 DowEe SUPPLY EN 70 o CONNECTOR CABLE IDENTIFICATION TYPE ASSEMBLER DATE PIN COLOR PIN PURPOSE E RCV DATA EES NIMI CND 2 MomTeR x x GAD Dec o NP jam 1 as rs asFssas ESP ed M 1 T LINCOLN 1 Y APIV E Power Supply and Data Link Connector 11 CUNERAL LOCKION RBCEIVER Box To EZ ROK FROM CONNECTOR 53 26 20 275 10 CONNECTOR CABLE IDENTIFICATION c cuiu ASSEMBLER DATE 25 FROM COND TO PIN COLOR PIN PURPOSE 2223 Tuma x uut F CT spy BUE ae 2 2 3 1 LINCOLN LABORA APIV F Receiver to Elevation Mirror Connector J2 35 GLNERAL LOCATION REC
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16. 45 degrees but an angle A which directs the beam to the center of the absorber when the blade is at the focal position see Figure 7 The distance from the focal point to the absorber is 2 125 inches and is 1 30 inches from the center of the absorber to the focal plane angle A is then given by 0 5 90 1 1 30 2 125 29 27 We can now calculate the blade s width W as B Cos A 1 412 The area of the effective reflection area on the fixed mirror surface equals the projection area of the lens on the mirror The radius of the lens is one inch and the focal length F is 2 562 inches When the blade passes the beam the width of the cut section will be d 2 R F 1 2 Sin 29 27 0 269 Now the height of the blade can be determined as h R d 2 2 1 35 see Fig 6 and Fig 8 An optical interruption wheel OIW is located on the same shaft as the chopper wheel There is a narrow slot in the edge of the OIW through which an infrared emitting diode is coupled to a photo transistor When the shaft turns the photo transistor will send out a pulse each turn This pulse is used to synchronize the chopper driver and the synchronous detector The relative position between the chopper wheel and the OIW is carefully adjusted Unless necessary do not readjust Any 11 the absorber was a perfect load it would be possible to make the angle of the blades 45 degrees spurious LO signal emitted f
17. Gunn oscillator G and is then frequency tripled to 225 GHz by the NRAO made tripler T In the injection cavity I the LO power is split into two halves One half of the LO power is combined with the signal received by the feed horn and injected into the mixer M the other half is a spurious signal emitted into the sky by the feed horn The 1 5 GHz IF signal is amplified by amplifiers 1 and AMP2 and is filtered by bandpass filter F The chopped 1 5 GHz IF signal drives the square law detector and DC amplifier with output proportional to the power or temperature of the total signal entering the mixer The output of the square law detector is synchronously detected by the synchronous detectors to give outputs proportional to Ts Tr Th Tr and Tr Tsys where Tsys is the system effective noise temperature output Th Tr is used for absolute gain calibration of the system The 83 1323 2 9 622 3 1 40 0 32018 1 380914 div 114405 1019 11938 41 9 18 250 NN09 40193130 1 9 1250 5 u3ldIul NNNS 204 7130 1 705 31 t3 4 NYOH 4 1 1 51 1 0333 262 Su 1041802 YOLINOW anan 190 ONAS OL Ww 4 29 p 415 s LVY3N39 NOIlVA313 324383338 YOLOW dOHI QVO 10H 53018 r 4 23 3440 2 4 NTLVLOY NOILVAI13 OL ah Hod
18. Law Detector eis gt 4 15 gt IS a 26 am _ 1 lt SO E t 1 lt lt mr 13 Y oZ PA lt lt gt gt SQUARE CET ECTER K G i 4 ART 157 SA I ZS N 23 055 lt rr lt gt lt lt ea lt as b ap APPENDIX Temperature Controller The temperature controllers are used to heat and control the temperatures of the reference load amp 5 C and the hot load 65 C The reference load and the hot load are made from a sort of liquid microwave absorbant pound of this absorbant is mixed with 20 milliliters hardener Plaster the mixture onto a 9 0 10 5 cm2 aluminum plate with a mold to dry The surface of the absorber is grooved and coated with a layer of foam which is transparent to the microwave emission The plate is heated by a power resistor controlled by the temperature controller Figure APII A is a schematic of the temperature controller 24 yo NOW 23moo MSZ ef SF g 721 SIL 5 AIE ino ino driv 0 4 IIAT i 99A t N 9 va ann p B 1 Ano AS IMJA 4011 002 WNO 5
19. does not require reading of this manual The manual is mainly written for those who are engaged in construction or maintenance of the receiver system In most cases it is far more difficult to maintain a machine than to operate it This is because there are concepts which are self evident to the builders and designers but may not be so to other persons Some important and useful information can only be obtained by experiencing the process of designing constructing and testing 5 a written description may help to explain some critical points or give some information or clues which are obscure in the schematics With such an intention this manual will not cover every subject but will emphasize the important points However an overall view of the system will be presented 2 GENERAL DESCRIPTION A block diagram of the 225 GHz atmospheric receiver system is shown in Figure 1 rotatable mirror Ml is a section of a parabola with a focal length F 1 2 and a beam width of 4 degrees This beam can be scanned from zenith to horizon with a step angle of 1 8 degrees under the control of computer The beam is chopped at the paraboloid focus by chopper wheel C which switches the beam from the sky signal Ts to reference load signal Tr and to hot load signal Th sequentially The chopped beam is then reflected by a fixed mirror M2 passes lens L and finally enters the feed horn H The local oscillator signal is generated by a commercial 7 5 GHz
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21. pass through the beam they block off the path of sky signal coming from elevation mirror and reflect the thermal emission of the reference load mounted over the chopper wheel or the hot load emission mounted beneath the chopper wheel on alternate blades Between two adjacent blades is a window for transmission of sky signal width of the window should be equal to the width of the blade s projection in the focal plane in order to have equal time periods for the three paths sky reference load and hot load Figure 4 is a photograph of the quasi optical system and Figure 5 is its outline drawing Figure 6 shows the projection of the chopper wheel in the focal plane The distance R shown in Figure 6 from the focus of the mirror to the axis of the copper wheel is 1 61 inches 50 the projection width of the copper blades can be calculated as Fig 4 The Photograph of the Quasi Optical System Reference Load Lens Injection Cavity Fig 5 Outward Appearance of the Quasi Optical System ABSORBER EFFECTIVE REFLECTION AREA ABSORDZR Fig 6 Projection of the Chopper Wheel in the Focal Plane 3 m s rper a L 2 i 125 MIRROR Fig 7 The Mount Angle of the Chopper Blade 25 Sin 22 5 1 232 The angle between the axis of the beam and the normal line N of the blades is not
22. 0 warm up emote Local Sensing Provision included for Ambient Operating Continuous Duty 77766 00 eres EVS F H J improved overall regulation Temperature Full rating O Cto 50 C Protection Built in fold back limiting Short Circuit Protection Automatic electronic circuit Preset Value Overvoltage Protection Built in fixed A P Derate linearly to 50 c of rating at 71 C Storage Temperature i 200 10 85 Quality Control According to MIL 1 45208 APIII C 12V Power Supply Photograph Manufacturer Data Sheets 28 For 82 _ 10 WATTS OF REGULATED 5V 151 OV ISOLATED ANALOG amp DIGITAL GROUNDS 12V OV 12V 5V 931 SERIES POWER U x GENERAL Canton Massachusetts x MEER CONVERTER gt i T n T s SEND BLOCK DIAGRAM SERIES 991 Triple Output 00 02 Converter POSITIVE REGULATOR ere ow ewe E 5 DIGITAL 7 COMMON PO GENERAL DESCRIPTION This new series of 10 Watts Triple Output Converter fea
23. 8 500 300 42 70 255 MIN i 6 3 7 62 d NOTE 3 4 MODEL PIN FUNCTION i i 4 4 INPUT Q 2 INPUT 4 DIMENSIONS SHOWN IN INI 931 3 E OUTPUT p a PTO X XX O C2 x xxx C COS THRU 4 COMMON 24015 pms 040 945 5 Ep OUTPUT 5 702 T TE OUTPUT 4 MOUNTING 5 5 4 40 zT De 7 COMMON 152 witt DRIVE CANTON 02021 TWX 710 348 0200 TELEPHONE 617 828 6216 27 APIII D continued 30 1 2 3 4 5 6 7 APPENDIX IV Connector Wirings Parallel I O Connector Serial I O Connector Connector on the Receiver Component Plate Connector on the Receiver Cover Power Supply and Data Link Connector 11 Receiver to Elevation Mirror Connector J2 Monitor Connector J3 31 APIV A APIV B APIV C APIV D APIV E APIV F APIV G 2 2 23 65 Parallel I O Connector TP TT 296 UN sev 5 OUT ORO APIV B 0020959006060 2000909 In To Socket 3 Serial I O Connector v S v RETURN 5 FoR AMP SYNC H R S R GN D DO OO 00 6 9 49 2 13 9 9 40 eje 6 6 6 9 6 9 9 679 63 6969 69 6 04585 H Tw R 504239 APIV C
24. E VER DooR Top FROM ONTO CONNECT CONNECTOR 53 06 20 295 CONNECTOR CABLE IDENTIFICATION TYPE ASSEMBLER VATE u RR E C MANUAL 5 5 CTR m Z Y R Z ________ mf a MANUAL DIRECTIE Cr 5 2 pd TOLAL POWER ovr 4 or ZD CONTROL STRIGER MILT LINCOLN LABOKA APIV G Monitor Connector 03 36 1 2 3 4 5 6 7 APPENDIX Layout Wiring of the 1 Card The Layout and Wiring of Wire Wrap The Socket Wiring The 5 485 To From RS 232 Link includes chips 2 3 6 7 and 8 The Control Monitor Data Link includes chips 4 and 9 and the VLBA M C card The Elevation Mirror Driver includes chips 12 14 16 19 and 26 The Chopper Wheel Driver includes chips 22 23 24 and 27 Synchronous Controller includes chips 23 25 and 27 30 37 APV A APV B APV C APV D Fig 16 Fig 10 Fig 11 p189 20 pue eup V AdV a ai m s a LM II u 81 4 27205 27 ME 21 me n aiii 122 125 2 4 77 SIVA 27 4 20 6 2 02 ws Z7 d 27
25. LR2 and reset Q2 to zero 7 2 GO ZENITH CONTROL The oscillator 74LS629 supplies 50 Hz clock pulses to gate A When a positive pulse occurs either on the computer controlled CPU GZ line or the manual controlled MAN GZ line it will set the flip flop Ql to HIGH 01 1 which allows the clock pulses pass through gate A and via the Exclusive OR 74LS86 to the motor driver SAA 1027 When the mirror arrives at the zenith position the phototransistor 21 1 sends out a negative pulse This pulse is shaped by the monostable mutivibrator 7415221 and be used to reset the flip flop Ql via the AND gate B therefore closing the gate A and stopping the mirror The other pin of gate B is connected to manual control STEP switch When the MAN ST switch is closed a negative pulse occurs at the output of gate B and resets 01 50 if the mirror is turning on the way to zenith and you push the MAN ST switch the mirror will stop Then each push on the MAN ST switch makes the mirror move one step 1 8 degree 8 INTERFACE AND DATA LINK The data acquisition and monitor control interface are realized by employing a VLBA standard interface card For details please refer to the VLBA specification A55001N002 A 9 CALIBRATION AND RESULT When power supply to the system is turned on and the working program disc is in the computer disc drive the system will setup automatically Normal operation will not occur until the reference load and the hot load are hea
26. NATIONAL RADIO ASTRONOMY OBSERVATORY CHARLOTTESVILLE VIRGINIA ELECTRONICS DIVISION INTERNAL REPORT No 271 225 GHz ATMOSPHERIC RECEIVER USER S MANUAL ZHONG YI LIU AucusT 1987 NUMBER CoPIES 150 10 11 225 ATMOSPHERIC RECEIVER USER S MANUAL Zhong yi Liu TABLE OF CONTENTS Introduction General Description Local Oscillator 3 1 Temperature Coefficient of the Gunn Oscillator 3 2 Tripler Quasi Optical System 4 1 Chopper Wheel 4 2 Lens and Injection Cavity Amplifiers Synchronous Controller Chopper Wheel Driver and Synchronous Detector 6 1 Chopper Wheel Driver 6 2 Synchronous Controller 6 3 Synchronous Detector Elevation Mirror Driver 7 1 Mirror Scanning Direction Control 7 2 Zenith Control Interface Data Link Calibration amd Result Acknowledgements References TABLES Table 1 Tripler Bias and Perforamnce Data Table 2 Mixer and Receiver Parameters Fig Fig Fig Fig Fig Fig FIGURES 1 Block Diagram of the 225 GHz Receiver 2 Comparison of the Temperature Coefficients Between the Original and the Improved Gunn Oscillators 3 Relationship of the Tripler Output Power and Bias Voltage and Pump Power The Photograph of the Quasi Optical System Outward Appearance of the Quasi Optical System Q The Mount Angle of the Chopper Blade m
27. Waveforms of Signals 14 MIRROR Fig 13 Motion of the Blade Switches the Beam from the Sky to the Reference Load and the Square Law Detector Output Waveform 3 5 THE CHOPPER WHEEL BEAM CU T SECTION Fig 14 The Angle of the Beam Cut Section Opened to the Chopper Wheel Shaft 15 blanking pulse for the design of synchronous controller order to determine the pulse width of the blanking pulse it is necessary to determine the time required for the blade edge to pass entirely through the beam Fig 13 The maximum width or the cut section of the beam can be found as L W Sin 1 F 0 269 Where Rl 1 0 equals to the lens radius 1 412 the width of the blade 2 562 the focal length of the mirror 29 27 the angle between the normal line of the blade and the beam axis Referring to Figure 14 we can find how many steps or times it will take for the blade to pass through such a width is equal to the duty Bl of the blanking pulse Bl A 1 8 2 Sin l r R 5 steps 10 mS 6 3 SYNCHRONOUS DETECTOR Figure 15 is a schematic of the synchronous detector The output of the square law detectors fed to the positive input of the OP AMP A inverting input of the OP A is connected to 410 volt DC through a 100 K ohm resistor 5 its output voltage is 10 volts when the input volta
28. andwidth about 0 3 GHZ of the injection cavity the frequency shift of the Gunn oscillator must be less than 0 1 GHz i e the temperature coefficient of the Gunn oscillator must be less than 7 10 0 2 The initial Millitech Gunn oscillators exhibited large temperature coefficients and step changes in frequency as shown in Figure 2 Those were returned to Millitech and much improved units were received The improved Gunn oscillators have a temperature coefficient of about 5 10 C and no frequency step changes were observed The original Gunn oscillators also have large step changes in frequency about 0 5 GHZ when the load impedance was varied but this also was corrected in the new units The output power of the Gunn oscillator should be more than 40 mW in order to provide a sufficient pump power to the tripler 3 2 The tripler is designed at NRAO The theory and constriction were described in papers 2 and 3 The adjustment of the tripler must be performed carefully in order to achieve the best conversion efficiency Because of the highly nonlinear capacitance versus bias voltage law of the Schottky diode adjustment of the DC bias voltage is necessary while tuning the backshorts to find the best bias point Figure 3 gives the relationship of the tripler output power to its bias voltage and pumping power For each bias tad ili b 1111111111 ULL id Eos aspas am
29. ge is zero When the input voltage is Ei its output can be given as 2 Ei 10 000 The output of OP AMP A is fed to three analog switches which are controlled by three synchronous switching signals S R and H respectively So that the sky signal Ts reference signal Tr and hot load signal Th are separately extracted out by those three switches each followed by an integrator The integrators outputs Es Er and Eh are fed to two subtractors to obtain the outputs of R S R and H R that R Er S R 10 Es Er H R 100 Eh Er and Es 2 Grcv Ts Tsys 10 000 mV Eh 2 Grev Th 10 000 mV Er 2 Grev Tr 10 000 mV 16 214 21 e 97 bbr ied ws d yov X a ly M QA wood Mes 4 ye ASI t NIG 8071 1200 5447 L NT 17 Where Grcv the gain of the receiver in millivolts Kelvin 18 primis the observed object s temperature in Kelvin TH passaa the hot load temperature in Kelvin the reference load temperature in Kelvin TSyS 3954 the effective noise temperature of the receiver Then we have 5 20 Grcv Ts Tr H R 200 Grev Th Tr 2 Tr Tsys 10 000 temperatures of Th exactly controlled 65
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31. play system noise temperature of the receiver 1 is less than 1500 K with mixer 23 LO power measured at the output port of the injection cavity is 0 85 mW DC bias is 0 8 volts Diode current is 1 45 mA mixer bias data as well as the resulting system noise temperatures of the four receivers are listed in Table 2 The mixer IF output is fed to the preamplifier which has an 1 to 2 GHz bandwidth 38 dB of gain and 1 1 dB noise figure Miteq Model AFD3 010020 13 amplified IF signal through a filter and a 20 dB attenuator is fed to the post amplifier which has a gain of 40 dB square law detector has a square error of 0 2 7 at an IF bandwidth of 1 GHz 8 10 Fig 9 Injection Cavity s Frequency Features with Different Backshort Settings 11 TABLE 2 and Receiver Parameters Receiver Mixer DC Bias Diode System Noise Number Number Voltage Current Temperature 6 SYNCHRONOUS CONTROLLER CHOPPER WHEEL DRIVER AND SYNCHRONOUS DETECTOR 6 1 CHOPPER WHEEL DRIVER The chopper wheel is driven by a stepper motor 1 8 degree per step The stepper motor driver is an integrated 16 pin dual in line IC type SAA 1027 Figure 10 A 500 Hz pulse train is fed to the motor driver to drive the chopper wheel at 2 5 turns per second sync pulse sent by the phototransistor is shaped by a 74LS221 IC chip and is used to synchronize the synchronous controller and the reference gene
32. pple Current 15mA 40 Max Common Mode Noise Current 5004 A TRANSFER 250 Breakdown Voltage 500VDC Min Isolation Input to output amp E1 E2 to E3 Capacitance 50 pf Resistance 100 Min ENVIRONMENTAL 25 C 71 C Operating Temperature Range 40 C to 125 C Storage Temperature Range MECHANICAL Case Material Module 5 2 56 x 3 00 x 75 automatic restart when the short circuit is removed and input protection against accidental application of reverse voltage polarity Ferrite pot core transformer and 6 sided electrostatic shielding after inherent shielding against ra diated EMI RFI The Analog outputs 15VDC 12VDC are Dual ing and balanced within 0 2 DC DC Converter Photograph Manufacturer Data Sheets 4 0 w w EDC INPUT VOLTAGE E CowPDCDUTPUT ANPUT CURRENT PRICE NOMINALIRANGE VOLTAGE amp CURRENT lt NDLOADIFULLLOAD x D VP NUMBER CAU 5V 4 5V to 5 5V 400 mA 3 7 931 SV 932 55 075 68VDC 933 z15V 165 934 935 SV SV 12 200 5V 1 12 300 50 mA 0 62 60 0 37 5V 100 CASE PIN CONFIGURATIONS 800 20 32 17 7
33. rator 74LS629 6 2 THE SYNCHRONOUS CONTROLLER The synchronous controller as shown in Figure 11 generates the control signals S R and H which switch on and off the synchronous detector s S channel R channel and H channel respectively The three channels extract the sky signal reference signal and the hot load signal from the output of the square law detector So the control signal S and H must keep in synchronism with the chopper wheel In one revolution the chopper wheel switches the beam two times to reference load Tr two times to hot load Th and four times to sky Ts thus each time lasts 25 steps 45 degrees The waveforms are shown in Figure 12 The waveform of the square law detector s output shows that there is a duration of the beam switching i e the beam is not switched instantly The reason is that the beam has a non zero width in the region that the chopper blade cuts as shown in Figure 14 When the blade is at a position between a and a for example it begins to block off the path of the sky signal Ts and to reflect the radiation of the reference load Tr During this period both the Ts and Tr partially come into the mixer The process is similar between the positions b and b but an opposite process Only between the positions a and b does the receiver record the radiation of the reference load Tr Thus the intervals aa and bb must be cut off during synchronous detection That is the purpose of the blanking pul
34. rom the feed horn would reflect off the blades arrive at the absorber and be absorbed entirely absorber is not perfect though somewhat attenuated signal which is still strong enough to affect the bias point of the mixer is reflected off the absorber With a 45 degree blade angle this returned signal travels back to the feed horn and from there to the mixer Choosing some other angle causes the reflected signal to miss the feed horn entirely 0 037 PLATE CHOPPER BLADE Fig 8 The Chopper Blade and Mount Block movement of the relative position will cause a synchronous error and reduce the measurement precision 4 2 LENS AND INJECTION CAVITY The teflon lens is circularly symmetric and has a diameter of 2 inches Its focal length is 1 2 inches surface toward the feed horn is planar and the other side is curved as determined by a set of parametric formulas 4 5 The lens surfaces are concentrically grooved in order to reduce reflection losses The RF signal received by the feed horn is fed to the injection cavity where the RF and the LO signals are combined together The cavity is a resonant device It performs as a bandpass filter for the LO signal The central frequency and the bandwidth are closely dependent upon the tuning of the backshorts see Figure 9 criteria for optimum tuning are as low an insertion loss as possible at the LO frequency and as high a rejection as possible at the sideband
35. s Since a frequency sweeper that works in the range of 220 GHz to 230 GHz was not available the process of tuning the injection cavity was laborious Figure 9 was obtained by using a klystron and a frequency tripler as the signal source The klystron drove the tripler via a variable attenuator and the tripler drove the cavity klystron output frequency was tuned from 74 5 GHz to 75 5 GHz with steps of 0 1 GHz The tripler was retuned and the attenuator was adjusted to maintain a constant output power to the cavity in the frequency range from 223 5 GHz to 226 5 GHz The listed input and output powers of the injection cavity in Figure 9 were measured at 225 GHz with the different backshort settings 5 MIXER AND IF AMPLIFIERS The mixer is a single end device 6 7 RF and LO signals are fed into one port of the mixer GaAs Schottky barrier diode chip is mounted in the reduced height waveguide and is contacted with a gold whisker The mixer tuning is achieved by employing a fixed backshort which is implemented as a section of short circuited waveguide electroformed into a backing plate There are various backshort plates with a range of diode to short spacings available for optimization order to achieve the desired performance the LO power and the DC bias levels should be carefully adjusted when trying backshort plates With each adjustment we can find the changes of the system noise temperature directly from the CRT monitor dis
36. se waveform d in Fig 12 It is necessary to find the width of the 12 Zoo 415 SAA 027 G pe 12 4 2 MOTOR H21A1 4 5 gm pts c 5 12 9 13 7 CLK 7 74151014 4 amp 2 9 0 OIMF 516 uM Fig 10 Chopper Wheel Driver SAA 027 75 Ror 2 3 250 m Clock 2 arm Fig 11 Synchronous Controller 13 is 245 7S MIT ini il M H GA meen ib B 1 i I r ee lt ome me m ay a D 222 212 w w w B Quen on 25 50 75 00 25 50 75 200 waveform of the incident signal chopped chopper wheel b The waveform of the square law detector output Synchronous pulse generated phototransistor d The blanking pulse waveform e f g Synchronous detector switching signals h The driving pulse for the chopper wheel Fig 12
37. ted up and stabilized Check the readings on CRT screen and make sure the REF TEM is 45 C and the HOT TEM is 65 and the H is 20 The system is then ready to operate Normally it will take approximately 20 minutes to warm up depending upon the initial equipment temperature 20 Figure 17 is chart record of the synchronous detector s analog outputs S R and R for different temperature absorbers placed front of the elevation mirror VoL 225 s j sees s mamm oom mee ae a du 8 4 as 5 m quA US ido a O o ip a s s c Eme REYNE m 4 tmm me cum aite a e 1 s we eee 2 20 be I E 2 n woe ome RO SEE EER E wem mee eor ws 1 ome wows owe A pe S Tas n OEM D gt lt s 8 gt s s s s s TRT 2 M n AP ve x cee oe 5 lt o ceo we sew
38. test works were done under his direction and help from beginning to end am grateful to N Horner for his assembly of the mixers and triplers Thanks also go to W Luckado G Taylor and D Dillon for their help with fabricating the many components of the receiver and the measurement systems 11 REFERENCES 1 S Weinreb 225 GHZ Receiver Test Program NRAO Internal Memorandum April 22 1986 2 J W Archer Millimeter Wavelengh Frequency Multipliers IEEE Trans Microwave Theory amp Tech vol MTT 29 no 6 pp 552 557 June 1981 3 J Archer All Solid State Low Noise Receivers for 210 240 GHZ IEEE Trans Microwave Theory amp Tech vol MTT 30 no 8 pp 1247 1252 August 1982 4 J Silver Microwave Antenna Theory and Design 1 Rad Lab Series vol 12 ch 11 New York McGraw Hill 1984 5 Paul F Goldsmith and Ellen L Moore Gaussian Optics Lens Antennas Microwave Journal pp 153 156 July 1984 6 A R Kerr R J Mattauch and J A Grange A New Mixer Design for 140 220 GHZ IEEE Trans Microwave Theory amp Tech no 5 vol MTT 25 pp 399 401 May 1977 7 M T Faber and J W Archer A Very Low Noise Fixed Tuned Mixer for 240 270 GHZ IEEE 5 Int Microwave Symp Dig Pp 311 314 June 1985 8 S Weinreb Square Law Detector Tests NRAO Electronics Division Internal Report No 214 May 1981 22 APPENDIX I Photograph and Schematic of the Square
39. tures isolation between the Analog outputs and the Digital output as recommended by many 0 0 verter manufacturers for the purpose of inhibiting Digital interference in the Analog section and eliminating system ground loop problems models feature internal z input filters to minimize re flected input ripple voltage output current limiting with APIII D 29 GENERAL SPECIFICATION ELECTRICAL INPUT Voltagerange See ordering information Current 5ee ordering information Switching frequency 20 2 OUTPUT Voltage output E1 8 2 1 5VDC 2 1 Balance E1toE2 0 2 Max Tracking 15V and 12V only See ordering information Voltage limiting 0 6 8V Load Regulation NL FL E1 amp 2 0 02 0 1 40 1 0 2 Line Regulation LL HL 2 IDE 0 1 Max E3 0 1 x 0 2 Max Temperature Coefficient 0 02 C Max Initial Warm up Voltage Drift E1 amp E2 x 20mV 90mV gt 10 40mV Current outputs constant current limit protected NOISE Output Noise Voltage All 5 1 mV True RMS Max 15mV p p 40mV p p Max Reflected Input Ri
40. ughout the world User selectable 115 230 VAC dual input ACtransient suppression Overvoltage protection 8 Logic inhibit on many models Overload protection Remote or loca sensing on most models Short circuit protection B Cover included with all models o Parameter Conditions Limits 5 Limits 0 input 47 63 90 132 180 250 Overshoot No voltage spikes on turn on consult factory tor 400 Hz user selectable turm offorpowerfalue L DC Output See Ordering Information Chart Input Surge Current Peak cold start 20 115 PAE SURE nn 4 A DC Output Adjustment 2 10 22 Line Regulation 2 Within specified iimits 0 5 CE Med 2 2 negatwe 4 5105 5 5 0 2 Ia sss 228 Polaritv Either positive negative Up to 300 Noise Ripple DC 50 MHz 75 10 floating m Soft Start Provides input current Hoid uo Time Based upon nominal input 20 ms limiting at turn on 1 8221 Paralle Operation Consult factory Transient Response 50 to 100 load change 2 10 5 Long Term Stabilny gt For 8 hrs after 20 Wa Efficiency According to output voltage 70 8
41. z PLU 22 4 Sdwy 77V No ASL wo yoo 2 7 27 Zs lo Jeo Wo i 2 AWO wor 5 2 2 2 30007 7 gt 1 2 Aw Temperature Controller APII A 25 1 2 2 3 APPENDIX 12 Power Supply DC DC Converter Schematic of the 12V Power Supply Schematic of the DC DC Converter 12V Power Supply Photograph and Manufacturer Data Sheets DC DC Converter Photograph and Manufacturer Data Sheets 26 APIII A APIII B APIII C APIII D 2V BATT APIII A 12V Power Supply CURR SENS I2V CRT Ol 222 12 DC 3319 25 NVERTOR RIAN NVERTER 4 2V RETURN APIII B DC DC Converter 27 2 5 v FOR IF AMPS 50 384 WATT SINGLE OUTPUT owltching Regulated Power Supply Recognized under IEC 380 safety standards Meets VDE 0806 safety design standards Complies with UL 478 and CSA C22 2 154 Input filter conforms to VDE 0871 6 78 and FCC 20780 Part 15 Subpart J The EVS family of single output switchers incorpor ates the latest in switching technology to offer low cost high performance solutions to your power sup ply These efficient light weight units are available in 5 12 15 and 24 VDC versions Units are designed and qualified to meet all of the latest required regu latory specifications used thro
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