1978 , Volume , Issue May-1978
Contents
1. From Refresh Memory Present X Position or Character Generator m 10 oa I d 5 X Shift Control Circuits u 10 u Control Board Rate eia Up Down Sign X To From Multipliers X D to A Converter Intensity Control To Z Axis Circuits Y Position Up Down Sign Fig 5 Simplified block diagram of the vector generator All processing is performed digitally to eliminate drift The coordinates of the instantaneous CRT beam position are held in counters and the counter contents are converted to analog signals for driving the X Y inputs to the CRT display except that the arithmetic units act as pass throughs since the character generator has already computed Ax and Ay Also switching circuits not shown can modify the arithmetic signs and interchange Ax and Ay so the characters can be rotated The character generator is a conventional ROM controlled algorithmic state machine that uses a look up table to find the end points of short vectors for tracing each character Scaling factors can be applied to the algorithms so the character size can be mag nified x1 x2 x4 x8 The Ax Ay coordinate infor mation for each vector end point is sent to the vector generator Refresh Rate The refresh rate depends upon the number of vec tors and characters to be drawn and the number of blanked movements of the CRT beam Each normal size character requires 15 ps to trace The vector trace2. A second method is to step the synthesizer back and forth between two closely spaced frequencies and observe the differences in Counter readings it is then a simple task for the processor to calculate N A frequency measurement is accomplished by the proces sor s multiplying the known synthesizer frequency f by N add ing the result to the frequency fip measured by the counter and displaying the answer f Nf p The harmonic heterodyne converter has the potential to be constructed at a lower cost than the previous two techniques because it can be designed with just one microwave compo nent the sampler and the control decisions and calculations can be performed by a low cost microprocessor Comparison The table below compares the three major down conversion techniques m Freauerey Range TIO WHE peii peak Trenter man 0 25028 1 Fundamentals of Microwave Frequency Counters HP Application Note 200 1 Copr 1949 1998 Hewlett Packard Co tion of the harmonic number N is 2 Cm lt BA where P is the length of the pseudorandom sequence in clock periods Af is the peak frequency deviation of the unknown and Af is the frequency offset be tween the two synthesizers For example if P 215 1 Af 5 MHz and Af 500 kHz max 0 2209 As Fig 5 5342A Counter s FM tolerance is determined by the IF long as max 0 5 N is correctly determined bandwidth w
3. dated If the flag is set it speaks the HP graphics language HPGL to the plotter and the user obtains a raphics hard copy of the graphics information RECEIVER AUDIO TEST 87 67 RF LEVEL DBM 22 Some of the Softcopy Graphics statements are plt x y draw a line to x y scl x x Y v2 establish the scale range ofst x y offset the origin file x designate a file number bfile x x blank these files file x x view these files flsh x y y flash this file x on these monitors y y X X display subsequent data on these monitors bmon x y y blank these files y y from this monitor x vmonx y y view these files on this monitor Because the cartridge tape on which the Softcopy Graphics Library is supplied is written in the Model A s machine language and includes the com call execute the graphics command statements piler there is no need to use the statement to An example of a program written with Softcopy Graphics statements is shown below followed by an explanation of the program steps This program traces the display shown in Fig the result of a radio receiver test and illustrates the relative simplicity of creating graphic displays with the Model 1350A A Desktop Computer as a control ler and the Softcopy Graphics Library using a Model 982 Explanation of the program Line 0 Clears the picture on the CRT screen sets the fixed point format and estab lish
4. mixing with f and counter B accumulates fj pro duced by Nf mixing with f The pseudorandom switching prevents any coherence between the switching rate of the multiplexer and the modulation rate of the FM that might produce an incorrect com putation of N N and the sign of the IF are computed as previously described since counter A accumulates fig and counter B accumulates fip The pseudoran dom sequence is then disabled the main oscillator is selected and the frequency of fip is measured in counter A to the selected resolution The counter s FM tolerance is related to the length of the pseudorandom sequence As shown in the box on page 13 the maximum error in the determina Copr 1949 1998 Hewlett Packard Co Down Conversion Techniques for Microwave Frequency Measurements A frequency counter is limited in its direct counting frequency range by the speed of its logic circuitry Today the state of the art in high speed logic allows the construction of counters with a frequency range of around 500 MHz Continuing advances in IC technology should extend this range beyond 1 GHz in the not too distant future The designer of an automatic microwave counter must look to some form of down conversion to extend frequency measure ment beyond 500 MHz Four techniques are available today to provide this down conversion Prescaling or simply dividing the input frequency with a range of only about 1 5 GHz Heterodyne conver
5. 2 5342A MICROWAVE FREQUENCY COUNTER J HEWLETT PACKARD Ot 2 TOI OL a a a e i O Oe Microprocessor Controlled Harmonic Heterodyne Microwave Counter also Measures Amplitudes The new harmonic heterodyne frequency measuring technique provides wide FM tolerance high sensitivity and automatic amplitude discrimination Simultaneous measurement of input amplitude is optional by Ali Bologlu and Vernon A Barber UTOMATIC MICROWAVE FREQUENCY mea surements to 18 GHz and beyond have generally been done using one of two frequency down conver sion techniques the transfer oscillator or the hetero dyne converter see box page 5 In a new micro wave counter Model 5342A Fig 1 a new down conversion technique called harmonic heterodyne conversion provides many of the advantages of both traditional methods while significantly reducing cost Among these advantages are wide FM tolerance high input sensitivity and automatic amplitude dis crimination The new technique requires only one microwave component a sampler and relies on a microprocessor to perform the required computations thereby eliminating a good deal of digital hardware and its associated expense The microprocessor also adds to the counter s power and versatility by making it pos sibleto manipulate the measured data An easy to use keyboard permits the operator to define frequency offsets or measure frequency deviations An amplitude measurem
6. containing the attenuator under test was made many wavelengths longer than the direct path so while the frequency is swept the microwave power from the two paths at the detector goes rapidly in and out of phase The resulting display on the CRT of the frequency response test set is thus a closely spaced series of peaks as shown in the photo with the envelope of the peaks delineating Frequency Response Test Set Detector Leveling Filter 30 kHz the attenuation vs frequency characteristics of the attenuator under test The advantage of this setup is that the power in the direct path causes the detector to operate as a linear detector as long as the signal from the attenuator path is much smaller than the direct path Much greater measurement sensitivity is thus obtained This system which is used for production line testing of the Model 8496B H Step Attenuators has a dynamic range of 120 dB Much helpful advice was provided by Bob Kirkpatrick in the design of this system Robert Jacobsen Stanford Park Division See Economical Precision Step Attenuators for RF and Microwaves by G R Kirkpatrick and D R Veteran Hewlett Packard Journal May 1974 Hewlett Packard Company 1501 Page Mill Road Palo Alto California 94304 HEWLETT PACKARD JOURNAI Bulk Rate U S Postage Paid Hewlett Packard Company F R To change your address or delete your name from our mailing list ple
7. s now learning piano He s married and lives in San Jose California n SPECIFICATIONS Microwave Frequency Counter HP Model 5342A Input Characteristics Pur FREQUENCY RANGE 100 Mire 18 Gh SENSITIVITY 00 Mha 10124 GMs 28 d m DEDE MAXIMUM UT im vw Onton 002 03 tos pur ev DYNAMIC RANGE 00 Wario 124 Qo 30 68 124 GHW Ole 2508 IMPEDANCE 80 er nominat CONNECTOR Precwon Type emu DAMAGE LEVEL 25 cb OVERLOAD INDICATION Dagia y das when input evet eas 5 38m roma COUPLING de V fac v a arent mera FREQUENCY RANGE 10 He te 90 Me Deve Crus SENSITIVITY 00 10 Ms to 20 Ve 25 ev me 390 f6 He o 25 Wes S0 mV me IMPEDANCE Seectitie MIL 56 pF o S9 norwrat COUPLING me CONNECTOR Type BNC lente MAXIMUM INPUT S00 3 Svr 24 dr or de usa pret 9 ML 200 Ve 50 ve Lr CRYSTAL FREQUENCY 10 Ve STABILITY Agng rte lt 1 10 T per mony OUTPUT FREQUENCY Yo Wee 24V nare wove TTL combi 15V uc DAMAGE LEVEL ze eam RESOLUTION 0 1 a ACCURACY 1 d escudg mami vocem Sun cran MEASUREMENT TOME 100m DISPLAY Sievianeously spins treqvency fa 1 MME resolution and S 10 iy tr Die mm Jor T secre mg me qe me ne OC 0 S7C te v ge hom nomma re tin BO rea Hh rin at 16 POWER REQUIREMENTS 109120220240 Vima 9 10 488 He SQE G3 om 213 e W BB mm D H e EI WEIGHT Na 3 1 bg 20 Seeing 127 g 28 bu PRICES M USA So4pA 4509 Opnons 001 800 092 61000 0nd 375 MANUFACTURING DIVISION SANTA CL
8. the user to diagnose problems to the subassembly level Digital board troubleshooting can be done to the component level using signature analysis see page 8 Front Panel Inputs and Controls The 5342A has two inputs one going from 10 Hz to 520 MHz and the other from 500 MHz to 18 GHz Sensitivity of the microwave input is shown in Fig 12 The right hand side of the front panel deals with input signal channel selection and sample rate con trol of the measurement The left hand side of the front panel enables the user to do data manipulation by keyboard control of the processor Instructions on how to do this are on a label Fig 13 that is affixed to the instrument top The panel layout is in algebraic notation Panel operation closely resembles remote programming via the HP interface bus HP IB When the machine pow ers up it is in the auto mode with 1 Hz resolution As the user selects other resolutions insignificant zeros are truncated Display digits are in groups of three to facilitate reading In case the user wants to bypass the acquisition cycle of the algorithm a manual mode of operation is available In this mode the user should know the unknown frequency within 50 MHz and enter it via the keyboard The counter then acts like a receiver making frequency measurements Offsets can be specified from the front panel Any frequency offset can either be subtracted from or added to the measured frequency In the auto offset m
9. time is according to the list on page 19 and the time for blanked movements is the same as for vector movements As an example consider a presentation that has 50 characters a graticule of 21 vertical and 21 horizontal lines 40 tick marks on the graticule 60 blanked movements to trace the graticule and tick marks 24 blanked movements to position the charac ters and 200 data points joined by short vectors Total trace time is then approximately 50 characters at 15 us 7750 us 42 lines at 48 us 2016 us 40 tick marks at 4 5 us 7180 us 60 short blanked movements at 6 us 360 us 24 blanked movements at 12 us 200 data points at 1 5 us 1 3894 us 250 Hz 20 Hence the refresh rate for this data display is well above the flicker level Processing the Data The data path from the input to the refresh memory is outlined in Fig 6 ASCII coded data written in the graphics translator machine language is accepted through the HP IB interface in the following format NN XXXX yyyy followed by a colon carriage return CR or line feed LF The first two letters NN are a mnemonic for the instruction command see Table I and can be either upper or lower case The parameters xxxx and yyyy are four digit decimal numbers For example the instruction pa 200 500 moves the CRT beam tox 200 y 500 on the 1023 x 1024 matrix pa is the mnemonic for plot absolute xxxx and yyyy may not be used with some i
10. vector end points need to be known the system does not have to take time to calculate intermediate points This speed 1311A Large Screen Display Copr 1949 1998 Hewlett Packard Co To Displays Fig 4 Basic block diagram of the Mode 1350A Graphics Translator The character generator and O module are de signed to be easily replaced if special characters are needed and or if the IIO format needs to be modified enables simulated motion studies How It s Organized The internal organization of the Model 1350A Graphics Translator is shown in the block diagram of Fig 4 The refresh memory contains the data to be displayed It can store up to 2048 vectors and or characters and as mentioned before can be par titioned into 32 files of any length as long as the total file contents do not exceed the memory A separate character generator is included so a complete character can be generated in response to a single ASCII code It is a separate subassembly with its own control circuitry so it can control the instru ment to some extent while drawing characters This enables it to scale or rotate the characters It is im plemented such that the character set can be changed for special applications The I O module for the input and output of data is also a separate subassembly allowing easy modifica tion of the I O format This module was designed almost completely with TTL technology to allow very fast data transfer l
11. 100 MHz Therefore a maximum of 50 MHz peak to peak frequency deviation on the unknown can be tolerated A switch on the rear panel of the 5342A selects either the 20 MHz or the 50 MHz FM mode In the wide FM mode the pseudorandom sequence length is 2096 milliseconds so the acquisition time is significantly increased over the normal mode Counter Design The overall 5342A block diagram is shown in Fig 6 The product design not only decreases assem bly costs but also yields significant RFI performance improvements As can be seen in Fig 7 the entire counter is built into one die casting The boards that constitute the individual assemblies plug into one multilayer motherboard thereby eliminating all Gate Time and PRS Generation Board Counter Board IF Amplifiers and Signal Present Detectors Main Synthesizer and Offset Loop Direct Input Amplifier Line Filter Processor Board A Supply Time Base Amplitude Buffer Option HP iB Board Option Board RF Multiplexer IF Preamplifier Fig 7 Product design minimizes assembly costs and im proves RFI performance A single casting houses all as semblies which plug into a single multilayer motherboard 7 RF Input IF Output IF Output 18 pF 1 8 pF Microstrip Balun Fig 8 Sampler is a thin film hybrid circuit The sampling pulse couples to the slotted line through a balun that gener ates wo opposite p
12. ARA DIVISION 330 Stevens Cree Bouvet Sama Curs Calor 95950 USA Copr 1949 1998 Hewlett Packard Co Generating High Speed CRT Displays from Digital Data Anew graphics translator converts information received from a digital system by way of the HP interface bus into the analog signals needed for tracing vectors and characters on high resolution CRT displays by Arnot L Ellsworth and Kunio Hasebe RAPHICAL DISPLAY of digital data is generally easier to interpret than long columns of num bers Trends curve shapes maxima and minima are much easier to perceive when data is presented in graphical form X Y plotters are widely used for converting digital data to graphics giving accurate permanent records that encompass large amounts of data with fine detail There are times however when a plotter may be too slow In applications that require many plots to be made in getting to the desired result such as adjust ing a circuit fora desired response not only is a lot of paper wasted but the time required to make all those plots may be inordinately long Storage CRTs provide a means of presenting graphical data more quickly than X Y plotters They too can present a great amount of data at one time the amount being limited only by the resolution of the CRT However if only part of the stored display needs to be updated the entire display must be erased and all the data retransmitted to the display Directed beam C
13. In hexadecimal code the four patterns are FF 00 AA and 55 Should a particular location not pass the front panel display shows all E s After the RAM test the 6800 goes through a ROM checksum routine A defective ROM results in a display of 1 2 or 3 on the front panel indicating the failed ROM Successful completion of the above steps causes the instrument to light up all display segments and ront panel LEDs giving the user a visual check The instrument then comes on in the auto mode with 1 Hz resolution and the HP IB interface cleared Keyboard input is connected to the MPU interrupt line When a key is pushed the MPU consults a key table branches to the proper key sequence routine and displays a prompt If the sequence is not com pleted some of the key lights will be kept blinking indicating that the routine is waiting for more key depressions to complete the sequence If an unex pected key is pushed it may be ignored or an error indication may be displayed depending on the situa Frequency ynthesizer 100 kHz Reach 300 MHz Display No Input 0 Detector Output High Add 500 kHz To Synthesizer Frequency Fig 11 5342A sweep flow chart 10 Packard Co Specification Typical 1 31 3151 4 345 TES PE E E 1 2 4 6 8 10 18 1 GHz 12 14 16 Fig 12 Specified and typical 5342A input sensitivity tion Software diagnostic routines are built in as a service aid enabling
14. RT displays on the other hand use a refresh memory any part of which can be up dated without erasing data in the rest of the memory Hence updating is fast enabling a high degree of operator interaction with the digital system Fur thermore refreshed directed beam displays are significantly brighter than storage tube displays Unfortunately there has been a major stumbling block to the use of directed beam displays the need for the user to provide interfacing to the digital sys tem This can be especially troublesome when design and production resources needed for the interfacing are limited A Ready Made Interface The new HP Model 1350A Graphics Translator Fig 1 represents a general solution to the interface problem It accepts data supplied by way of the HP interface bus stores the data and repetitively gener ates the analog signals needed for tracing the speci fied vectors and characters Fig 2 17 All that is necessary to implement a display system with the new graphics translator is to connect its outputs to a directed beam display and its input toan HP IB interface for the system calculator or computer Fig 3 The display needs to have full scale deflec tion factors of one volt and at least 2 MHz response on the X and Y axes and 10 MHz response on the Z axis The system controller may already have an HP IB interface since so many instrumentation systems are now being designed around the HP interface bus Pr
15. When g 1 the local oscillator frequency is set to 1 and fi is gated into counter 1 When g 1 the local os cillator frequency is changed to f and liez is gated into counter 2 At the end of the sequence t T the difference of the num bers accumulated by both counters is used to determine the harmonic number The number M t accumulated by a counter is given by the integral of the frequency during the time the counter is gated on Let M t and M t represent the numbers accumulated by counter 1 and 2 respectively t 3 M t fies dt 4 Tes dt son ta t Me t N fea Udt k Fiea tdt fl Fig 1 We will consider only the upper sideband case The lower sideband case is identical except for a change in sign Let f represent the unknown frequency and N the harmonic number By proper selection of IF amplifier bandwidth and local oscilla tor frequencies we can guarantee that the harmonic and side band will be the same for both oscillator frequencies With that in mind we have fiet f 0 Nf firalt f 0 Nfa Sroa wfjal juo gt nehal T My t Mo t f Q 0f tdt N T fT where T is the length of time for which g 1 and T is the length of time for which g 1 Then DE A ik 9 t at Nete Tif Toto Tih Tato The value of the integral is not available so the second term appears as an error in the calculated harmonic number No For a pseudorandom s
16. anent record of the displayed data The internal 2K word refresh memory of the new graphics translator can be partitioned into 32 files The data displayed from any of these files can be blanked unblanked or erased individually permit ting selective erasure an especially useful feature if standard data is to be retained for comparison with later data Windowing expansion highlighting by blinking selected areas of the display and the use of cursors are also possible The 500 X Y and Z analog outputs can drive several displays in parallel with the same informa tion However four separate blanking outputs are provided so four different blanking signals can be obtained These override the Z axis for the displays Thus information intended only for certain displays in a multiple display set up can be blanked from the others These blanking signals in znal generated 18 effect Compared to the less expensive raster display sys steer the data to the appropriate displays tems directed beam displays have higher resolution because vectors are traced in any direction with con tinuous lines and also because the addressing scheme enables the beam to be positioned with greater preci sion For example the 10 bit addresses used by the new graphics translator permit the beam to be positioned to any of the more than one million posi tions in the 1023 x 1024 point display area Further more updating is faster because only the
17. ase send us your old address label it peels off CHANGE OF ADDRESS katara heat Padard Jorma Va Page MI Rond Pat Alo Cini 8504 USA AION 60 d Copr 1949 1998 Hewlett Packard Co
18. b Bell who helped define the instrument Z Arnot L Ellsworth aay Fresh out of the U S Navy Amie Ellsworth joined HP s Colorado T Springs Division in 1969 as a production line technician He also started engineering studies part time at the University of Col orado In 1972 he transferred to the R and D labs eventually as suming project leadership of the 1317A and 1321A CRT displays before becoming project leader on the 1350A Arnie earned his BSEE degree at UC in 1974 and r his ME degree in 1977 Work and school has left little spare time but weekends are devoted to his family wife boy 5 girl 7 and church work Amie s a Corvette buff and he also joins his daugh ter in learning stunt roller skating Copr 1949 1998 Hewlett Packard Co Laboratory Notebook Swept Frequency Measurements of High Levels of Attenuation at Microwave Frequencies A major difficulty facing anyone measuring high attenuation levels at microwave frequencies is getting adequate power to the measuring instrument s detector One way around this problem is provided by the setup shown in the diagram Microwave power from the sweep oscillator is split off through a series of couplers and supplied directly to the measuring instru ment s detector The remaining power passes through a microwave amplifierand an amplitude modulator then through the attenuator under test before being coupled to the direct power path prior to detection The path
19. cters per line and 51 lines not to exceed memory size at 1 character size 2 PROGRAMMABLE ORIENTATIONS 0 and 90 INPUT CONNECTOR rear panel conforms to IEEE 488 1975 OUTPUT CONNECTORS three rear panel BNC s for X Y and Z axes with shields grounded Four rear panel BNC auxilary outputs for TTL blanking of displays FRONT PANEL INDICATOR LIGHTS power interrupt listen data listen program power on OPERATING ENVIRONMENT TEMPERATURE operating 0 C to 55 C 432 F to 130 F non operat ing 40 C to 70 C 40 F to 158 F HUMIDITY to 95 relative humidity at 40 C 104 F ALTITUDE operating to 4600 m 15 000 ft non operating to 7600 m 25 000 ft SHOCK 30 g level with 11 ms duration and 1 2 sine wave shape VIBRATION vibrated in three planes for 15 min each with 0 25 mm 0 010 in excursion 10 to 55 Hz POWER selectable 100 120 220 or 240 Vac 5 10 6 48 Hz to 440 Hz maximum power 100 VA approximately 80 W Average power dissipation at 60 Hz and 120 V without any options is approximately 74W SIZE 98 mm H x 426 mm W x 511 mm D 3 875 18 937 x 20 125 in WEIGHT 4 5 kg 2 lb PRICE IN U S A Model 1350A Graphics Translator 3450 MANUFACTURING DIVISION COLORADO SPRINGS DIVISION 1900 Garden of the Gods Road P O Box 2197 Colorado Spring Colorado 80901 U S A who provided much help in the development of the Softcopy Graphics Library and to new product plan ning managers Dave Wilson and Bo
20. d are shown in Fig 18 Measurements such as this are made on every unit before installation and the data is stored ina PROM in much the same format as shown in Fig 18 Curve A is stored to eight bit resolution in 0 25 GHz increments and curve B also to eight bit resolution in 4 dB incre ments and every 0 5 GHz The processor uses the frequency and uncorrected amplitude of the input signal to look up the values of correction in each table and to interpolate for intermediate values Since Table B is normalized to the level used in Table A the correction values are simply added together and applied to the result The system that collects the data to calibrate each amplitude module consists of two signal sources and four TWT traveling wave tube amplifiers multi plexed together with attenuators and an output di rectional coupler and power meter under the control of an HP 9825A Desktop Computer via the HP IB This system drives the module under test with all frequencies and amplitudes in its range and with low source SWR and accurately known amplitude The error in the response of the module is then measured and stored in the calibration PROM 15 Amplitude Accuracy Many factors affect the accuracy of an amplitude measurement in the 53424 For traceability of our standards to NBS and their application to individual instruments in production weallow 0 4 dB There can be up to 0 1 dB error in all the digital processes Analog errors s
21. d by PIN diode switches Harmonic A Multip 3enerator Fig 1 Heterodyne converter Transfer Oscillator The transfer oscillator Fig 2 uses the technique of phase locking a low frequency voltage controlled oscillator VCO to the microwave input signal The VCO frequency f can then be measured in a conventional counter and all that remains is to determine the harmonic relationship between that frequency and the input A second VCO is often used to help determine the Sampler Fig 2 Transfer oscillator harmonic member N The counter then measures f multiplies by N usually by extending its gate time and displays the result Harmonic Heterodyne Converter The harmonic heterodyne converter as its name implies is a hybrid of the previous two techniques Fig 2 on page 3 is a simplified diagram of a counter that uses harmonic heterodyne conversion The input f is directed to a sampler with the result ing down converted video signal f f Nf amplified and sent to the counter The sampling frequency f is created by a processor controlled synthesizer The acquisition routine for this down converter consists of tun ing the synthesizer frequency f until the signal detector finds a video signal fi of the appropriate frequency range defined by the bandpass filter Next the harmonic number N must be deter mined as in the transfer oscillator One method of finding N is to use a second sampler loop or similar technique
22. d the sideband must somehow be determined One way to determine the harmonic and sideband is to use two microwave receivers with local oscillators offset by Af The difference between the two IF frequencies is proportional to the harmonic number and the sign of the difference determines the sideband M w At The main disadvantage with this technique is the cost of the two high frequency receivers An alternate solution is to vary the local oscillator frequency for instance switching regularly between two values It can be shown that this technique would be very sensitive to FM pre sent in the microwave signal Another possibility is to apply random modulation to the local oscillator and correlate the applied modulation to the resultant modulation in the IF If there is crosscorrelation between the applied modulation and the FM in the microwave signal there will be an error in the determination of the harmonic number but if this error is less than 0 5 it can be completely eliminated because the harmonic number is an integer In the new 5342A Microwave Frequency Counter a pseudo random signal is used to change the local oscillator fre quency between the values f and f and gate the resultant fier and fie into two low frequency counters This reduces the problem to determining the proper pseudorandom sequence length to give the desired FM tolerance Let g t represent a period of the pseudorandom sequence see Fig 1
23. deo bandwidth and consequent slow response at low levels Point contact diodes are sensitive wideband and have the low origin resistance necessary for driv ing an operational amplifier without biasing but they are not very rugged mechanically and electrically nor are they stable over long periods Planar Schottky diodes have recently been built however with low barrier height so they are usable without bias These Fig 13 Instructions for using the front panel keyboard are attached to each instrument Frequency and amplitude offsets are easily specified 11 Copr 1949 1998 Hewlett Packard Co To Counter Input we Microprocessor Detected RF EE Modulated 100 kHz Fig 14 Planar Schottky diode detectors are used in the op tional amplitude measurement system Two detectors are used to compensate for temperature variations The dc out put voltage V is proportional to the RF sine wave voltage as long as the detectors are matched and is independent of temperature as long as the detectors are at the same tempera ture devices are like point contact diodes but have the stability and ruggedness of ordinary Schottky diodes These diodes are now in use in several HP applica tions They meet all of our requirements except that they are not RMS responding at levels above about 20 dBm Thus we actually measure voltage but make the instrument read out in units of power and it i
24. e Af is the peak deviation of the unknown signal Thus if we want the counter to tolerate 10 MHz peak FM on the input signal and Af 500 kHz P gt 25 600 Since P 2 1 where m is the number of shift register stages in the pseudorandom sequence generator a 15 stage shift register would be needed to generate this sequence References 1 L Peregrino and D W Ricci Phase Noise Measurement Using a High Resolution gs of the 30th Annual Sympo Pro Prentice Luiz Peregrino Luiz Peregrino received the de gree Engenheiro de Eletronica from the Instituto Tecnologico da Aeronautica in Sao Paolo Brazil in 1959 In 1960 he joined HP s mar keting organization for a brief period then spent three years with other companies as a develop ment engineer and field engineer before rejoining HP in 1964 Luiz has been involved in production research and development for many HP products He originated the random modulation concept 4 or harmonic determination used in the 5342A He s a member of IEEE He enjoys skiing and swimming and is a home computer enthusiast Inductors L1 to L3 act as RF chokes at high frequen cies and as part of a 500 MHz high pass filter with the capacitors C1 to C3 at lower frequencies This repre sents an almost lossless method of injecting bias into a broadband planar circuit Detectors CR3 and CR4 as mentioned above are planar low barrier Schottky diodes manufactured by HP They are mounted wit
25. ed a considerable amount of travel in the far east He later be came the intercontinental specialist on the HP interface bus logic analysis and digital signal analysis Wishing to get involved in R and D Kunio transferred to the Colorado Springs Division in 1976 where he did some of the pro gramming and I O design for the 1350A Graphics Translator Kunio was born in Japan but when he was 13 his family moved to Hawaii There he obtained both BSEE and MSEE degrees from the University of Hawaii in 1971 and 1972 Fond of driving Kunio likes to unwind by winding around Colorado s mountain roads in his aging BMW SPECIFICATIONS HP Model 1350A Graphics Translator INPUT INTERFACE HP IS listener only that conforms to IEEE 488 1975 Date acceptance rate is 2 us per character X Y ANALOG OUTPUT 0 2 Vdc to 1 2 V c into 50N X Y analog vectors between addressable pomis Positive up and to the right Z ANALOG OUTPUT 0 10 V unbianked 1 V blanked into 50N ADDRESSABLE RESOLUTION 1090 1000 points MEMORY 2048 Vectors or characters 32 ADDRESSABLE FILES may be of any length that does not exceed memory size Files can be erased or blanked ADDRESSABLE WRITE POINTER allows new data to be written from that address forward CHARACTER GENERATOR 8x12 resolution stroke characters Modified tull ASCII set compatible with HP 9825A keyboard Character strokes are stored in plugin ROM s 4 PROGRAMMABLE SIZES 1x 2x 4x 8x 80 chara
26. ed by Chuck Howey When Chuck 5 GHz 10 GHz B lt e i A Errors at an Input Amplitude of 0 dBm B Deviations from Curve A for Different Amplitudes 15 GHz 20 ae 2GHz 8 0 Input Amplitude dBm Fig 18 Each 53424 amplitude measurement system is cali brated before installation Systematic errors are stored in a PROM and the microprocessor corrects each measurement before display Copr 1949 1998 Hewlett Packard Co opted fora farming career John Shing stepped in and was responsible for digital design and firmware Spe cial thanks are due Al Foster who designed an HP IB interface to the 6800 processor For the amplitude measurement option Steve Upshinsky worked on the low frequency analog circuitry and Art Lange did all the digital work including programming of the calib ration system Thanks also go to Karl Ishoy for help with hybrid circuit production 5342A product de sign was effectively done by Keith Leslie Martin Neil support engineer contributed significantly in trou bleshooting concepts and manual preparation Prod uct introduction was by Craig Artherholt The prod uct was designed and put into production under the Ali Bologlu Ali Bologlu has been with HP for fifteen years and has been project manager for microwave counters Since 1970 He s contributed to the design of many HP frequency synthesizers and microwave counters most recently the 5342A Ali received BS and MS degrees in electr
27. ed onto the side rails The only microwave component required to make the frequency measurements is the sampler Fig 8 This consists of a thin film hybrid mounted in an aluminum package that is manufactured by a hobbing die This technique is similar to coin minting and results in relatively low piece costs Operation of the sampler is similar to that of ing the assembly s outputs for correct signatures documented in the manual it is possible to verify with a high degree of confidence that the assembly is functioning properly If a signa ture is incorrect then signatures are checked back along the signal flow paths from outputs to inputs When a device is found where the output signature is bad but the input signatures are good that device is replaced Reference 1 AY Chan Easy to Use Signature Analyzer Accurately Troubleshoots Complex Logic Circuits Hewlett Packard Journal May 1977 Martin Neil samplers used in previous HP microwave counters On the hybrid are two Schottky diodes placed across a slotted line The sampling pulse couples to the slotted line through a stripline balun that generates two opposite polarity pulses to drive the diodes The down converted signal is taken from two isolated resistors to the preamplifier Resistors across the slot are used to absorb secondary reflections introduced To Rear Panel Connector gt Keybi Fig 9 5342A microprocessor a
28. ent option provides simultane ous measurements of input signal level and input frequency for the first time in a microwave counter Model 5342A measures frequency from 10 Hz to 18 GHz with a resolution of 1 Hz It has an 11 digit display With the amplitude measurement option the user can see input level displayed in dBm with 0 1 dB resolution and 1 5 dB accuracy and frequency can be displayed simultaneously with 1 MHz resolution Harmonic Heterodyne Conversion Fig 2isasimplified block diagram of the harmonic heterodyne technique All of the harmonics of an internal oscillator are simultaneously mixed with the unknown signal by the sampler The output of the sampler consists of sum and difference frequencies produced by each harmonic of the internal oscillator mixing with the unknown The internal oscillator a nUSA 2 programmable frequency synthesizer locked to the counter s time base is incremented in frequency until one of the outputs of the sampler is in the counting range of the low frequency counter The IF detector detects when the IF intermediate frequency is in the range of the low frequency counter and sends a signal that causes the synthesizer control to stop increment ing the frequency of the synthesizer The IF is then counted by the low frequency counter The unknown frequency can be determined from the relation f Nf fg Cover An easy to use key board puts the micropro cessor based Model 5342A Micr
29. equence we have T T T where T is the sequence clock period This difference can be made zero by a small modification of the sequence circuit or it can be disregarded if the sequence is long enough Then we have T T T2 fj f AM _2 M M 2 Ne J df at Let us consider the error term as function of time and take the Fourier transform Using the shifting theorem we have Copr 1949 1998 Hewlett Packard Co hegre F a Es EM CA Upper case letters are used to represent Fourier transforms The term in brackets can be recognized as the Fourier transform of the pseudorandom sequence The term F jw Af can be considered as the input to a linear system and E jw as the out put The transfer function of this system is athe To determine the counter s sensitivity to sine wave modulation present in f t we only need to know H jw This can be easily found at frequencies that are multiples of fy 1 T by taking the square root of the power spectrum for the repetitive se quence E jo H ja mn BN NPH 2l n gt 0 PoUm C77 P H jn2zf 2 where P is the sequence length in clock periods p We can use a safety factor of 2 to take care of the actual value ot H f for frequencies not multiples of fo The worst case occurs for frequencies of the order of fj For large P we have 4 M max A VP a Fig 16 Thin film amplitude measurement assembly 14 wher
30. error codes if all is not well Despite the diagnostic aids provided by the microprocessor placing a microcomputer inside a sophisticated measuring in strument also introduces some serviceability problems After the first prototype was constructed we discovered it was im possible to isolate certain failures to a particular assembly using traditional troubleshooting equipment and techniques Failures involving the microprocessor assembly and the indi vidual assemblies that interface to the microprocessor assem bly were extremely difficult to troubleshoot Even after hours of troubleshooting it was uncertain whether the fault was a control failure originating on the microprocessor assembly an interface failure originating on an assembly s interface with the micro processor or a failure in some other part of the instrument causing the measurement algorithm to hang up or branch to an incorrect program segment We needed a quick way to verify proper operation of the microprocessor control assembly Fortunately there was a solution which even though the instrument had advanced to the prototype stage was inexpen sive to implement and permitted microprocessor verification and fault isolation to the component level This technique called signature analysis relies on a relatively inexpensive trou bleshooting instrument the 5004A Signature Analyzer Signature Analysis Signature analysis as implemented in the 5004A Signature Analyzer em
31. es the size of characters to be used Line 1 Establishes the user s scale range for the plotting area Line 2 Draws the Y axis Line 3 Draws the X axis Writes titles Writes labels on the Y axis tick mark location Writes labels on the X axis tick mark location Reads the DVM measured values and plots data F is a flag that indicates another reading is to be taken 1D 2 D 3D set switches in the test set Lines 4 amp 5 Lines 6 8 Lines 9 10 Lines 11 13 Copr 1949 1998 Hewlett Packard Co Flg 8 Graphics work station uses the Model 1350A Graphics Translator with the Model 9825A Desktop Computer Vectors and characters for all the displays shown here are stored in Model 1350A s files at the same time and directed to individual displays by Model 1350A s blanking signals up to supply the indicated inputs to the DVM Line 14 Stops the program execution Line 15 Sets hard copy flag and continues the program from line 0 Line 17 Beginning of the subroutine to make measurements and to set F 0 if the measurement cycle is complete Acknowledgments Tom Bohley and Bill Mason developed the vector generator Bill also contributed to the character generator and the power supply Mechanical design was by Bill Smith Many thanks are also due Ed Scholtzhauer of the Loveland Instrument Division Kunio Hasebe Kunio Hasebe joined HP s inter continental operations in 1973as a staff engineer a position that in volv
32. h and adds the measured value to the known harmonic tre quency A micropro sor controls the synthesizer and does the computations Fig 1 Model 5342A Microwave Frequency Counter measures fre quencies from 10 Hz to 18 GHz With its amplitude measurement option it can simultaneously mea sure and display frequency and amplitude Keyboard control and mi pro vide ease of operation and data manipulation features synthesizer was stopped fir is known since it is counted by the low frequency counter Still to be de termined are N and the sign of the IF This is done by making one more IF measurement with the syn thesizer frequency offset from its previous value by a known amount Af Thus f f Af This produc an IF fiz that is counted by the low frequency counter The offset Af is much smaller than the IF so if f is less than Nf then fir produced by mixing Nf with f will be greater than fp Conversely if is greater than Nf then fip will be less than fpg This is shown in Fig 3 N is then determined as fir Nf f Nf gt f Nf f amp Nit firs E f NE or if f is greater than Nf fir f Nf Nfy lt f The unknown frequency is then computed as follow Copr 1949 1998 Hewlett Packard Co f Nf fie f f f Nf fier ff Since the frequency of the synthesizer is known to the accuracy of the counter s time base and the IF i
33. h their bypass capacitors on a common metal substrate for close thermal match ing Sincelow SWR is important for an amplitude mea surement careful attention was paid to parasitic reac tances and impedance matching Fig 17 shows typi cal SWR in amplitude mode including the front panel input connector The amplitude measurement circuit is made to serve as an attenuator by biasing PIN diode CR2 with high current and PIN diode CR1 with only about 0 4 mA Most input energy is dissipated in the termi nation R1 and input SWRis low CR1 however looks Copr 1949 1998 Hewlett Packard Co Fig 17 Mode 5342A input SWR in amplitude mode in cluding the front panel connector like about 250 ohms and a small amount of energy approximately 15 dB goes to the sampler This function is controlled by the converted signal level in the IF With this technique dynamic range is in creased to 20 dBm with no danger of overloading the input sampler Amplitude Error Correction A feature of Model 5342A is its ability to correct for known errors according to a stored calibration table before display Since the microprocessor knows the frequency and measured amplitude of the input sig nal it is possible to correct not only for the frequency response of the detector and the insertion loss of the input connector and switch but also for amplitude related errors such as mistracking between detectors Typical errors to be correcte
34. hich is 25 to 125 MHz The IF detector stops the The length of the pseudorandom sequence also sweep when the IF is between 50 and 100 MHz Thus the i allowable FM ls 50 MHz peak to peak affects the counter s measurement time which con Amplitude i Microprocessor podre Sampler Preamplifie IF Limiter Assembly Amplitude i HP IB Module P Assembly Option 011 Amplitude Assembly Option 002 Rear Panel HF Multiplexer PRS Long Offset VCO Main VCO Keyboard Display Amplifier Main Loop Y da Assembly Amplifier Display Driver Fig 6 5342A block diagram Only one microwave component the sampler is needed This helps reduce cost 6 Copr 1949 1998 Hewlett Packard Co sists of three components sweep time N determina tion time and gate time The sweep time is 150 milli seconds or less and the gate time for 1 Hz resolution is one second In normal operation the pseudoran dom sequence length is 360 milliseconds so the total measurement time is about 142 seconds Under these conditions the counter can tolerate 20 MHz peak to peak frequency deviation on the unknown This corresponds to the bandwidth of most tele communications channels The counters maximum FM tolerance is deter mined by the bandwidth of the IF amplifier As Fig 5 shows the allowable range of intermediate frequen cies is 25 to 125 MHz The IF detector is adjusted to stop the sweep when the IF is in the range 50 to
35. ical enginering in 1962 and 1963 from Michigan State University and the degree of Electrical Engineer from Stanford University in 1965 Born in Istan bul Turkey he s married has f three children and now lives in Mountain View California He plays tennis enjoys water sports and coaches a youth soccer team lab management of lan Band and Roger Smith Referenc 1 J Merkelo A dc to 20 GHz Thin Film Signal Sampler for Microwave Instrumentation Hewlett Packard Journal April 1973 2 P A Szente S Adam and R B Riley Low Bar rier Schottky Diode Detectors Microwave Journal M gri 1976 3 R E Pratt Very Low Level Microwave Power Mea surements Hewlett Packard Journal October 1975 4 Fundamentals of RF and Microwave Power Measure ment HP Application Note 64 1 5 D L Slothour Expanded PTFE Dielectrics for Coaxial Cables Plastics Engineering March 1975 Vernon A Barber Al Barber has been designing HP microwave counters for ten years His latest project was the amplitude measurement option for 7 the 5342A Al was born in Chicago and grew up in Fairbanks Alaska He received his BSEE degree from the University of Washington in 1967 and his MSEE from Stanford University in 1970 He s a member of IEEE Al s tastes in recreation run to mountain climbing and classical music He s climbed in the Sierra Nevada the Rocky Mountains the Alaska Range the Alps and the Himalaya and he
36. ig 6 Block diagram of the data processing circuits Copr 1949 1998 Hewlett Packard Co Y coordinate or ASCII character 10 bits File number 5 bits Monitor select code 4 bits Pen control blank or unblank 1 bit File blanking control 1 bit Unassigned 1 bit Pre Programmed Subroutines To simplify the programming of the graphics trans lator a number of graphics utility subroutines for use with several different host computers have been pre pared The graphics command statements in the higher level languages used with these programs were selected to be easy to understand and if possi ble to be already familiar to the user For example one of these routines the 10184A Softcopy Graphics Library designed to run on the Model 9825A Desktop Computer supports the Models 9862A and 9872A Plotters as well as the graphics translator This routine has graphics command statements and parameter meanings for the translator that for the most part are identical to the plotter command state ments Hence the user does not have to learn the graphics translator machine language GTML The hdcpy statement in this subroutine indicates to the desktop computer that the data is to be sent to the plotter for a hard copy output Whenever the user gives a graphics command statement the graphics subroutine first looks for the hdcpy flag If the flag is clear the system speaks GTML to the translator via the HP IB and the CRT display is up
37. in the same instrument In the 5342A lack of ROM space ruled out the software driven implementation To implement the free running approach in the 5342A all that was required was the addition of some switches and pull up resistors to the microprocessor assembly Fig 9 on page 9 shows a block diagram of the 5342A microprocessor assembly The shaded area contains the components added to the assembly to implement free running signature analysis To check out the microprocessor assembly the micro processor is forced into a free run mode by opening the data bus switches S1 this prevents data out of the ROMs from altering the forced free run instruction and grounding the free Copr 1949 1998 Hewlett Packard Co Tun switch S2 When S2 is grounded a clear B instruction is presented to the microprocessor data input clear B was chosen to minimize the number of diodes needed This causes the B accumulator to be cleared and the address to be incremented by 1 Consequently the address lines from the microprocessor repeatedly cycle over the entire address field of the micro processor from 0000 to FFFF By using the most significant address line as both stant and stor for the 5004A and one phase of the microprocessor clock as the 5004A cLocx input repeatable stable signatures are obtained for the microproces sor address lines ROM outputs device select outputs and most circuit nodes on the mictoprocessor assembly By check bolt
38. n cycle is initiated An exception to the above occurs with the plot absolute pa command which causes data to be loaded into memory each time a semicolon ap pears This allows several coordinates to be transmit ted in one statement For example the single state ment pa 100 100 350 900 600 100 100 100 draws a triangle The instruction command tx causes the system to Memory Group em erase memory Auxiliary Display Group wx write auxiliary for display 0 1 2 15 sx stop writing auxiliary for display 0 5 ex erase auxiliary display um unblank memory fl find memory location go into the text mode The 7 bit ASCII code following tx is then loaded into the 10 bit Y coordinate register Character size and angle of rotation fill out the re maining three bits The X coordinate register is filled with 1 s and loaded into memory at the same time as the informmation in Y During readout of the mem ory the ten 1 s in X indicate to the display circuits that the information in Y is to be sent to the character generator Thesystem remains in the text mode until receipt of the end of text character binary 3 Each of the 32 bit words stored in the refresh mem ory contains the following X coordinate or text mode code 10 bits Instruction Command Interface Buffer First and Second Alphanumerics Monitor Ne Program ounter Memory Address Address F
39. ncy fie the counter makes a second measurement with the synthesizer frequency f changed to f f M where Af fie If T Nf then fies fi and if f gt Nf then fipo gt tien as Shown here Then N fe hea 4 G 25 MHz 125 MHz Sampler Driver Pseudorandon quence Synthesize Control Jetector Fig 4 The harmonic heterodyne technique is implemented in the 5342A Counter with two synthesizers and two counters as shown here to prevent frequency modulation on the unknown signal from causing an incorrect computation of the harmonic number N A pseudorandom sequence generator switches between the two synthesizers and the two counters Pseudorandom switching avoids any coherence between the Switching rate and the modulation rate of the FM on the un known The operating algorithm is as follows With the multiplexer having selected the main oscillator out put the main oscillator frequency f is swept from 350 MHz to 300 MHz in 100 kHz steps The offset oscillator frequency f is maintained at f 500 kHz by a phase locked loop When the IF detector indi cates the presence of an IF signal in the range of 50 MHz to 100 MHz the synthesizer stops its sweep and the counter starts the harmonic number N deter mination The pseudorandom sequence output switches between the main oscillator and the offset oscillator and between counter A and counter B so that counter A accumulates fip produced by Nf
40. nning signature analysis has the advantage of not requiring Fig 1 Nine diagnostic modes are available with the counter in Auro mode The set key is pushed twice and is followed by the appropriate digit key ser s r 0 Indicates that the main synthesizer is sweeping SP and that the signal has been placed in the IF 23 and finally that the harmonic determination has been made Ha This display is shown in the photograph 7 Str 1 Displays the main synthesizer frequency the location of the harmonic comb line e g harmonic is below f so must add IF result and the harmonic number N ET 2 Displays results of counter A accumulation dur ing acquisition ser 3 Displays results of counter B accumulation dur ing acquisition 7 4 Displays intermediate frequency being counted 7 SET 5 If Option 002 amplitude measurement is instal led a single corrected amplitude measurement is made and held SET 6 If Option 002 amplitude measurement is instal led a continuous measure of uncorrected amplitude is displayed SET 7 When the signal is removed from the microwave port the main synthesizer sweeps over its full range in 100 kHz steps ET B This mode is a keyboard check any ROM space for storing the stimulus program Software driven signature analysis has the advantage of being able to exercise a greater portion of the instrument s circuitry For thorough testing both techniques could be implemented
41. nstruction commands The system is initialized when the decoder ROM see Fig 6 detects CR LF or a colon The instruc tion counter is then reset to 0 the system is put into the listen program mode and the BCD data shift register is cleared When the system is in this mode the next two alphanumerics received through the in terface buffer are interpreted by the decoder ROM as an instruction If through some error these two al phanumerics are not one of the instruction com mands listed in Table I the system goes into a sleep mode and does nothing until another CR LF or is received After the instruction counter counts the two al phanumerics the system goes into the listen data mode and the numeric data is clocked into the BCD data shift register When a parameter terminator or occurs the register contents are converted to Copr 1949 1998 Hewlett Packard Co Table Graphics Translator Instructions Vector Group pa plot absolute x y File Group nf name file pf blank file uf unblank file sn stop naming file ffi find file en erase file names pe pen 0 up 1 down cs character size and rotation tx text mode binary and transferred through the multiplexers to the register designated by the decoder ROM accord ing to the instruction command When the next CR LF or is detected by the decoder ROM the data is loaded into the next address in memory and a new instructio
42. ode of operation the counter holds the initial mea surement and then displays all succeeding measure ments as deviations about the initial reading Amplitude Measurements Equipped with the amplitude measurement option the 5342A is alone among microwave counters in its ability to make simultaneous amplitude and fre quency measurements Incoming signal amplitude is measured to 0 1 dB resolution with a specified accu racy of 1 5 dB Amplitude offsets can be entered from the front panel in the same way as frequency offsets The most fundamental decision involved in de signing an amplitude measuring system was what element to use to sense amplitude Ideally we wanted a system that is RMS responding from 30 to 20 dBm makes measurements rapidly has stable cali bration is burnout resistant and has low input SWR One choice might have been to use the counter s sam pler and measure its output level Unfortunately this IF level is also a function of the input frequency of the intermediate frequency and of the sampler drive pulse amplitude and frequency and begins to satu rate at about 10 dBm Some sort of switchable at tenuator ahead of the sampler to increase dynamic range would have resulted in an input SWR greater than three at low levels Among other alternatives thermistors are subject to drift and easy burnout and while thermocouples do not suffer these problems their sensitivity is low necessitating a narrow vi
43. ogramming is straightforward Vectors are traced by specifying the coordinates of the vector end points Characters are drawn by specifying each character by a single ASCII code lower or upper case and the starting position of the character string Fast Results The principal advantage of using the new graphics Hewlet Packard s implementation of IEEE standard 488 1975 ANSI Standard MC 1 1 and BUS CEL Fig 1 The new Model 1350A Graphics Translator converts outputs from digital systems to analog outputs for driving high resolution directed beam CRT displays It will be particu larly useful for systems involving engineering design statis tics medicine process control radar and any others requir ing high resolution graphics display Copr 1949 1998 Hewlett Packard Co Instrumentation translator and a directed beam display is the in creased system throughput rate Where changes are being made in the data to be displayed the effects of changes are immediately apparent Curve fitting for example can be done much more quickly than with other display devices When the system user has to make decisions related to scale factors data limits and so on the interactivity and speed of response of the graphic display system shorten the time needed to configure the display parameters so the data is pre sented in the optimum form Once the data presenta tion is optimized an X Y plotter connected to the HP IB can give a perm
44. olarity pulses to drive the Schottky diodes wiring except for the rear panel power connections The power supply is of the switching regulator type The power supply boards are also inside the casting but in a separate compartment so the switch ing spikes are contained and are not permitted to in terfere with the rest of the circuitry On the front panel a fine metallic mesh covers the LED display and attenuates emissions from this area These pre cautions have resulted in improved RFI performance with respect to past instruments The casting is also the main structural element of the instrument The side rails of the box are attached to it and the front and rear panel assemblies are Copr 1949 1998 Hewlett Packard Co Signature Analysis in the 5342A Incorporating microprocessor control into the 5342A Mi crowave Frequency Counter made it possible to develop a powerful measuring instrument at a substantial reduction in cost Besides providing many operational benefits such as keyboard entry of frequency and amplitude offsets resolution selection and offset recall microprocessor control enhances the serviceability of the 5342A by providing powerful diagnostic routines also selectable from the front pane keyboard that aid the service person in fault isolation and instrument verification see Fig 1 Other microprocessor routines exercised every time the instrument is turned on check the health of ROMs and RAM and display
45. owave Frequency Count er through its paces This new counter measures fre quencies and optionally amplitudes with or without offsets up to 18 GHz and has extensive built in self test facilities In this Issue Microprocessor Controlled Harmonic Heterodyne Microwave Counter also Measures Amplitudes by Ali Bologlu and Vernon A Barber page 2 FM tor Deter deband by A Technique that Is Insensiti mining Harmonic Number a Luiz Peregrino page 13 Generating High Speed CRT Displays from Digital Data by Arnot L Ellsworth and Kunio Hasebe page 17 Laboratory Notebook page 24 Swept Frequency Measurements of High Levels of Attenuation at Microwave Frequencies d Company 1978 Copr 1949 1998 Hewlett Packard Co where f unknown frequency N harmonic of frequency synth B f programmed frequency of synthe sizer fj IF produced by Nf mixing with fy fj of the programmable synthesizer is it is known where the indexing of the The frequenc known since Low Frequency unter Sampler Sampler Driver Programmable Frequency Synthesizer Synthesizer Control Fig 2 Simplified block diagram of the harmonic heterodyne frequency conversion technique used in the 5342A Counter All harmonies of a frequency synthesizer are simultaneously mixed with the unknown in a sampler The synthesizer fre quency is incremented until one of t puts is in the output determines w
46. plifier ahead of the analog to digital converter This combination allows better than 0 03 dB resolu tion at all levels and avoids the drift problems of a log amplifier Once the processor has logged and scaled the result it uses the frequency information obtained in a previous measurement to correct the result according to a calibration table stored in memory more about this later Thin Film Hybrid All of the microwave components are contained in a thin film assembly Figs 15 and 16 The dc block ing capacitors and all resistors are integrated on two sapphire substrates one for the microwave detector CR3 and the other for the low frequency detector CR4 CR1 and CR2 are PIN diodes used to route the input signal either to the counter or to the detector Modulated 100 kHz 12 Fig 15 All of the microwave components of the amplitude measurement system are con tained in a thin film assembly De tectors CR3 and CR4 are planar low barrier Schottky diodes man ufactured by HP Copr 1949 1998 Hewlett Packard Co A Technique that Is Insensitive to FM for Determining Harmonic Number and Sideband by Luiz Peregrino The basic principle of a heterodyne microwave counter is the use of a sampler or harmonic mixer to convert the high frequency signal to a low intermediate frequency IF that can be counted directly Before the frequency of the microwave signal can be computed from the measured IF the harmonic number an
47. ploys a data compression technique to reduce long complex data streams at circuit nodes to four digit hexadecimal signatures By taking the signature of a suspected circuit node and comparing it to the correct signature which is empirically determined and documented in the operating and service manual proper circuit operation is quickly verified By probing designated nodes observing good and bad signa tures and then tracing back along the signal flow from outputs to inputs the cause of an incorrect signature may be discovered and corrected In operation four signals must be supplied to the signature analyzer A stant signal initiates the measurement window Dur ing this time window pata from a circuit node is clocked into the signature analyzer A cLock signal synchronizes the data Astor signal terminates the measurement window There are two ways to implement signature analysis and meet the requirements just mentioned in a microprocessor based product free running and software driven In the free running method the microprocessor is forced into an operating mode in which it cycles continuously through its entire address field START STOP signals are derived from the address bus lines In software driven signature analysis a stimulus program is stored in ROM The stimulus program generates stantsto signals and can also write repeatable DATA streams onto the data bus for testing other assemblies connected to the microprocessor Free ru
48. s accurate as long as the signal does not contain much amplitude modulation The diode output voltage is a function of tempera ture and must be compensated The circuit that does this see Fig 14 also provides another advantage For A sufficiently large V4 V4 Since the detector out puts are equal their inputs must be equal if the detec Bias Detected RF To ies C2 Detected uF tors are identical and their outputs are independent of frequency Therefore Var V2 KVg Thus Vo the dc output voltage is proportional to the RF sine wave voltage regardless of the transfer func tion of the detectors as long as the detectors are matched The output is also independent of tempera ture if the diodes are at the same temperature The detector output voltage at 30 dBm input is about 0 5 mV so the dc characteristics of the differen tial amplifier are very important The amplifier is a hybrid laser trimmed for low offset voltage and drift The low origin resistance of the detector diodes allows the amplifier bias current to be drawn through the reverse direction of the diodes without introducing appreciable offset To display amplitude in dBm we need the loga rithm of V The availability of monolithic integrating converters of 13 bit accuracy allows this function to be performed by the instrument s microprocessor instead of the usual logarithmic amplifier The dynamic range is further increased by a switchable de am
49. s mea sured to the accuracy of the counter s time base the accuracy of the microwave measurement is deter mined by the time base error and the 1 count error inherent in any counter Automatic Amplitude Discrimination The bandwidth and gain characteristics of the IF provide automatic amplitude discrimination This means that the counter will measure the frequency of the highest level signal in the presence of a multitude of signals at different frequencies provided that the desired signal is larger than any other by a certain minimum number of dB The specified minimum separation for the 5342A is 6 dB for signals within 500 MHz of the desired signal and 20 dB for signals farther away Typical values are lower FM Considerations The discussion up to now has dealt with the ideal case in which the counter is measuring input signals with little or no FM However many signals in the microwave region particularly those from micro wave radios have significant modulation on them To prevent this modulation from causing incorrect computation of the harmonic number N the har monic heterodyne technique is implemented as shown in Fig 4 There are two synthesizers offset by precisely 500 kHz two counters and a pseudo random sequence generator that controls a multi plexer and the two counters synchronously Fig 3 To determine the number N of the synthesizer har monic that produced the sampler output at intermediate fre que
50. ssembly Components in the shaded area were added for troubleshooting by signature analysis Only a few switches and pull up resistors were required 9 Copr 1949 1998 Hewlett Packard Co by the sampling pulse Microprocessor Architecture Measurement control and system coordination of the 5342A are implemented by a 6800 microproces sor The microprocessing unit MPU handles inter facing to the analog circuits the power up routine display control keyboard manipulation and control frequency and amplitude measurements arithmetic calculations and diagnostics Figs 9 10 11 The MPU consists of one 6800 chip 128 bytes of RAM random access memory and three 2K byte ROMs read only memories that store the MPU programs Decoder drivers for peripheral circuit interfaces and diagnostic switches to facilitate signature analysis for trouble shooting are also located on the processor board A ribbon cable transports the address data Display o Check IF Auto Mode Compute f N Set Synthesizer tot Find Correct f Do PRS Find N Display Measured Result Measure IF Manual or Low Range Mode Fig 10 Simplified 5342A system flow chart Copr 1949 1998 Hewlett f and necessary control lines to the rear panel for inter facing to external devices During the power on cycle the 6800 first does a RAM exercise by doing a READ WRITE for each memory location using four different patterns
51. t 2 ys character or 20ys point Much of the TTL circuitry could have been replaced with a less expensive microprocessor system but this would have slowed the data transfer rate signifi cantly Vector Generation Among other requirements there is an important one that the design of the vector generator had to meet the CRT beam should be moved at the same constant rate for all vectors regardless of length and 18 angle so the beam intensity will be uniform everywhere on the display This is difficult to do at the speeds required for a refreshed directed beam display Consequently the vector generator approximates the ideal situation by using one of six tracing times and one of 32 intensity levels for each vector according to its length This gives 6 x 32 192 combinations of tracing times and intensity levels to approximate the ideal constant tracing rate A block diagram of the vector generator is shown in Fig 5 To assure long term stability digital techniques are used right up to the line driver amplifiers This has resulted in very good tempera ture stability as well as good demonstrated reliabil ity Operation is as follows The coordinates for the next vector endpoints are latched in the NEXT X Y latches When the system finishes tracing the present vector the arithmetic units subtract the present X Y position coordinates from the next position coordi nates The results are the Ax and Ay components of the next
52. ter allowing measurements as high as 20 GHz Transfer oscillator used in counters with ranges to 23 GHz Harmonic heterodyne converter a new technique that can provide measurements to 40 GHz and is used in the new Model 5342A Microwave Frequency Counter to measure up to 18 GHz Heterodyne Converter In a heterodyne converter the incoming microwave signal is mixed with a high stability local oscillator signal of known fre quency resulting in a difference frequency within the range of a conventional counter see Fig 1 The high stability local oscil lator signal is generated by first digitally multiplying the fre quency of the instrument s time base to a convenient fundamen tal frequency fin typically 100 to 500 MHz This fin is directed to a harmonic generator that produces a comb line of frequencies spaced at fin extending to the full frequency range of the counter One line of this comb Kf is then selected by a mi crowave filler and directed to the mixer Emerging from the mixer is an intermediate frequency equal to f Kf This fre quency is amplified and sent to the counter The display con tains the sum of the intermediate frequency and Kfiy In practice the system begins with K 1 and steps the mi crowave filter through the comb line until a detector indicates that an intermediate frequency in the proper range is present The microwave filter may be a YIG filter or an array of thin film filters that are selecte
53. uch as op amp offset modulator linearity noise and A to D converter accuracy can add a maximum of 0 3 dB While drift with tempera ture is typically less than 0 2 dB from 0 to 50 C we allow a maximum of 0 4 dB The worst case uncer tainty for all these variables together is thus 1 2 dB These errors although not random are independent and will rarely add to this value The root sum of the squares uncertainty a more realistic value of ex pected error is less than 0 6 dB To this value must be added mismatch uncertainty which depends upon the SWR of both the source and load Reference 4 contains a good discussion of this Low loss cables are recommended for routing sig nals to the front panel of the 5342A Flexible cable with repeatable insertion loss less than semi rigid coax has recently become available and is very con venient to use Acknowledgments Many individuals made significant contributions to the 5342A The single sampler concept was first suggested by John Dukes Tom Coates provided mi croprocessor support software and other user aids that got the project off to a running start The sampler was the result of Jeff Wolfington s ingenious efforts The power supply was done by John Gliever We were fortunate to have Yoh Narimatsu working on the synthesizers Art Bloedorn did the IF preamps and the direct input channel and also took production en gineering responsibility for the product Digital de sign was initiat
54. vector The Ax component is right shifted until a com parator indicates that the five left most bit positions are filled with zeros The number of shifts required is a gross indication of the length of the Ax component The same operation occurs with the Ay component and the control circuits then select the larger of the two shifts as the designator of tracing time Vector length determines tracing time as follows Tracing Vector length time 1 gt length gt 1 2 of full screen 748 us 12 gt length gt 1 4 24 us 14 length gt 1 8 12 us 1 8 gt length gt 1 16 6 us 1 16 gt length gt 1 32 3 us 1 32 gt length gt 0 71 5 us The upper four bits of Ax and Ay are summed to obtain a five bit number for control of the intensity level The shifted Ax and Ay components are applied to rate multipliers that divide down the input clock rate according to the magnitudes of Ax and Ay The divided down clocks increment or decrement the X and Y position counters and the D to A converters generate analog signals proportional to the counters instantaneous contents moving the CRT beam through a series of microsteps to arrive at the next position three pole low pass filters in the drive amplifiers smooth the microstep transitions When thecontrol circuits determine that the correct number of clocks have occurred the rate multipliers are stopped Operation with the character generator is similar Copr 1949 1998 Hewlett Packard Co
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