XYdisp user manual.
Contents
1. This procedure is a two point calibration assuming a linear log response of the log detector you use ADC value Low High power level Calibrated range ADCvalue a x powerlevel b power level Power level y After calibration the response curve is shown with the correct power level on the Y axis 10 dBm 20 30 h halt r resume l line P pixel b bar cr cal f freq x centre q quit If your log detecor does not provide a power level readout the calibration could still be done if you know at least the power level of the sweeper at one output level setting Most often the maximum output level of the sweeper is specified Connect a reliable attenuator to the sweeper and the log detector to the attenuator output Set the attenuator to a setting that provides a safe high power level to the log detector Calculate the resulting power level and use this level in the calibration procedure Then set the attenuator to provide a low power level to the log detector for example add an attenuation of 60 dB Calculate the resulting low power level and use this level in the calibration procedure Sweeper S Log detector Xout Fout Fin Log out Q Q PC L Attenuator O O Xin Yin a ADC Calibration with an attenuator 3 4 Correct Xaxis labels The cur2. entirely If program appears to work incorrectly you should change the line back to delay 5 Making screen dumps Screen dumps can be useful when you are documenting your work Various programs are available chose PCXDUMP because this program had the option to directly dump an inverted grey scale image of the display to a file It is available on the SIMTEL website at www simtel net search for pcxdmp93 zip 6 The XYdisp program source XYdisp is written in C used this language because of the availability of a free version of Borland s Turbo C www borland com and because started with Peter Anderson s C source of an 12C example of controlling a Philips PCF8574 8 bit I O extender www phanderson com have modified this source to the needs of the PCF9851 ADC DAC used the Turbo C graphics examples to get the plotting part going The source is included with the executable and schematics so you can modify or extend the program to your needs 7 What next Actually you should ask yourself What can do You could extend the program to plot two Y channels instead of one enabling you to do measurements with reflection bridges etc You could add other I2C IC s such as higher resolution ADC s You could try and measure the log detector s input frequency as well resulting in accurate X axis labels The limit to all this is nothing more than your imagination Charlos Potma
3. screened box with suitable connectors for at least the first two ADC channels Although the schematic shows four ADC channels the XYdisp program only uses the X and YO channel See 3 13 where Y2 is also used Decoupling capacitors on the regulator s input and output are important as the 5V DC is also used as the ADC s reference voltage Note that the ADC input voltage must be between 0 and 5 V If your sweeper X and Y output has a different range you should resistive dividers or op amps to bring these voltages into range The ADC is connected to the 12C interface using a short lt 50cm cable Longer cables may result in having to slow down the display rate of XYdisp 3 The XYdisp program 3 1 Program start After starting XYdisp checks the following the display must be at least a VGA type with 640x480 pixels Higher resolution displays will also work but may not look as good due to the pixel interpolation of the display driver If the display is not VGA and has less than 640x480 pixels the program will exit An 12C interface with external power applied should be connected to the parallel port on address 378 LPT1 You cannot change the port setting in this version of XYdisp If the interface test fails the program will report this but will not exit giving you the opportunity to plug in the interface and apply power 3 2 Program initialisation After startup XYdisp will try to open an initialisation file xydisp ini
4. 2002 9 4 Version 1 2 XYdisp user manual 1 Introduction The XYdisp program is a tool for using an old DOS PC or laptop as XY display to show response curves measured by a sweeper log detector combination The sweeper is setup to repeatedly sweep across the frequency band of interest the frequency is applied to the device under test DUT and the DUT s response is measured with a log detector The DUT can be a device such as a filter attenuator or amplifier The log detector converts the input level to a logarithmic DC level across a wide frequency band Suitable log detectors could be the Philips NE604 Motorola MC3356 Analog Devices AD606 or the newer AD83xx variants A typical measurement setup would look like this Sweeper Oscilloscope Log detector Xout Fout Fin Log out Yin Xin O oO oO Oo DUT Sweeper setup using oscilloscope as XY display Using an oscillloscope to display de DUT s response curve is not always convenient More often than not the oscilloscope is already used monitoring some part of the DUT The XYdisp program runs on a simple PC or laptop and thus the oscilloscope is free for other uses Also using a PC to do the display job brings other advantages the PC can make screendumps of the display for documentation purposes the PC can make a dump of the datapoints measured f
5. Interface hardware The interface hardware is in two parts a simple 12C interface connected to the PC s parallel port and a four channel 8 bit ADC controlled through 12C The 12C interface Standard PHILIPS PC parallell port 122 interface ae 5 extern Ci R R R1 R3 R2 R4 m 10k 10k 10k 10k 10k 10k Sarre F4LS05 A C T4LS05 T4L305 we SCL F4LS05 T4L305 SDA FALsos is the standard Philips schematic It uses one 74LS05 a few resistors and a capacitor The power supply is external The SCL SDA and GND leads are wired to a convenient connector The interface could be built on a small piece of perfboard directly soldered to a DB25 connector The ADC schematic is also quite simple gt 9 12 TAILL i EI Mr GND xin Ying To instrument Yin Yin 54 SCL SDA Ta PC I2c iff GND PCFS591 RS R4 R3 R2 Ri 100k 100k 100k 100k 10k It uses one Philips PCF8591 chip This chip has four 0 5V 8 bit ADC s and one 8 bit DAC This version of XYdisp 1 1 uses only the first two ADC channels All channels have a 100k resistor to ground to prevent unconnected inputs adding noise to used inputs Power is supplied externally any 9 12V DC supply will do The SCL SDA and GND leads are wired to a convenient connector The ADC could be built on a small piece of perfboard and mounted in a
6. This file contains a delay no delay option line see 4 and two lines with calibration factors used to display dBm power levels along the Y axis If this file is not present XYdisp will use default values The first time you run the program the calibration values in xydisp ini will result in an Y axis starting at 10 and ending at 260 These values are chosen so that straight 8 bit ADC readings of 0 255 fall in this range After this XYdisp will read the X and Y values and show these on the screen in a line plot 260 h halt 250 r resume 240 1 line 230 p pixel 220 b bar 210 c cal 200 d dunp 190 t title 180 f freq x centre q quit ROBSSSaess Here the Y axis has the default range 10 to 260 and no frequency data or title is shown In the right hand part of the display the menu choices are shown The program shows the response curve of a HF preselector circuit peaked at 5 MHz Note that my sweeper does not have sufficient harmonics suppression the first small peak is caused by he second harmonic when the sweeper is at 2 5 MHz XYdisp works by repeatedly taking samples of the Xin and YOin input in an asynchronous manner This means that XYdisp is not in any way synchronised to the sweeper itself It also means that the display is slowly built up as more and more points along the x axis get measured Althoug display refreshing maybe slow changes in a response curve after tweaking the DUT for example are genera
7. dump the X and Y data points to that file for later analysis in perhaps a spreadsheet program If you have entered frequency data each data point will be output with its calculated frequency otherwise the data points are output as the X number plus the accompanying Y value ale ty 11 992242 68 996209 2 11 992288 68 996209 5 4 11 992333 68 473745 4 11 992379 68 473745 amy 11 992424 68 996209 6 11 992470 68 473745 Loy 11 992515 68 473745 8 11 992561 68 473745 Oriy 11 992606 68 473745 LO 11 992652 67 951282 AML 45 11 992697 68 473745 L2 11 992742 67 951282 ule ae 11 992788 67 951282 14 11 992833 67 951282 If no frequency data has been entered the second column in the data dump file will not be present 3 11 Halt display Option h will halt the display update The X and Y axis are replotted In the left hand corner of the plot the text Stopped appears This option is useful if you want time to study a particular plot or want to make a screen dump 3 12 Resume display Option r will resume the display update 3 13 Suppressing sweeper retrace Sweepers may use a sawtooth shaped sweep voltage with the result that the retrace part of the sweep voltage may be shown in the display 40 dBm 30MHz low pass xYdisp v1 2 o Hae h halt r resunme 10 f l line Pp pixel b bar 20 ec cal d dunmp t title 30 J f freq x centre s sawt s 40 is tr
8. ia s a quit 50 E years Span 33 Centre freq 163 Version 1 2 of Xydisp has been extended with an option s to suppress this part The user must then supply a pulse with a voltage of more than 2 5V to the fourth ADC input Yin2 in the ADC schematic during the retrace part The retrace part will not be shown 10 GBn 30MHz low pass x Ydisp v1 2 0 ji h halt k r resume 10 l line P pixel b bar 20 5 c cal d dump t title 30 4 f freq x centre a s savt s 40 z i tria s azauit 50 J 60 ai ral mn s 70 80 Span 33 Centre freq 163 Option i switches back to normal triangle shaped sweep voltage 3 14 Program end Option q or typing the escape key will end the program 4 I2C and the speed of your PC XYdisp should run on slow 386 as well as on faster 486 PC s The PCF9851 is made for a 100kHz 12C bus speed This means having pulse widths of app 10 microseconds In practice using a short 12C cable pulse widths can be made as small as a few microseconds speeding up the data acquisition quite considerably Timing of the I2C pulses is determined using timing routines that should work independent of the speed of the PC However on slow 386 and 486 PC s these routines will cost too much time to call and therefore the first line in the file xydisp ini with the text delay may be changed in no delay Timing routines are then skipped
9. lly easy to recognise even if the curve is not completely updated 3 3 Calibration The first thing that should now be done is calibration of the Y axis Select option c XYdisp will first ask for a high power level Set the sweeper frequency to the DUT s peak response set the sweeper output level to a sensible value read the actual power level from the log detector output or display and enter this value Let us assume that the sweeper is set to a frequency of 5 0 MHz and an output level of app 0 dBm The log detector would read a little less due to the losses in the preselector let us say 2 5 dBm Enter this value XYdisp will then make a number of Y channel ADC readings and average this value XYdisp will then ask for a low power level Set the sweeper to a frequency well off from the preselector s peak response Let us say the log detector reads 62 dBm Enter this value XYdisp will again make a number of ADC readings and average this value XYdisp will then calculate the regression factors needed to plot the ADC values along a Y axis with dBm labels XYdisp will ask you if you want the calibration values written in the xydisp ini file to be used the next time you start the program The Y axis limits are determined by the high and low power levels you entered Levels are rounded to the nearest multiple of 10 and then an extra 10 is added in both the high and low range In the example above the Y axis limits are set to 10 and 80
10. or further use in a spreadsheet Using a PC the measurement setup would look like Sweeper Log detector O Xout Fout Fin Log out PC DUT O O Xin Yin ADC 12C V f Sweeper setup using XYdisp The disadvantage is that the user has to construct two small pieces of hardware anl2C interface between the PC s parallel port and the ADC Both pieces are however very simple they are described in detail in the following chapter The XYdisp program runs on all PC s that provide the following aparallel port at LPT1 or address 378 DOS 3 0 or better A 640x480 VGA display either colour or monochrome The VGA display is an important restriction The XYdisp program in the current version is not smart enough to deal with different display cards and resolutions This program has been written to be used on old 486 type laptops running DOS It should also run on faster Pentium type PC s but has not been tested on PC s running NT or XP Also note that inputs to the ADC channels should range between 0 and 5V XYdisp works best with sweepers that use a triangle shaped sweep voltage If your sweeper uses a sawtooth shaped sweep voltage the trace where the sweep voltage returns to the start point will also be displayed This may upset the line display see 3 13 2
11. otting the response curve as a bar chart Choose b This gives a more clear display of a response curve with narrow peaks a crystal filter dBm a0 h halt r resume l line o p pixel b bar c cal 10 f d dunp t title f freq 20 f x centre q quit 30 40 50 70 80 n HATTA Note however that XYdisp uses an 8 bit ADC to determine the X value meaning that only 256 different levels are available and that very narrow peaks in the response curve such as in a spectrum analyser display may not be accurately displayed 3 7 Line plot Entering option will get you back to the line plot This is also the default plot mode Line plot may not be the best option if your sweeper uses a sawtooth shaped sweep voltage See 3 13 3 8 Plot title For documentation purposes a title and sub title can be added to the display by choosing the t option The program will ask for a title and sub title string with a maximum of 40 characters 3 9 Frequency data Another option is f This allows you to enter the centre frequency and frequency span The frequency data is displayed along the X axis homebrew 12 MHz xtal filter 10 98m 200171278 vi h halt r resume l line o p pixel b bar c cal 10 d dump t title f freq 20 x centre a quit 30 40 50 60 70 80 Span 0 01 Centre freq 11 997917 3 10 Dump data to file After entering option d XYdisp will ask you for a filename and
12. ve shown in 3 3 is not plotted along the full length of the X axis The reason is that the Xout output of my sweeper has a maximum of app 4 25V This could and should be corrected in the sweeper itself of course but XYdisp has a x option to replot the X axis labels in such a way that they fit the curve This is done after waiting a few sweeps for the curve to be complete and then typing x The program will then determine which X values at the left and right extreme of the ADC range have not been measured and replot the X axis labels accordingly dBn an h halt r resume 1l line o p pixel b bar c cal 10 d dunp t title f freq 20 x centre q quit 30 40 50 60 S on O 70 80 The tick mark at the centre of the X axis is now at the sweeper s centre frequency This frequency is shown on my sweeper s display so always know the frequency at this point 3 5 Pixel plot XYdisp can plot the curve as a scatterplot using pixels only by choosing the p option This was added to slightly speed up the plotting This option should also be used if your sweeper uses a sawtooth shaped sweep voltage The trace where the sweep voltage returns to its start point may be displayed depending on the voltage of the log detector dBn an h halt r resume l line o P pixel b bar c cal 10 d dump t title f freq 20 x centre q quit 30 40 50 60 70 80 3 6 Bar plot Another option is pl
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