User Manual
Contents
1. 150 kHz then drops to about 1 dB at 300 kHz and 6 dB at 500 kHz At 135 kHz noise output is about 22 dBc i e relative to sine wave Signal Generator mode Operating Range 0 08 Hz to 400 kHz in any step size with a resolution of 0 08 Hz Power amplifier response drops off below 7 kHz and above 250 kHz 500mW power bandwidth 10 kHz to 200 kHz and depends mostly on the output transformer and coupling network Power Output Amplifier Up to 1W into 50 Ohm load Power level adjustable over more than 60dB range using a DC control Direct Output without power amplifier is 5V p p into 1M Ohm or 1V RMS into 1k Digital Outputs 8 bit sine data to D A converter Generates an 8 bit monotonic analog output 0 5V Four digital outputs PD2 PD5 can be controlled for external use via serial command Power Supply 12V DC to 15V DC at about 150mA Supply need not be regulated Key up 10mA key down up to 150mA Will operate at reduced output down to 7V No standby power required for memory retention Commands Ten immediate mode user or computer commands Serial Interface RS232 TXD and RXD only at 9600 bps no parity eight bit data one stop bit The synthesizer stops while processing commands 11 bytes of EEPROM are used to store the current user settings for power up beacon or normal mode restoration Changes are saved automatically as they are made Physical Can be built on a prototype board about 100 x 75mm and will fit2. in box of similar size Will operate from 0 to 70 C and will tolerate thermal and mismatch overload Micro controller can be programmed and reprogrammed in circuit Modes CW sine wave carrier Noise Pulsed CW Pulsed DC and swept sine wave 71 41RPIINaiea Pitlea and Swaen Ganaratnr ndi Command Summary Axx ADD Add offset of xx resolution steps where xx is 00 to FF Fhhmmll FREQUENCY Set frequency to this value times the resolution The value hhmmll is a 24 bit binary number expressed as six hexadecimal characters 0 to F H HELP Simple help message listing these commands Mn MODE Sets the operating mode where n is a number 0 to 3 0 Sine wave Signal Generator 1 Noise Generator 2 CW Pulse Generator 3 DC Pulse Generator Nhhil NO Sets the pulse mode off time in steps of 21 us hhll represents a value 0 65535 Pp PORT or POWER Sets Port D outputs PD2 PD3 PD4 and PD5 according to the least significant bits of value p These ports can be used with a 4 bit D A to set output power R REPORT Requests a message giving the current settings T TX ON Turns the generator output on Wxx WIDTH Sets sweep step size where xx is 00 to FF in two hexadecimal characters in Frequency Resolution steps x 256 W00 turns off the sweep X TX OFF Turns the generator output off Yhhil YES Sets the pulse mode on time in steps of 21 us hhll represents a value 0 65535 71 41RPIINaiea Pitlea and Swaen Ganara
3. The ZL1BPU Noise Pulse and Sweep Generator User Manual Noise Pulse Generator doc M Greenman 20 09 02 This manual applies to hardware as described in Sweep Generator Schematic doc and firmware SIGGEN2A dated 19 09 02 This document is Copyright M Greenman 2002 Contents Overview Description Signal Generator Sweep generator Noise Generator Pulse Modes Appendix NOORWD 1 Overview The ZL1BPU Noise Pulse and Sweep Generator uses a reduced instruction RISC micro controller to generate sophisticated radio frequency signals using a number of digital signal processing DSP techniques It is very similar in concept to the ZL1BPU LF Exciter almost identical hardware and the ZL1BPU Signal Generator However the features offered are different having both wide band noise and pulse generation capability as well as the sine wave and sweep functions that are so useful The Generator is computer controlled i e it has no conventional front panel controls The operating frequency the sweep pulse and on off commands are all computer controllable using a KISS command protocol only slightly different from the other designs mentioned The only front panel control is the output amplitude control which can also be computer controlled if desired although at a loss of control resolution The Generator has numerous modes and operates over the frequency range from zero to about 400 kHz The outpu
4. alue from 0 to 255 Thus the range is from zero sweep off to 255 x 256 65280 Frequency Resolution steps or 65280 x 0 0794 5187 98 Hz per step Since there are 20 frequencies 19 steps the maximum sweep range is 19 x 5187 98 98571 Hz A list of suitable settings and convenient oscilloscope scales is given in the Appendix A setting of WOO turns off Sweep Generator mode Normal operation on the previous mode may not return unless the Mode command is resent or power is momentarily removed from the Generator 71 41RPIINaiea Pitlea and Swaen Ganaratnr NR 5 Noise Generator Noise Generation mode is entered using the M1 command There are no controls specific to the Noise Generator The peak noise output is the same as the Signal Generator carrier output but of course the energy is spread over a wide frequency range Thus at any single frequency the level appears to be 20 dB or more lower than the carrier Noise is generated using a maximal length pseudo random sequence 24 bits long The sampling rate is 1 2 MHz and so the first null is 1 2 MHz The spectrum of the noise is essentially a squared sin x x response so is approximately flat to about 150 kHz then drops to about 1 dB at 300 kHz and 6dB at 500 kHz The RMS noise voltage can be calculated as follows Vnoise peak amplitude v 2 fetock Volt VHz In our case 2 foigck iS 1 667 x 10 seconds so the square root is 4 08 x 10 root seconds The peak amplitude
5. d by the micro are converted to analog signals by a passive 8 bit digital to analog converter The analog output is buffered and amplified by a 1W audio device with controllable level which is used to provide the high power output The amplifier has a frequency response to at least 250 kHz The RS232 interface consists of a simple transistor design powered by the PC serial port A small 5V regulator powers the micro controller and the unit operates from any 9 15V DC supply typically a 12V SLA or NiCd battery pack or a wall wart style DC supply The current drawn is about 150mA The unit is reverse polarity protected 71 41RPIINaiea Pitlea and Swaen Ganaratnr n2 The Generator has four modes Sine wave CW mode Noise mode Pulsed CW mode Pulsed DC mode In addition there is a sweep generator function used with the sine wave mode This function is set independently of other modes and overrides the other modes There are three outputs e 50 OHM 1W controlled level output 5 250 kHz e FIXED 0 5V output high impedance e SYNC output The 50 OHM output is the main high powered output It is transformer coupled from the power amplifier output and has limited frequency response about 5 KHz to 300 kHz The amplifier is not damaged by open circuit or short circuit but MUST NOT be coupled to an antenna while a transmitter is operating in the vicinity even on another antenna Be aware also that there is sufficient output from t
6. equency Frequency offsets are positive i e will increase the frequency However if the nominal carrier frequency is negative the offset frequency will be less negative This allows negative steps to be generated See the F command for more detail The A command is normally used for computer controlled FSK or sweep generation rather than manual control The value to use can be calculated as follows Value Frequency Offset Hz Frequency Resolution Hz This value is then converted to 8 bit HEX The range is 0 08 Hz to 20 26 Hz 71 41RPIINaiea Pitlea and Swaen Ganaratnr nA FREQUENCY Frequency Set command Syntax Fhhmml This command sets the nominal carrier frequency of the Signal Generator The resolution is one Frequency Resolution step The value hhmmll is six HEX ASCII characters representing a 24 bit number 0 to 16777215 Values that give frequencies much above 400 kHz are not useful in the range F500000 to FC00000 as they exceed the Nyquist Criterion However values from FFFFFFF down to FDFFFFF are useful In this case the phase adder adds a negative value i e the phase steps backwards and a negative frequency is generated In CW Signal generator mode the only effect this has is that the ADD mode A commands subtract rather than add frequency allowing negative steps Setting negative carrier frequencies also allows the Sweep Generator mode to sweep in the reverse down frequency direction The value
7. his amplifier to cause significant interference to other services if the output is coupled to an antenna The amplifier has DC level control and the output is adjustable over greater than 60dB range There is little leakage from the generator and so the output can indeed be reduced to microwatts The FIXED output is direct from the D A converter and while it has no output adjustment it has the merits of being completely flat from DC to in excess of 400 kHz and generates a OV to 5V signal This output will drive about 50mV RMS into 50 Ohm The SYNC output is high when the Signal Generator outputs are on i e when carrier or noise is being generated It is low between pulses in pulse mode and low when pulsed DC is at OV In Sweep Generator mode this output is high only during the first step and so provides a useful oscilloscope synchronizing signal There are two other connectors the RS232 serial port for computer control and the DC power connector The one control knob adjusts the output level of the high power output from about 1W down to microwatts Sine waves are generated very accurately using a 24 bit DDS technique The frequency resolution is 0 08 Hz and the range is 0 08 to 400 kHz The output is 8 bit very clean and free of harmonics and spurious responses The output sample rate is 1 333 MHz Noise is generated using a 24 bit maximal length pseudorandom generator algorithm with four feedback terms A table lookup technique
8. ich define the required setting These commands are covered in detail under the relevant modes and listed in the appendix HELP Provides a list of commands Syntax H The list of commands is given with a terse description of their use and syntax No other action takes place For example H CMDS Axx ADD offset Fhhmmll FREQ set H HELP Mn MODE 0 3 Nhhll NO pulse off Pn PORT R REPORT sts TX ON Wxx WIDTH sweep X TX OFF Yhhll YES pulse on MODE Sets the Generator operating mode Syntax Mn There are four operating modes represented by the value n in the range 0 3 Other values will not be understood The modes are Sine Wave CW Generator Pseudo random Noise Generator Pulsed CW Generator DC Pulse Generator OUN oO Because of the interrupt driven nature of the software this command executes the mode change stores the new mode and then resets the micro controller PORT Sets four general purpose outputs Syntax Pn Four general purpose outputs PD2 PD3 PD4 and PD5 are set by this command The default value of n 0 clears to zero all outputs N can take values from 0 F HEX and the outputs are set bit wise with PD2 being LSB and PD5 MSB It is possible although not implemented in the hardware to use this command to set the carrier output power with a four bit R 2R network connected to the PD2 PD5 outputs and controlling the DC volume control of the amplifier device In this case consider thi
9. is A technique for generating periodic waveforms with high precision and great accuracy Digital Signal Processing Keep it Simple Stupid A term commonly used to describe the simplest peripheral control protocols Low Frequency That part of the electromagnetic spectrum between 30 kHz and 300 kHz Reduced or Rich Instruction Set Controller A type of micro controller which is designed for very fast processing Typically the RISC micro uses a single memory fetch per instruction cycle and frequently just one clock cycle per instruction ni4
10. is easily measured with an oscilloscope being one half the p p measurement The noise received within a given bandwidth can then be calculated For example at 135 kHz with a bandwidth of 13 5 kHz unloaded Q of 10 the noise voltage from a 5V p p noise signal would be 2 5 x 4 08 x 10 0 001 V root Hz Thus in a 2 4 kHz communications bandwidth there would be 001 x V 2400 48 mV noise At this frequency there is no need to compensate for the frequency response of the noise envelope 71 41RPIINaiea Pitlea and Swaen Ganaratnr na 6 Pulse Modes The Pulsed CW mode is entered using the M2 command and the Pulsed DC mode with the M3 command In most respects these two modes are similar except that during the ON phase the Pulsed CW mode generates an RF carrier frequency set by the FREQ command while the Pulsed DC mode generates about 5V DC during the OFF phase the Pulsed CW mode generates an average voltage mid point of the sine wave while the Pulsed DC mode generates about OV DC The Pulsed CW mode always starts with a zero phase carrier but the end of the pulse is not so easily controlled The phase will depend on the relative frequency and on time values With low carrier frequencies or short on times it is possible to generate partial sine waves With care it is possible to adjust the carrier frequency or the on time so that there is an exact number of cycles per pulse The ON and OFF times are set by
11. is used to maximize speed The output is 8 bit with a sample rate of 1 200 MHz so the noise output is Gaussian in response and useful to at least 400 kHz The pulsed CW mode uses the sine wave generator in tandem with a timer which turns on and off the carrier The sine wave always starts at zero phase angle and the off period is at the zero point of the waveform zero sine phase The on and off time are independently controllable in 20 us steps from 20 us to 1 3 seconds The pulsed DC mode is similar to the pulsed CW mode except that the output is 5V when on and OV when off The on and off time are independently controllable in 20 us steps from 20 us to 1 3 seconds The sweep generator uses the CW set frequency as its starting frequency and steps in 20 discrete frequencies in an increasing frequency direction The step size is adjustable over the range 20 Hz to 5 kHz giving a maximum sweep range of up to 100 kHz anywhere within the 71 1RPII Nica Pilea and Swaen Ganaratnr na operating range of the generator Each step has a duration of 2 5 ms so the total sweep time of 50 ms ideally suits an oscilloscope operating at 5 ms division The oscilloscope is triggered from the SYNC output of the generator which is high only during the first frequency step General Commands All the commands to the Generator are in a simple alphabetical format There are 10 single letter commands Some must be followed by hexadecimal values wh
12. rse the sampling rate and the Nyquist Criterion and practical low pass filter limitations set the upper limit of operation at about 1 3 of the sampling rate or about 400 kHz In a DDS system the current phase of the output samples is incremented by a fast adder which adds a phase increment in every sample loop In this equipment the current phase is kept in a 24 bit register and a single 24 bit addition is made during each loop which Thus the smallest phase increment and hence frequency increment is a step of 1 in 2 The sampling rate is of course the loop frequency The actual frequency resolution can then be calculated Frequency Resolution Sampling Rate Adder Resolution or Frequency Resolution 1 333 x 10 2 0 0794728398 Hz This Frequency Resolution sets the basis of all calculations relating to setting the Signal Generator Looked at another way there are about 12 583 discrete frequency steps per Hz A calculator with HEX mode is indispensable for determining the values for the generator commands Sine wave Signal Generator mode is entered using the MO command Generator Commands ADD Add Offset to frequency Syntax Axx This command adds a frequency offset of xx Frequency Resolution steps to the nominal carrier frequency where xx is two HEX ASCII characters representing a value from 0 to 255 The offsets are non cumulative i e issuing a second offset command will add to the nominal frequency not the offset fr
13. s to be the POWER command Otherwise the pins become simple computer controlled outputs 71 41RPIINaiea Pitlea and Swaen Ganaratnr na REPORT Reports settings Syntax R This command causes the micro to issue a one line report of all the current settings For example R M2 A00 Y0010 N0020 WOO PF F030000 The command letter is listed before each value for easy identification The values are in hexadecimal just as they would be entered Hexadecimal commands are used for two reasons first it simplifies the command interpreter software in the Generator micro which has limited program memory space and second it makes control of the device from a computer program easy since the command structure is simple and reliable It is important to note that all commands are issued during a communications interrupt and the signal generator stops generating signals during these events The ON LED also goes out 71 41RPIINaiea Pitlea and Swaen Ganaratnr nA 3 Signal Generator In order to understand how to operate the sine wave signal generator mode it is important first to understand how the micro controller DDS technique works The micro operates a very tight software loop only six instructions nine clock cycles which looks up sine wave values from a table and places the value on a port for D A conversion The micro operates at a clock frequency of 12 MHz so this loop is executed at a rate of 12 9 1 333 MHz This is of cou
14. t is very precise predictable and repeatable The unit is controlled via a simple serial link and is quite inexpensive to build despite its technical performance The settings of the Generator are stored in internal memory so when power is lost the Generator starts up in exactly the same condition when power is restored Although manual operation using a Terminal program on the computer is practical and convenient the commands seem complex and some understanding of the mathematics is required A bespoke computer program can easily alleviate this and provide enhanced performance A spreadsheet DDSCALC XLS is available from the author to simplify these calculations 2 Description The purpose of this piece of precision test equipment is to provide reliable and accurate signals for a range of tests and measurements for Radio Amateur and general electronics audio and LF applications In particular it allows precise and repeatable levelled carrier signals to be generated controlled amounts of noise to be injected antennas antenna tuners and receivers to be swept for correct tuning and performance power amplifiers to be tested using the pulsed CW mode There are probably more applications than the author envisaged simply because the design is so versatile The Generator consists of only three ICs and a handful of other components The main device is an AVR AT90S2313 micro controller which operates at 12 MHz The digital values generate
15. the two pulse commands YES ON and NO OFF NO Sets the duration of the pulse OFF period Syntax Nhhil The off time resolution is 21 333 microseconds and the range is 0 to 65535 times this or about 21 us to about 1 4 sec The value hhll represents a number in this range expressed as four HEX ASCII characters To calculate an off period use the following formula Off or On value period seconds x 46875 1 For example a period of 1 millisecond would be 0 001 x 46875 1 46 to nearest integer or 2E HEX Thus the OFF command would be N002E YES Sets the duration of the pulse ON period Syntax Yhhil The on time resolution and range is identical to the off time and the command calculations are the same The on time and off time can be set completely independently As in the above example an ON time of 1 millisecond would be achieved with the command YOO2E 71 41RPIINaiea Pitlea and Swaen Ganaratnr nin 7 Appendix Specifications Spectral Purity Second harmonic 42 dBc third harmonic 50 dBc no low pass filter All harmonics at least 50 dBc with low pass filter Below 20 kHz all harmonics 60 dBc or better Random spurii better than 60 dBc close in noise below 60 dBc within 1 Hz Sampling rate 1 33 MHz Nyquist frequency 660 kHz Sampling clock and alias image at 1 4 MHz 42 and 54 dBc respectively Noise mode sampling rate 1 2 MHz first null is 1 2 MHz Noise is approximately flat to about
16. tnr ni Frequency Tables Typical carrier or sweep start frequencies and sweep steps for 12 000 MHz crystal operation Frequencies Steps Freq kHz Setting HEX Step size Hz Sweep div Hz Setting HEX 0 F000000 0 0 Wo0 1 F003126 100 200 W04 2 F00624D 125 250 WO6 5 FOOF5C2 200 400 Wo9 10 F01EB85 250 500 WOC 20 FO3D70A 500 1000 W18 50 FO999999 1000 2000 W31 100 F133333 1250 2500 W3D 120 F170A3D 2000 4000 W62 125 F180000 2500 5000 W7A 130 F18F5C2 5000 10kHz WF5 134 2 F19C432 5200 10 4kHz WFF 140 F1AE147 150 F1CCCCC 200 F266666 250 F300000 Sweep Generator Scales The scales below are a useful and convenient way to set up the Sweep Generator Simply print out the scales at a size to match the oscilloscope graticule markings and slip the relevant one at the bottom of the oscilloscope screen Then enter the commands given on the right side of the slip of paper into the Generator eee Se se Se ele Se Se ee Sle ey 100 150kHz 10kHz div F133333 WF5 125 145 kHz 2kHz div F180000 W31 Epe e e Je Je Je e e e 130 140 kHz 1kHz div F18F5C2 W18 125 175 kHz 5kHz div F180000 W7A 150 200 kHz 10kHz div F1CCCCC WF5 E A 0 100kHz 10kHz div F000000 WF5 7I 1RPII Nica Piilea and Swaen Ganaratnr Glossary CW DDS DSP KISS LF RISC 71 41RPIINaiea Pilea and Swaen Ganaratnr Continuous Wave A radio term to describe a constant or keyed single carrier frequency Direct Digital Synthes
17. to use can be calculated as follows Value carrier Frequency Hz Frequency Resolution Hz This value is then converted to 8 bit HEX The useful range is 0 08 Hz to about 400 kHz A value of zero stops the Generator TX ON Start Generator Syntax T TX OFF Stop Generator Syntax xX 71 41RPIINaiea Pitlea and Swaen Ganaratnr n7 4 Sweep Generator The Sweep Generator is not a Mode as such since it overrides other mode settings The Sweep Generator has two simple settings with 20 discrete frequency steps in an up frequency direction although see the note about negative frequencies in Chapter 3 The DDS technique allows incredible frequency flexibility so it is possible to step instantaneously and indeed phase synchronously from one frequency to another Each of the 20 steps has a duration of 2 5 milliseconds so the total sweep time is 50 ms convenient for an oscilloscope set to 5 ms div The sweep speed was chosen as the best compromise between excessive screen flicker and proper sweeping of sharply tuned devices Sweep Commands The sweep step size is set by the WIDTH command and the starting frequency by the FREQUENCY command The Sweep Generator function is entered by setting the W command to a non zero value WIDTH Sets sweep step size Syntax Wxx Sets the frequency increment per sweep step to 256 Frequency Resolution steps per increment in value xx The value xx is two HEX ASCII characters expressing a v
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