PC-Radar User Guide
Contents
1. n txs spline 1l n 1 txdat txdat 1 zz putdata ao txs output chirp data else putdata ao txdat output chirp data end o input sampling rxsig getdata ai n wait for n input samples distance calibration rxsig rxsig shiftindex end 1 shiftindex 1 high pass filter rxh hps filter hp 1 rxsig hps noise blanker st std rxh standard deviation of signal iE clr ent lt 10 mst st clr 0 else mst relax st 1l relax mst simple IIR filter for standard deviation end rxh abs rxh gt 3 mst 0 blank all samples gt 3 standard deviation Hilbert filter rst rxh nd 1 n state of real shift filter shift to baseband w lps filter b a v lps lowpass filter spectrum yr abs sp end mi l end echo of previous transmission if ale ym yd yr actual echo clr 0 else ym relax yd yr l relax ym mean echo end display if mde yy yd yr ym YY yy min yy scl 1 mean yy mxy max yy if scl mxy gt 5 scl 5 mxy end set ls XData 1 2 length ym 2 km_pro_bin modus YData interp scl yy 2 Sdifference else yy ym min ym scl 1 mean yy mxy max yy if scl mxy gt 5 scl 5 mxy end set ls XData 1 2 length ym 2 km_pro_bin modus YData interp scl yy 2 update mean echo end end while run Figure 6 The central signal processing loop of the chirp radar2. signal state of real shift filter o ae sfift to baseband car rxa ae x spectral rotation into baseband lowpass filter x lps filter lp 1 x lps o correlation o distance calibration yd yd shiftindex end 1 shiftindex 1 rotate vector by shiftindex graphic if clr ym relax yd clear mean echo clr 0 else ym relax yd 1 relax ym simple IIR filter end eco ym min ym ecm max eco set lm YData interp eco ecm 2 update graphic of echo o end while run Figure 7 The central signal processing loop of the code radar Legend to Figure 7 The colors of the words mean while key words of the Matlab languge filter standard functions of Matlab including the Signal Processing Toolbox FFT comments Program specific objects and variables are in black They are declared outside of this central loop
3. 03 If this incorrect signal is sent by the incorrect sound output the sound input sees it as a correct signal Samplerate errors of soundcards usually are very large 0 99 1 01 Chirp radar Echo Amplitude over Distance 45h 35p echo signal tb a EN pap IN Pee Mau PE it da 0 5 a 5 10 a 25 25 a E Figure 3 The display of echoes over the distance In this case the sonar application with speaker and microphone as the transmitter and receiver The distances then are scaled by the ratio of speed of sound speed of light The figure shows the author s office Everything beyond 6m is from multiple reflections The display can be controlled by some specific key presses Key Effect c C clears the history of the correlation signals restart of the display h H displays a help text t T toggles the horizontal scale between 1 time delay between transmission and reception 2 backscatter distance in radar application 3 backscatter distance in sonar application air 20 C s S stops the radar application The figures remain on the screen 4 2 Code Radar The code radar transmits a sequence of bits in PSK modulation at 2000 Baud on a carrier of about 1500 Hz The bitsequence is repeated seamlessly The length of the sequence is as large that the period is larger than the propagation delay of backscatter from a long path 2x30000 km The binary pattern is a Ha
4. 5 2 The Code Radar The code radar determines the pathdelay directly in time domain by measuring the time shift between transmitted and received binary pattern The received signal is filtered with the reverse pattern of the transmitted signal as the filter coefficients The absolute value of the filter output is displayed over the time delay or the radar distance or the sonar distance To avoid interference with other stations running PCradar on the same frequency one of the following four Hadamard codes can be chosen code 1 AFA OOH OOCC oO Cont T O00o0od oo ooo O0o00oMdndooO HerL G O O O ret oe O YN 000dTO0ndTo O OH NA O Ooo0on0odoomdo A OO O HA OA 407 0O00O00O00Oo O O Orter qct Odd a 1O00mndoodo Ele eO eA O OG O O 4 EO rt ral St a ot Or E Hiere O ral ra OS Oral eh Mu A OO e o tal oO sh a A dO Sh SI Ost Orr Orte Oo0oood ooo COCO OA TATA oo aa TOCCOA OO 4 N0nAnO0OOOOOoO oo n0d0omiddA Oo n0n7 nT OH oo oo0n0ornoorooo Oo dH41Oo0oooondnoo NnO00O000dn0nordo O OG O O r e A OOA eGA O OO e a na E E E m PEE a R r e E O E E E E aa A Oo AA OA O O ra 4 WOW COCOA THO Cooonr ATA AOA Od Cont T TO0ooodo COOnOOOCOC FC HA OA OTA OCHO Ont A AAA ATH La oo n0doodrd oo N40TTToOoooo HAA On OOOH oo HG OOOO rE e
5. AA Os ah A r St ad AAA TAOTnH OOO A Oo HA OOA TH OCC Oo Coon FW On OFA TAHA o 10 1 5 a OS Ot sth COOTnWOCOOTnA COCOA TAO le a SE e E a E o E e E a ooo Ot st oO A AO O Horn O0O0O00o0dA ll o0O0ddOo0ordoO0rdoo OOG OG OG AWA on AAA O AA OO SES NS on nooo oodnd oo Ont AA O0ooo Oo 91 tA ATA COOCOO FAA Oo A oS ehh eA OOO ah Hoon OFA TDA HOO Ao tO SN E a 00d TO0domn Oo H41O0odoodooo a AM a hi OA Oe Fal OO gt A On OnrA AAO Od TO QOQ OGO C rm Oo HO GOG GOG ret et OO Oo A SD ME AO O Octa Jcr rr OO yT a E an e aa aar EE A T E I E D E AO ia e E Ee E E A a E E E D E E a oo SHA OO rath SA Ni 1O0OO0MdO0ooomdond 00d O00O0mndrTdrdo Ort Q Oaka e ooo a E AE ar A E S E E a O E E E E a e O eO ae A a a C AA AAA OA O O Fo ES a a St Lond AAW TH OCHO O Oost sO TAO AO ot A on on On DATA on Hota ATW OTnW COCOA oO on TH OOCOCO COA Oo On On T o D E E E a O44 EDE A eer V ALAA CA oO A OO AA OA VAR a OA OA OA o HnH41ornoodnoodo O O AO AO aS at gt NA O a O Ar OA OO creaa OOOH YN E e E a E a A a a E E O E O E e E mu E E a E a E COCOA CHO AH CEE O rkr ea O aO OO E s B e SE e E a E OTH A E S a E O E a Hbre O O O O r oooO EEO GO a THON Go AAA aO O OG eT O r O He O c GO e OOO 4 O eae G e O O O Ge joar E e E Ee AE e B E A E S a E OA OO On T E E a AE E E a E T E E 4 O Cr O O Er OO eE a OGO OO er A e T H O GCG OGO r O Oaea Orto 0O ero AG O woa Ere eO G O O O eL ALO O MO AA A Sh O dod TO0odO0omd oo Hon OTH OOOO Oo ve OO SS ral ea St aa al qHFHOOOCCCCC 4 oo T O0odrd To
6. PC Radar User Guide Klaus von der Heide DJSHG 1 General PCradar is a program which in combination with a PC a radio amateur SSB transmitter including the antenna and a corresponding receiver with it s own antenna realizes a simple low bandwidth radar The program is written in Matlab It is compiled by the Matlab Compiler 2 Requirements a To run the program pcsonar exe the Matlab Compiler Rumtime MCR must be installed b pcradar exe runs on all Windows systems later than Win98 and on 32 bit and 64 bit versions c The soundcard must support the samplerate 48000 for chirp radar d Two antennas at sufficient distance such that the direct signal is received not larger than about 60 dB over the noise e Radioamateur SSB transmitter and SSB receiver 3 The Main Window PCradar by DJSHG EJB Radar Type Figure 1 The Main window of PCradar PCradar starts with a simple window which allows selection of the desired experiment Pushing the help button to the right of an option displays specific help 4 The Radar Types PCradar supports two different radar types A mouseclick on the button chirp or code opens the corresponding parameter window 4 1 Chirp Radar This type of radar transmits a tone with raising frequency starting at f and ending at f2 This is a socalled chirp The received signal has a propagation delay proportional to the distance of the reflecting target Therefore the reflected signal has
7. a lower frequency than the actual frequency of the chirp The frequency difference is proportional to the distance ota i Figure 2 The parameter window of Chirp Radar range km The range of the radar can arbitrarily be set low frequency edge Hz The resolution of the chirpradar is proportional to the A difference of both edge frequencies But the edge high frequency edge Hz _ frequencies should not exceed the bandwidth of the SSB transmitter and receiver Therefore the default of 500 Hz and 2500 Hz usually is a good choice in out ratio The relaxation factor controls the time constant of the order 1 IIR filter of the display The integration time is about 0 1 relaxation factor A value 0 1 guarantees a fast display of changes A value 0 001 averages the echoes over about one minute So noise is well suppressed relaxation factor Both radar types need an identical time basis at the sound output and the sound input I e the samplerates in the case of chirp radar 48000 must exactly be the same If these samplerates differ even slightly then the echos move slowly along the distance scale This surely will happen if different soundcards are used for output and input This effect can be compensated by an appropiate value of the in out ratio parameter If for example the output samplerate is larger than the input samplerate the in out ratio 1 003 then the output signal is resampled by the nominal samplerate divided by 1 0
8. damardcode which has minimal autocorrelation Radar Parameters Figure 4 The parameter window of code radar The relaxation factor controls the time constant of the RERET OTE a order 1 IIR filter of the display The integration time is about 0 1 relaxation factor A value 0 1 samplerate guarantees a fast display of changes A value 0 001 HEROE ER averages the echoes over about one minute So noise in out ratio A is well suppressed code number The samplerate may be chosen as 8000 16000 32000 48000 Choose a rate at which the echoes do not move over the distance axis Both radar types need an identical time basis at the sound output and the sound input I e the samplerates must exactly be the same If these samplerate differ even slightly then the echos move slowly along the distance scale This surely will happen if different soundcards are used for output and input This effect can be compensated by an appropiate value of the in out ratio parameter If for example the output samplerate is larger than the input samplerate by the in out ratio 1 003 then the output signal is resampled by the nominal samplerate divided by 1 003 If this incorrect signal is sent by the incorrect sound output the sound input sees it as a correct signal Samplerate errors of soundcards usually are very large 0 99 1 01 If some other station uses PCsonar on the same frequency you can avoid interference by selection of a differen
9. on Hon O rO OGO rI OOO ASA A a A O o ciO OO OO ee Ooo0o0o0odrnooordo Y A OOO FAA AO fo AO O AAA AO OO 90d T10Omnd00rndna A 410 41711701714 A O OA aah O A O lO AiO 241 OCH A an AO shied Cra Owes on dnd O0o0oddTToond Herrie O O O St ht O LD AA OA OO A on T7 nO0omndrdoooo AT OOCTH OH COO oo n0o00o0odrddoodrd oo tOO clear O OGO O On E T E e E a E O E D E E E aa E a Oo Oo000n1rTO0mndrd YN 1O0OOO0OOn dodo NS o ADS Ont ATA OOH OOO th Oo AO at AO St AS Oe O Oost qHondooxnonxne ODO OOGO Oak AAO dO FT Chr OO Ot a HHA OOCOTA COTA COAT O YN 000 077 TO 1 00 00 DO eo e E T HHA OA OA AON sd Sao gt at Orta On a OTA OHOC FO Hoon FAA TT OCHO N M lt Cooononoococd don 1oHOTnWOOO oO NOOO tO DOA on E E E e a e GE a a a E a E o E e 0 AA AO O AA ete 100000 do eh NO Stet ees A e Coot OoOOOCOtAOA oO oes Weds lS O 8 a ond 1 OO r Ao al Oeics SS es while run correction of samplerate error and transmission if abs 1 fsf gt 10 10 zz z fsf cyci 1 10 10 Z zz end fsf cycl txs spline l cycitl txsig txsig 1 zz putdata ao txs output tx signal else putdata ao txsig output tx signal end Q input sampling rxs getdata ai cyci ae wait for cycle input samples downsampling x n ll mi x n a Q H x 0 5 ON ao now samplerate is 8000 Hilbert filter rxi hst filter bh 1 rxs hst rxa rst rxs 1 nd li rxi rst rxs nd 1 cycl ae Hilbert filter analytical
10. onj x t Ad The Chirp Radar Algorithm z xy expli t q expl o t Ad q t At exp i At q A 29 Att Separation of the constant factor a exp i w At qAf and replacement of At by At s c leads to z aexpiQt with Q 2qs c Thus z is a wave of angular velocity Q which is proportional to the length of the propagation path s Therefore the spectrum of z indicates all targets by corresponding peaks The angular velocities of the spectrum only must be mapped to distances by s c Q 2q The Implementation The signal processing loop of the Matlab program directly follows the above algorithm But of course it adds some technical features for a communication with the soundcard b calibration of the timing between input and output c noise reduction by a highpass filter d noise reduction by a pulse blanker e graphical output The main parts of the above algoritm are highlighted in the following signal processing loop of the program by yellow background Legend to Figure 6 The colors of the words mean while key words of the Matlab languge filter standard functions of Matlab including the Signal Processing Toolbox FFT comments Program specific objects and variables are in black They are declared outside of this central loop while run ent cnt 1 correction of samplerate error and transmission if abs 1 fsf gt 10 10 zz z fsf in 1 10 10 Zz zz end fsf
11. t Hadamard code by the parameter code number CDMA technique echo amplitude relative to peak o o 20 25 30 35 sonar distance m Figure 5 The display of echoes over the distance here the sonar application L 1 Ll f f L L ji f L 1 n o 5 10 15 The display can be controlled by some specific key presses Key Effect b B pops up a display with the actual binary code c C clears the history of the correlation signals restart of the display h H displays a help text t T toggles the horizontal scale between 1 time delay between transmission and reception 2 backscatter distance in radar application 3 backscatter distance in sonar application air 20 C s S stops the radar application The figures remain on the screen 5 The Mathematics of the Radar 5 1 The Chirp Radar The Chirp The phase of a constant carrier is a linear function of time t p 0f The phase of a linear chirp is a quadratic function of time t p 01 q The generated complex signal is given by x exp i q The Transmitted and the Received Signal Only the real part of the generated signal x is sent The signal propagates at the speed of light c The length of the propagation path may be s Then the signal is received after a pathdelay of At s c The imaginary part of the received signal is reconstructed from the received real part but with negative sign This complex signal is the complex conjugate of x t Ad y c
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