Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt, E. Rubiola, C. Eustache
VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
February 4, 2017
1 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
Why ? Only when certain events recur in accordance with rules or regularities, as is the case with repeatable experiments, can our observations be tested – in principle – by anyone. We do not take even our own observations quite seriously, or accept them as scientific observations, until we have repeated and tested them. Only by such repetitions can we convince ourselves that we are not dealing with a mere isolated “coincidence”, but with events which, on account of their regularity and reproducibility, are in principle inter-subjectively testable.
K. Popper, The Logic of Scientific Discovery, (1935) p.23
2 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ?
Why ? Only when certain events recur in accordance with rules or regularities, as is the case with repeatable experiments, can our observations be tested – in principle – by anyone. We do not take even our own observations quite seriously, or accept them as scientific observations, until we have repeated and tested them. Only by such repetitions can we convince ourselves that we are not dealing with a mere isolated “coincidence”, but with events which, on account of their regularity and reproducibility, are in principle inter-subjectively testable.
Conclusion References
K. Popper, The Logic of Scientific Discovery, (1935) p.23
An open-source GNSS software receiver allows to have full access to the signal processing and to make add-ons to the source code in order to obtain the desired GNSS reflectometry processing. L. Lestarquit & al., Reflectometry With an Open-Source Software GNSS Receiver: Use Case With Carrier Phase Altimetry, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2016)
3 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
DCF-77 modulation schemes Radiofrequency wave s(t) = A(t) · cos(ω · t + ϕ(t)) ⇒ carrier frequency (Cs, from PTB), amplitude (1 s), phase modulation
J.-M Friedt & al.
Modulation and Coding Pseudo random noise phase shift keying of the carrier
Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
Carrier, amplitude modulation and PRN are phase synchronous. Phase deviation ± 14.3° Chiprate 645.83 cps corresponding to 1.55 ms per chip
EFTS 2016 TT-2 A. Bauch
41
Can we use this information to measure the delay between air (bouncing off the ionosphere) and surface waves ? 0 A.
Bauch, Time Dissemination II, EFTS2016
4 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Ionosphere altitude
J.-M Friedt & al. Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
J.S. Belrose, The oblique reflecion of CW low-frequency radio waves from the ionosphere, in W.T. Blackband, Propagation of Radio Waves at Frequencies below 300 kc/s (1964), chapter 11. 0 Sudden Ionospheric Disturbances (SID) monitoring station at http://sidstation.loudet.org/data-en.xhtml 5 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ?
DCF-77 • 50 kW emitter in
Mainflingen, Germany, 370 km from Besan¸con • Carrier referenced to Cs
primary standard (PTB) • used to synchronize
radiofrequency-disciplined clocks
Conclusion
• 77.5 kHz: surface wave and
References
air wave bouncing off the ionosphere
0 A. Bauch, P. Hetzel & D. Piester, Time and Frequency Dissemination with DCF77: From 1959 to 2009 and beyond, PTB Mitteilungen 119 (3), 2009 6 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
DCF-77 • 50 kW emitter in
GPS
Mainflingen, Germany, 370 km from Besan¸con
1575.42 MHz km
J.-M Friedt & al.
• Carrier referenced to Cs
20000
Introductions VLF reception
primary standard (PTB)
ionosphere F−layer (300 km)
AM v.s PM
• used to synchronize
Sound card SDR
ionosphere D−layer (50−90 km)
DVB-T: sampling resolution ?
1 41
Conclusion
ground/air ∆τ∼100 µs
Me
370 km
3k
m
km
38
References
day/night ∆τ=95 µ s 77.5 kHz
DCF−77
radiofrequency-disciplined clocks
• 77.5 kHz: surface wave and
air wave bouncing off the ionosphere
1: catm = c0 /1.000338 2: cgnd < cair : 0.5 µs @ 370 km 0 C. Hargreaves, ASF Measurement and Processing Techniques, to allow Harbour Navigation at High Accuracy with eLoran, MSc Univ. of Nottingham (2010) 7 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al.
Short antenna impedance and quality factor Coil + parallel capacitance for tuning antiresonance at operating frequency: V = 2π A·N·Eλ·cos(ϑ) × Q
Introductions VLF reception
10/24/2016 3:16:58 PM 1311.6004K12-101582-pP
Trc3
AM v.s PM
Z11 Lin Mag 5 kΩ/ Ref 10 kΩ Cal
1
35000 30000
M4 M1
25000
Sound card SDR
20000 15000
DVB-T: sampling resolution ?
M3
M2
10000 10 kΩ 5000 0
Bandpass Ref to Max Track Bandwidth 1.902000kHz Center 77.836191kHz Lower Edge 76.891000kHz Upper Edge 78.793000kHz Quality Factor (3dB) -----Quality Factor (BW) -----Loss -21751.4718dB M1 77.873000kHz 21.234kΩ M2 76.891000kHz 10.669kΩ M3 78.793000kHz 10.860kΩ M4 77.836000kHz 21.455kΩ
-5000
Conclusion
-10000 -15000
References
Ch2 Center 77.5 kHz Trc4
Pwr 0 dBm Bw 1 kHz
Span 20 kHz
Z11 Phase 20°/ Ref 0°Cal
2
100
M2 87.487000kHz -87.86° M3 78.784000kHz -60.82° M4 77.823000kHz -0.30 °
80 60 40 20
0°0
M4
-20 -40
M3
-60
M2
-80 -100
Ch2 Center 77.5 kHz
Pwr 0 dBm Bw 1 kHz
Span 20 kHz
Z11 indoor ⇒ need to locate the antenna outdoor to get rid of lab-generated noise ⇒ need to introduce impedance converting circuit (antiresonance = maximize voltage with no current flow) + prevent Q degradation 8 / 32 (http://www.qsl.net/dl4yhf/dcf77_osc/index.html)
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al.
Short antenna impedance and quality factor Coil + parallel capacitance for tuning antiresonance at operating frequency: V = 2π A·N·Eλ·cos(ϑ) × Q
Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
outdoor indoor ⇒ need to locate the antenna outdoor to get rid of lab-generated noise ⇒ need to introduce impedance converting circuit (antiresonance = maximize voltage with no current flow) + prevent Q degradation 9 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Lock-in + oscilloscope signal reception Experiment1: phase of the carrier and amplitude modulation detection
J.-M Friedt & al. Introductions VLF reception
Cs 10 MHz SMC100
77500
AM v.s PM Sound card SDR DVB-T: sampling resolution ?
computer
ethernet
lock in amplifier ref in phase mag CH1
CH2
digital oscilloscope
Conclusion References
Internal synthesizer quartz reference
• AM: 100 or 200 ms
long amplitude drop at the beginning of each second • ϕ: ∆ω · t + ϕ(t)
10 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Lock-in + oscilloscope signal reception Experiment1: phase of the carrier and amplitude modulation detection
J.-M Friedt & al. Introductions VLF reception
Cs 10 MHz SMC100
77500
AM v.s PM Sound card SDR DVB-T: sampling resolution ?
computer
ethernet
lock in amplifier ref in phase mag CH1
CH2
digital oscilloscope
Conclusion References
Synthesizer locked on Cs reference
• AM: 100 or 200 ms
long amplitude drop at the beginning of each second • ϕ: ∆ω · t + ϕ(t)
11 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Lock-in + oscilloscope signal reception Experiment1: phase of the carrier and amplitude modulation detection
J.-M Friedt & al. Introductions VLF reception
Cs 10 MHz SMC100
77500
AM v.s PM Sound card SDR DVB-T: sampling resolution ?
computer
ethernet
lock in amplifier ref in phase mag CH1
CH2
digital oscilloscope
Conclusion References
Amplitude+phase+raw data @ >200 kS/s
• AM: 100 or 200 ms
long amplitude drop at the beginning of each second • ϕ: ∆ω · t + ϕ(t)
12 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Phase-modulated spectrum spreading • Phase demodulation cross-correlation peak: 120 periods at
J.-M Friedt & al. Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ?
77.5 kHz=1.55 ms/bit • 700 Hz bandwidth needed for phase modulation processing • 511 bit long PRN 1 : x 9 + x 5 + 1
in lfsr.dat 0000010001100001001110010101011000011011110100110111001000101000010101101001111110110010010010110111111001001 1010100110011000000011000110010100011010010111111101000101100011101011001011001111000111110111010000011010110 1101110110000010110101111101010101000000101001010111100101110111000000111001110100100111101011101010001001000 0110011100001011110110110011010000111011110000111111111000001111011111000101110011001000001001010011101101000 1111001111100110110001010100100011100011011010101110001001100010001000000001
• interpolate the PRN sequence to match sampling rate, and cross-correlate
Conclusion 4e+06
+ parabolic fit of |xcorr ()| max
3e+06 xcorr (a.u.)
load l f s r . dat np =192000/59∗(120/77500) ; % f s ∗( Tprn /fDCF ) o l d P =0; f o r k =1: l e n g t h ( l f s r ) P=r o u n d ( k∗np ) ; i f ( l f s r ( k ) ==1) i l f s r ( o l d P +1:P)=o n e s (P−oldP , 1 ) ; e l s e i l f s r ( o l d P +1:P)=z e r o s (P−oldP , 1 ) ; endif o l d P=P ; end y c=x c o r r ( xp−mean ( xp ) , i l f s r −mean ( i l f s r ) ) ;
2e+06
1e+06
0 0
2
4 time (s)
6
8
4e+06
3e+06 xcorr (a.u.)
References
2e+06
1e+06
0 3.97
3.98
3.99 time (s)
4
1 https://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_
4/4.4_zeit_und_frequenz/pdf/5_1988_Hetzel_-_Proc_EFTF_88.pdf
13 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions
Resolution gain by using phase rather than amplitude Oscilloscope: sampling rate=5 kHz, duration=50 s (250 ksamples=1.8 MB/chan/min) record phase+amplitude ⇒ cross-correlate PRN and phase 50-s acquisition
Zoom
10000
10000
5000
5000
6000
VLF reception 0 -5000 -10000 30 40 time (s)
50
60
-8000 0
abs(xcorr(ph,prn))
abs(xcorr(ph,prn))
0
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2
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1.9
1.95 time (s)
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1.9
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2.05
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600 800 sample number (5 kS/s)
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10000 xcorr(phase,PRN)
References
20
1e+06
Conclusion
10
2000
-2000 -4000
-10000 0
DVB-T: sampling resolution ?
0 -5000
abs(xcorr(ph,prn))
Sound card SDR
amplitude
amplitude
amplitude
AM v.s PM
4000
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600000
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14 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception
Full SDR solution using gnuradio
2
• Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
AM v.s PM
f=192 kHz+df
Sound card SDR
sound card
DVB-T: sampling resolution ?
GPS 1 PPS
channel1 channel2
Conclusion
Cs 10 MHz SMC100
References
computer
77500
lock in amplifier ref in phase mag CH1
ethernet
CH2
digital oscilloscope
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when
adding second (GPS) path ? 2 dsPIC-based
based DCF receiver: http://www.marvellconsultants.com/DCF 15 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Full SDR solution using gnuradio • Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
Introductions VLF reception AM v.s PM
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
Sound card SDR
exp(−j*f*t)
exp(j*f*t)
Pexp(−j*f*t)
exp(j*f*t)
Baseband
Conclusion References
155−96=59 kHz
DVB-T: sampling resolution ?
77,5+77,5=155 kHz
J.-M Friedt & al.
−fe/2 +fe/2 −96 −77.5 77.5 96 155 f (kHz) real signal => even spectrum
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when
adding second (GPS) path ? 16 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception
Full SDR solution using gnuradio • Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when
adding second (GPS) path ? 17 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception
Full SDR solution using gnuradio • Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when
adding second (GPS) path ? 18 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception
Full SDR solution using gnuradio • Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when
adding second (GPS) path ? 19 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions VLF reception
Full SDR solution using gnuradio • Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when
adding second (GPS) path ? 20 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Full SDR solution using gnuradio • Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
J.-M Friedt & al. Introductions VLF reception AM v.s PM
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
Sound card SDR DVB-T: sampling resolution ? Conclusion References
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when adding second (GPS) path ? 21 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Full SDR solution using gnuradio • Frequency translation and low-pass filter (lockin): Xlating FIR Filter • Once baseband is reached, decimate (low pass filter to prevent
J.-M Friedt & al. Introductions VLF reception AM v.s PM
aliasing and 1 in N) – here N=59 • (192000/59)/(77500/120) ' 5.0388 : 5 samples/bit • Sound card sampling frequency fluctuation ⇒ record GPS 1 PPS
Sound card SDR DVB-T: sampling resolution ? Conclusion References
• Sound card offset to nominal frequency: 1.15 Hz @
77.5 kHz=15 ppm • Lack of continuity of the GNURadio oscilloscope output when adding second (GPS) path ? 22 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al.
Sound card SDR GNURadio is a python script generator, no need for a graphical interface 1 run periodically acquisition script 2 process resulting dataset using GNU Octave
Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
Implementation using Octave of FIR+xcorr: xcorr (a, b) 6= xcorr (b, a) 0.001 0.0005 0 0
5
10
15
20
25
15
20
25
15
20
25
time (s)
phase (rad)
4 2
x=r e a d c o m p l e x b i n a r y ( f i l e n a m e ) ; d c f=r e a l ( x ) ; g p s=imag ( x ) ; f e =192 e3 ; t i m e = [ 0 : l e n g t h ( x ) −1] ’/ f e ; d c f=d c f .∗ e x p ( j ∗2∗ p i ∗(77500)∗t i m e ) ; l p f = f i r l s ( 2 5 0 , [ 0 720 790 f e /2]∗2/ f e , [ 1 1 0 0 ] ) ; d c f= f i l t e r ( l p f , 1 , d c f ) ; x=d c f ( 1 : 5 9 : end ) ; f e =192000/59;
0 -2 -4 0
5
10 time (s)
xcorr(phase,code)
amplitude (a.u.)
0.002 0.0015
400 300 200 100 0 0
5
10 time (s)
[ y f , x f ]=max ( a b s ( f f t ( x−mean ( x ) ) ) ) ; x f=x f−l e n g t h ( x ) −1; d f=−x f / l e n g t h ( x )∗ f e ; l o=e x p ( j ∗2∗ p i ∗d f∗t i m e ) ; x=x .∗ l o ; xp0=mean ( a n g l e ( x ( 1 : 3 0 0 0 ) ) ) ; x=x.∗(− j ∗xp0 ) ; xp=a n g l e ( x ) ; y c=x c o r r ( xp−mean ( xp ) , i l f s r −mean ( i l f s r ) ) ; y c=y c ( f l o o r ( l e n g t h ( y c ) / 2 ) : end ) ; g g p s=g p s ( 1 : 5 9 : end ) ; 23 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al.
Sound card SDR GNURadio is a python script generator, no need for a graphical interface 1 run periodically acquisition script 2 process resulting dataset using GNU Octave
Introductions VLF reception AM v.s PM Sound card SDR DVB-T: sampling resolution ? Conclusion References
1 minute acquisition (60 seconds), red=xcorr max. to 1 PPS interval, blue=parabolic fit max. to 1 PPS Getting rid of outliers: use median value + average of samples lying at median±5 a.u. 24 / 32
J.-M Friedt & al. Introductions VLF reception
Cs v.s sound card+GPS 3-day measurement xcorr-1PPS position
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
663 662.5 662 661.5 661
AM v.s PM
20
40
60 time (h)
80
100
20
40
60 time (h)
80
100
20
40
60 time (h)
80
100
Sound card SDR
Conclusion
30000 DVB-T: sampling resolution ?
20000 10000 0 -10000
References
-20000
30000 20000 10000 0 -10000 -20000
σxcorr −1PPS (200samples) = 0.03 sample periods around time 60 h 192 kHz/59=3254 Hz=1/307 µs ⇒ σxcorr −1PPS = 9.2 µs∼2.8 km
25 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
DVB-T v.s sound card • Sampling frequency > 150 kHz (we only need up to 200 kS/s) 2 : is 8 bit sufficient to detect air v.s ground wave ? SNR = 6.02 · B + 1.76 + 10 log10 (fs /(2 · fmax )) with B16→8 & fs × = 10
• Sampling resolution J.-M Friedt & al. Introductions VLF reception
P
AM v.s PM
antenna transfer function
Sound card SDR DVB-T: sampling resolution ? Conclusion References
f jammer
airgnd fs/2
Problems: • the zero-IF E4000 based DVB-T receivers are obsolete • the newer R820T(2) based receivers use non-zero (3.57 MHz) IF ⇒ bypass RF frontend (capacitive decoupling of I-/Q-) ⇒ make the RTL2832U believe it is operating at zero-IF 2 J.
3
Mitola, Software Defined Radio Architecture, John Wiley & Sons (2000), p.293
3 http://superkuh.com/rtlsdr.html 26 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
DVB-T 1 2
J.-M Friedt & al.
hardware modification: I+=DCF77, Q+=GPS 1 PPS software modification: librtlsdr4 : src/librtlsdr.c, l.1580 [...] found : f p r i n t f ( s t d e r r , " dev tuner ,% x - > % x \ n " , dev−>t u n e r t y p e , → ,→RTLSDR TUNER E4000 ) ; dev−>t u n e r t y p e=RTLSDR TUNER E4000 ;
Introductions VLF reception
/∗ u s e t h e r t l c l o c k v a l u e by d e f a u l t ∗/ dev−>t u n x t a l = dev−>r t l x t a l ;
AM v.s PM Sound card SDR DVB-T: sampling resolution ?
3
Conclusion
replace gr-osmosdr source (complex=8 bytes/sample) with rtl sdr 1.92 MS/s during 1 minute=230 MB as char but 920 MB as float #! / b i n / s h w h i l e t r u e ; do r t l s d r −s 1920000 −n 115200000 /tmp/ d v b t . b i n nom=‘ d a t e +%s ‘ o c t a v e go .m > $nom . d a t mv 1 . e p s ${nom} 1 . e p s ; mv 2 . e p s ${nom} 2 . e p s ; mv 3 . e p s ${nom} 3 . e p s s l e e p 10 done
References
4
low-pass & decimate to reach 192 kHz, mix and low-pass+decimate: f s =1.92 e6 ; b= f i r l s ( 1 2 8 , [ 0 2 e5 2 . 5 e5 f s /2]∗2/ f s , [ 1 1 0 0 ] ) ; % 1 . 9 2 MHz/128=15 kHz r e s . d d c f= f i l t e r ( b , 1 , d d c f ) ; d d c f=d d c f ( 1 : 1 0 : end ) ; f s=f s / 1 0 ; % LPF/ dec i m =192 kHz t i m e = [ 0 : l e n g t h ( d d c f ) −1] ’/ f s ; d d c f=d d c f .∗ e x p ( i ∗t i m e∗2∗ p i ∗77493) ; % frequency transposition b= f i r l s ( 1 2 8 , [ 0 750 800 f s /2]∗2/ f s , [ 1 1 0 0 ] ) ; % LPF/ d eci m d d c f= f i l t e r ( b , 1 , d d c f ) ; d d c f=d d c f ( 1 : 5 9 : end ) ; f s=f s / 5 9 ;% LPF/ d eci m =3.254 kHz t i m e = [ 0 : l e n g t h ( d d c f ) −1] ’/ f s ;
4 https://github.com/steve-m/librtlsdr 27 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions
DVB-T Again, magnitude (AM) and phase (PM) demodulation functional, but now 1 PPS GPS signal identified with 520 ns resolution (10-fold improvement) 4 20 Hz LPF
Conclusion References
10
20
30 time (s)
40
50
60
2 1 0 -1 -2 -3
0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
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0
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time (s)
500 0
amplitude (a.u.)
DVB-T: sampling resolution ?
amplitude (a.u.)
0
3 phase (rad)
Sound card SDR
0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
10
20
30 time (s)
40
50
60
20 GPS 1 PPS
10 0 -10
xcorr(phase,code)
AM v.s PM
amplitude (a.u.)
blue=phase, red=linear fit, green=phase-lin. fit
VLF reception
400 300 200 100
-20 -30
0 0
10
20
30 time (s)
40
50
AM (20 Hz LPF), AM (50 LPF), GPS
60
0
10
20
30
40
50
60
70
time (s)
unwrapped phase, xcorr
Lower SNR ⇒ poorer cross-correlation peak location in time 28 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals J.-M Friedt & al. Introductions
DVB-T Again, magnitude (AM) and phase (PM) demodulation functional, but now 1 PPS GPS signal identified with 520 ns resolution (10-fold improvement)
Sound card SDR
0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
0.8 20 Hz LPF 0.6 0.4 0.2
Conclusion References
10
20
30 time (s)
40
50
60 0
0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
-0.2
50 Hz LPF
0
10
20
30
40
50
60
0
10
20
30 time (s)
40
50
60
-0.2 0
amplitude (a.u.)
DVB-T: sampling resolution ?
amplitude (a.u.)
0
10
20
30 time (s)
40
50
60
20 GPS 1 PPS
10
-0.4 tDCF-tGPS (s)
AM v.s PM
amplitude (a.u.)
0
VLF reception
0 -10
-0.6 -0.8 -1 -1.2
-20 -30
-1.4 0
10
20
30 time (s)
40
50
AM (20 Hz LPF), AM (50 LPF), GPS
60
GPS to DCF77 phase
Lower SNR ⇒ poorer cross-correlation peak location in time 29 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Conclusion and perspectives • Ability to receive DCF-77 using active antenna • Ability to decode DCF-77 using a lock-in amplifier and decode
phase modulation
J.-M Friedt & al. Introductions VLF reception AM v.s PM
• Ability to decode DCF-77 using SDR with signal acquired from c !) sound card & DVB-T receiver (how come that ∆z 2·B • Consistent results between Cs+lockin or sound card+GPS 10-6
Sound card SDR
400 delay (us)
DCF77 v.s GPS
DVB-T: sampling resolution ?
200
10-7 0 -200
Conclusion
avar (s)
-400 16-Dec 09h
References
date (day month hour)
X-ray flux (GOES)
5e-07
10-8 tuning fork
10-9
4e-07 3e-07
10-10
2e-07 1e-07 0 06-Nov 00h
26-Nov 00h
16-Dec 00h
05-Jan 00h
10-11 0 10
101
102
103 104 time (s)
105
106
107
• Question: if ground wave is strongest, why does its phase vary with
day/night ? (waveguide model) • Question: separate ground and air wave (improve xcorr resolution) ? • Microcontroller based sampling for high resolution 1 PPS timing 30 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
Conclusion and perspectives • Ability to receive DCF-77 using active antenna • Ability to decode DCF-77 using a lock-in amplifier and decode
phase modulation
J.-M Friedt & al. Introductions VLF reception AM v.s PM
• Ability to decode DCF-77 using SDR with signal acquired from c !) sound card & DVB-T receiver (how come that ∆z 2·B • Consistent results between Cs+lockin or sound card+GPS
Sound card SDR
CA code double CA CA code+1 CA code+2 CA code+3 CA code+4 CA code+5
400 delay (us)
DVB-T: sampling resolution ?
200
1.2
0
1 cross-correlation (a.u)
-200
Conclusion
-400 16-Dec 09h
References
date (day month hour)
X-ray flux (GOES)
5e-07 4e-07
0.8 0.6 0.4
3e-07
0.2
2e-07 1e-07
0 0 06-Nov 00h
26-Nov 00h
16-Dec 00h
05-Jan 00h
-30
-20
-10 0 10 time offset (sample number)
20
30
• Question: if ground wave is strongest, why does its phase vary with
day/night ? (waveguide model) • Question: separate ground and air wave (improve xcorr resolution) ? • Microcontroller based sampling for high resolution 1 PPS timing 31 / 32
Monitoring the ionosphere altitude variation with a sound card: software defined radio processing of DCF-77 signals
1 P.-H. Kamp, A Cheap SDR Loran-C frequency receiver at
phk.freebsd.dk/AducLoran/AducLoran-0.3.pdf 2 ARRL Antenna Handbook, Chapter5 (Small Loop Antennas), 18th Ed. (1997) 3 S.M.F. Raupach & G. Grosche, Chirped Frequency Transfer: A Tool for
J.-M Friedt & al.
4 Introductions
5
VLF reception AM v.s PM
6
Sound card SDR DVB-T: sampling resolution ?
7
Conclusion References
8 9 10 11
12
Synchronization and Time Transfer, IEEE Trans. Ultrasonics, Ferroelectrics, and Freq. Control 61 (6), June 2014 chirped freq time transfer.pdf K. Davies, Ionospheric Radio, IET (1990) P. Dolea & al., In-situ Measurements Regarding LF Radio Wave Propagation using DCF77 Time Signal Transmitter, TELSIKS 2013 P. Hetzel, Time dissemination via the LF transmitter DCF77 using a pseudo-random phase-shift keying of the carrier, 2nd EFTF (1988) A.D. Watt & al., Worldwide VLF Standard Frequency and Time Signal Broadcasting, J. of Research of the National Bureau of Standards 65D (6), 1961 W.T. Blackband, Propagation of Radio Waves at Frequencies below 300 kc/s (1964) A. Bauch & al., Time and Frequency Dissemination with DCF77: From 1959 to 2009 and beyond, PTB Mitteilungen 119 (3), 2009 J.R. Johler, Propagation of the Low-Frequency Radio Signal, Proc. IRE (1961) D. Engeler, Performance analysis and receiver architectures of DCF77 radio-controlled clocks, IEEE Trans. on Ultrasonics, Ferroelectrics, and Freq. Control 59 (5), 2012 D. Piester, A. Bauch & al., Time and Frequency Broadcast With DCF77, Proc. 43rd PTTI Systems and Appliocations Meeting (2012)
All references available on the Library Genesis, gen.lib.rus.ec 32 / 32
