The document discusses software defined radio (SDR) technology, including how it works and a demonstration. It covers modulation techniques like amplitude modulation and frequency modulation. It describes the components of simple and modern radio receivers. It explains how SDR samples and processes radio signals using in-phase and quadrature sampling. It provides details about a low-cost SDR dongle called the FCD and software like GNU Radio that can be used for SDR. It concludes with an offer to provide a live demonstration of SDR capabilities.
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Drahtlose Kommunikation und SDR
1. Introduction modulation Receivers, how do they work? SDR Demo
SDR a short introduction
Oliver Wisler
March 27, 2014
Oliver Wisler
SDR a short introduction
2. Introduction modulation Receivers, how do they work? SDR Demo
1 Introduction
2 modulation
amplitude modulation
frequency modulation
phase shift keying
other modulations
3 Receivers, how do they work?
simple receiver
modern receivers
4 SDR
How does it work?
legal Boundaries
5 Demo
Oliver Wisler
SDR a short introduction
3. Introduction modulation Receivers, how do they work? SDR Demo
technical terms
RX receiver
TX transmitter
HF high frequency, general term for radio frequencies
LF low frequency, everything audible
SNR signal to noise ratio, quantifies the quality of reception
Oliver Wisler
SDR a short introduction
4. Introduction modulation Receivers, how do they work? SDR Demo
frequency ranges
<3 MHz VLF submarines
3-30 MHz HF ham radio, worldwide communication
30-300 MHz VHF broadcasting, handheld radio
300-3 GHz UHF WLAN, microwave, GPS
>3 GHz SHF radar, astronomy, satellites
Oliver Wisler
SDR a short introduction
5. Introduction modulation Receivers, how do they work? SDR Demo
modulation, what’s that?
Definition
a process of mixing different signals to obtain a new one
usually one of these signal is sinusoid
tech term for converting LF to HF
Oliver Wisler
SDR a short introduction
6. Introduction modulation Receivers, how do they work? SDR Demo
amplitude modulation
amplitude modulation
invented around 1900
one of the first methods to transmit voice
easy and cheap to receive (”Volksempf¨anger” in WW2)
prone to interference
wastes a lot of energy transmitting the carrier
has a small bandwidth (even less with SSB)
still used for HF (< 30Mhz) broadcasts
Oliver Wisler
SDR a short introduction
7. Introduction modulation Receivers, how do they work? SDR Demo
amplitude modulation
AM problem
time
amplitude
carrier
signal
Oliver Wisler
SDR a short introduction
8. Introduction modulation Receivers, how do they work? SDR Demo
amplitude modulation
amplitude modulation
time
amplitude
carrier
signal
AM
Oliver Wisler
SDR a short introduction
9. Introduction modulation Receivers, how do they work? SDR Demo
amplitude modulation
amplitude modulation minimal schema
Oliver Wisler
SDR a short introduction
10. Introduction modulation Receivers, how do they work? SDR Demo
amplitude modulation
amplitude modulation detail
time
amplitude
carrier
signal
Oliver Wisler
SDR a short introduction
11. Introduction modulation Receivers, how do they work? SDR Demo
amplitude modulation
amplitude modulation spectrum
frequency
power
LSB USB
signal
carrier
Oliver Wisler
SDR a short introduction
12. Introduction modulation Receivers, how do they work? SDR Demo
frequency modulation
frequency modulation
patented 1933
better SNR than AM when good reception
needs more bandwidth than AM
widely used for frequencies above 30Mhz
Oliver Wisler
SDR a short introduction
13. Introduction modulation Receivers, how do they work? SDR Demo
frequency modulation
FM problem
time
amplitude
carrier
signal
Oliver Wisler
SDR a short introduction
14. Introduction modulation Receivers, how do they work? SDR Demo
frequency modulation
frequency modulation
time
amplitude
signal
FM
Oliver Wisler
SDR a short introduction
15. Introduction modulation Receivers, how do they work? SDR Demo
frequency modulation
frequency modulation spectrum
frequency
power
Oliver Wisler
SDR a short introduction
16. Introduction modulation Receivers, how do they work? SDR Demo
phase shift keying
PSK problem
time
amplitude
signal
0 1 1 0
Oliver Wisler
SDR a short introduction
17. Introduction modulation Receivers, how do they work? SDR Demo
other modulations
other types of modulations
QPSK PSK with φ = π
2 , each shift encodes 2 bits
FSK encode bits with 2 frequencies
QAM combination of AM and PSK, up to 12 bits per symbol
Oliver Wisler
SDR a short introduction
18. Introduction modulation Receivers, how do they work? SDR Demo
simple receiver
simple AM receiver schema
antenna
filter amplifier demodulator amplifier
speaker
receiver
Oliver Wisler
SDR a short introduction
19. Introduction modulation Receivers, how do they work? SDR Demo
simple receiver
filter
frequency
power
interference
Oliver Wisler
SDR a short introduction
20. Introduction modulation Receivers, how do they work? SDR Demo
simple receiver
amplifier
amplifies the signal for demodulation
needs to be linear (at least for AM)
Oliver Wisler
SDR a short introduction
21. Introduction modulation Receivers, how do they work? SDR Demo
simple receiver
demodulator
a simple diode and two capacitors
Oliver Wisler
SDR a short introduction
22. Introduction modulation Receivers, how do they work? SDR Demo
modern receivers
Improving our receiver
how/where can we improve our simple receiver?
Oliver Wisler
SDR a short introduction
23. Introduction modulation Receivers, how do they work? SDR Demo
modern receivers
better filters
using 2 bandwidth filters
steeper flanks
special filters (eg notch)
if we could fix the frequency, we could design better filters
frequency
power
interference
Oliver Wisler
SDR a short introduction
24. Introduction modulation Receivers, how do they work? SDR Demo
modern receivers
better receiver
antenna
preamplifier mixer filter amplifier demodulator amplifier
oscillator speaker
mixing down fixed frequency
Oliver Wisler
SDR a short introduction
25. Introduction modulation Receivers, how do they work? SDR Demo
modern receivers
better antenna
most important part
many different designs available
Oliver Wisler
SDR a short introduction
26. Introduction modulation Receivers, how do they work? SDR Demo
modern receivers
receivers today
2nd mixer&filter stage
adjustable oscillators (VCO)
better demodulator
superheterodyne receiver
Oliver Wisler
SDR a short introduction
28. Introduction modulation Receivers, how do they work? SDR Demo
How does it work?
IQ
we could just sample a signal at its Nyquist frequency
difficult to process
idea two samples short after each other
Oliver Wisler
SDR a short introduction
29. Introduction modulation Receivers, how do they work? SDR Demo
How does it work?
allows extraction of phase information
removes ambiguity of frequency mixing
Q
I
Oliver Wisler
SDR a short introduction
30. Introduction modulation Receivers, how do they work? SDR Demo
How does it work?
FCD
Project by HamSat
small, relatively cheap SDR
Range: 0.150MHz - 206MHz, 403MHz-2GHz (all Ham-radio
bands)
Resolution: 16Bit / 192kHz
Oliver Wisler
SDR a short introduction
31. Introduction modulation Receivers, how do they work? SDR Demo
How does it work?
FCD schema
i2s sound serial bus
i2c serial bus
Oliver Wisler
SDR a short introduction
32. Introduction modulation Receivers, how do they work? SDR Demo
How does it work?
FCD filter
LNA low noise amplifier
Oliver Wisler
SDR a short introduction
33. Introduction modulation Receivers, how do they work? SDR Demo
How does it work?
Software
gnuradio
gqrx
quisk
Oliver Wisler
SDR a short introduction
35. Introduction modulation Receivers, how do they work? SDR Demo
sources
DJ4UF Amateurfunklehrgang
http://whiteboard.ping.se/SDR/IQ
Datasheet of the FCD
Pictures Wikipedia
Oliver Wisler
SDR a short introduction