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Publikationer från KTH
Bachelor thesis . 2025
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Spectrum Sensor and In-band Interference Suppression : Suppressing Interference Before it Becomes a Problem

Authors: Lindohf, Harald;

Spectrum Sensor and In-band Interference Suppression : Suppressing Interference Before it Becomes a Problem

Abstract

All receivers, especially wide band ones, are sensitive to strong interfering signals. Due to non-linearities, strong interference can cause unwanted spurious signals to appear in the received band. These spurs can be mistaken for, or obscure signals of interest, giving false information about the received spectrum and the surrounding electromagnetic environment. Additionally, if the signal is strong enough, the receiver may even be damaged. This vulnerability is especially problematic in defence applications, where misleading information can lead to bad decision-making and reliability is highly important. In order to address this problem, an early prototype of a Spectrum sensor has been developed at SAAB (patent pending). This sensor generates DC voltages that are dependent on the power and frequency of an incoming signal. These signals can be used to control a fix filter bank in order to selectively filter out unwanted interference before it reaches the receiver front end. The project at hand is to implement this sensor in such a system. The sensor prototype was first adjusted and characterised such that the frequency of an incoming signal can be determined from the output voltage. A filter bank was designed and manufactured consisting of three different notch filters and a bypass path. Having defined the spectrum sensor output signals and the filter bank input signals, a control circuit was designed and constructed. The control circuit takes the DC voltages from the spectrum sensor and controls the filter bank such that the most appropriate filter is applied to the signal path. The final system was assembled and tested, and achieved robust interference suppression with a response time below 100 ns. While some simplifications were made to the final system, it was able to demonstrate the function of the spectrum sensor, while offering valuable insight into it’s implementation. Alla mottagare är känsliga för starka störsignaler. Störning kan på grund av icke-linearitet i mottagaren göra att falska signaler genereras och tas emot. Dessa falska signaler kan skymma eller misstolkas som nyttosignaler och därmed ge en falsk bild av det mottagna spektrumet och den elektromagnetiska miljön i området. Om signalen är stark nog så kan mottagaren dessutom skadas. Denna svaghet särskilt problematisk i försvarssammanhang, då falsk information kan leda till felaktiga beslut och det finns höga krav på driftsäkerhet. För att lösa detta problem så har en tidig prototyp av en spektrumsensor utvecklats hos SAAB (patentansökan inskickad). Sensorns utspänningar beror på den inkommande signalens frekvens och amplitud. En filterbank kan med denna information styras så att inkommande störsignaler filtreras ut innan de kan orsaka problem i mottagaren. Det aktuella projektet går ut på att implementera ett sådant system med sensorprototypen. Sensorn har karaktäriserats och justerats så att frekvensen kan bestämmas utifrån utspänningen. En filterbank utvecklades med tre bandstopfilter och en förbikoppling. Med spektrumsensorns utsignaler och filterbankens insignaler definierade utvecklades ett kontrollkort som används för att kontrollera filterbanken utifrån informationen från spektrumsensorn. Kontrolkortet ser till att den mest passande filterbanksvägen sätts in efter spektrumsensorn. Det färdiga systemet undertrycker med säkerhet inkommande störsignaler med en svarstid under 100 ns. Det färdiga systemet är på vissa sätt förenklat jämfört med en framtida produkt, men utgör ändå en effektiv demonstration av spektrumsensorns egenskaper och förmågor. Projektet gav värdeful insikt i hur spektrumsensorn kan användas och implementeras.

Related Organizations
Keywords

Interferensdämpning, Bredbandsmottagare, Spectrum sensor, wide band receiver, Interference suppression, Spektrumsensor, Electrical Engineering, Electronic Engineering, Information Engineering, Filterbank, Elektroteknik och elektronik, Spurious signal suppression, Filter bank

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
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