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Detection of wide band FSK signals with a narrow band scanning receiver

IP.com Disclosure Number: IPCOM000115700D
Publication Date: 2005-Mar-30
Document File: 1 page(s) / 11K

Publishing Venue

The IP.com Prior Art Database

Abstract

A narrow band scanning receiver is known for detecting ASK-modulated signals. Such a narrow band receiver allows for poor tolerance transmissions by scanning across the band and finding the wanted signal. This gives the narrow band advantages of noise rejection and good sensitivity. To enhance the interference rejection, the wanted signal is transmitted on two frequencies in case one of the frequencies is exactly the same as an interferer.

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Detection of wide band FSK signals with a narrow band scanning receiver

A narrow band scanning receiver is known for detecting ASK-modulated signals.  Such a narrow band receiver allows for poor tolerance transmissions by scanning across the band and finding the wanted signal.  This gives the narrow band advantages of noise rejection and good sensitivity.  To enhance the interference rejection, the wanted signal is transmitted on two frequencies in case one of the frequencies is exactly the same as an interferer.

This works particularly well for vehicle security systems where the signals are typically ASK- modulated and occupy a narrow bandwidth. In contrast, many tyre pressure measurement transmitters use a wideband FSK transmission, ie. a signal which conveys data by alternating between two frequencies about 100kHz apart. This would normally require a receiver  bandwidth much greater than 100kHz with the disadvantage that an interferer anywhere within this larger window will cause loss of reception.

However, if the wide band FSK. signal is treated as two ASK. signals with a phase lag of 180°, as is commonly done in mathematical treatments of WFSK, the same narrow band ASK. receiver can be used for detection.

To receive the signal, scan across the band as before with an ASK demodulator and a narrow bandwidth, say 30kHz.. The receiver finds one of the WFSK frequencies and also finds the ASK data which is demodulated.  If it finds the second WFSK frequency, the data wil...