Serial minimum shift keyed modulator including notch and bandpass filters

Claim 2

A serial minimum-shift keyed modulator comprising: (a) biphase modulator means having a first input for receiving a serial bit stream of data, a second input for receiving a relatively high frequency carrier, and an output for supplying the carrier biphase modulated by the serial bit stream; (b) a conversion filter coupled to said biphase modulator means and providing a minimum-shift keyed signal, said conversion filter including (1) a notch filter having a notch adjacent to the carrier frequency and in the frequency spectrum of the biphase modulator, and (2) a bandpass filter having a bandpass positioned to extend above and below the carrier frequency for the biphase modulated carrier, said notch and bandpass filters being coupled together to form the conversion filter.

Claim 3

A serial minimum-shift keyed modulator comprising: (a) biphase modulator means having a first input for receiving a serial bit stream of data, a second input for receiving a relatively high frequency carrier, and an output having thereon the carrier biphase modulated by the serial bit stream; and (b) a conversion filter connected to said biphase modulator means and providing a minimum-shift keyed signal, said conversion filter including (1) a notch filter having a notch at approximately f o -3/4T, and (2) a bandpass filter having a bandpass positioned to attenuate sidelobes on either side of a mainlobe, where f o is the carrier frequency for the biphase modulated carrier and T is the bit period of the bit stream, said notch and bandpass filters being coupled together to form the conversion filter.

Claim 4

A serial minimum-shift keyed modulator comprising: (a) biphase modulator means having a first input for receiving a serial bit stream of data, a second input for receiving a relatively high frequency carrier, and an output having thereon the carrier biphase modulated by the serial bit stream; and (b) a conversion filter connected to said biphase modulator means and providing a minimum-shift keyed signal, said conversion filter including (1) a notch filter having a notch at approximately f o -3/4T, and (2) a bandpass filter having a bandpass positioned to attenuate sidelobes on either side of a mainlobe, where f o is the carrier frequency for the biphase modulated carrier and T is the bit period of the bit stream, said notch and bandpass filters being coupled together to form the conversion filter.

Claim 5

A serial minimum-shift keyed modulator as claimed in claim 2 wherein the biphase modulator means includes a multiplier.

Claim 6

A serial minimum-shift keyed modulator as claimed in claim 2 wherein the notch filter includes a double-stub tuner.

Claim 7

A serial minimum-shift keyed modulator as claimed in claim 4 wherein the double-stub tuner has a second notch at approximately f o +5/4T.

Claim 8

A serial minimum-shift keyed modulator as claimed in claim 5 wherein the bandpass filter is a fourth-order Butterworth filter constructed so that the bandpass is centered at approximately f o +1/4T.

Claim 9

A serial minimum-shift keyed modulator as claimed in claim 2 wherein the bandpass filter is a second-order Butterworth filter having a bandpass centered at approximately f o .

Claim 10

A serial minimum-shift keyed modulator as claimed in claim 2 wherein the bandpass filter includes a Butterworth filter.

Claim 11

In a serial minimum-shift keyed modulator of the type including a biphase modulator for biphase modulating a carrier with a serial bit stream and a conversion filter for converting the biphase modulated signal to a minimum-shift keyed signal, a method of synthesizing the conversion filter comprising the steps of: (a) providing a notch filter with a notch frequency in the frequency spectrum of the biphase modulated signal; (b) providing a bandpass filter, the bandpass of which extends on either side of the frequency of the carrier; (c) connecting the notch filter and the bandpass filter to provide an input and an output of said conversion filter; and (d) selecting the number and frequency position of notches of the notch filter and selecting the type, center frequency, and bandwidth of the bandpass filter to optimize the envelope amplitude variations and the bit error rate.

Claim 12

In a serial minimum-shift keyed modulator of the type including a biphase modulator for biphase modulating a carrier with a serial bit stream and a conversion filter for converting the biphase modulated signal to a minimum-shift keyed signal, a method of synthesizing the conversion filter comprising the steps of: (a) providing a notch filter with a notch frequency in the frequency spectrum of the biphase modulated signal; (b) providing a bandpass filter, the bandpass of which extends on either side of the frequency of the carrier; (c) connecting the notch filter and the bandpass filter to provide an input and an output of said conversion filter; and (d) selecting the number and frequency position of notches of the notch filter and selecting the type, center frequency, and bandwidth of the bandpass filter to optimize the envelope amplitude variations and the bit error rate.

Claim 13

In a serial minimum-shift keyed modulator of the type including a biphase modulator for biphase modulating a carrier with a serial bit stream and a conversion filter for converting the biphase modulated signal to a minimum-shift keyed signal, a method of synthesizing the conversion filter comprising the steps of: (a) providing a notch filter with a notch frequency in the frequency spectrum of the biphase modulated signal; (b) providing a bandpass filter, the bandpass of which extends on either side of the frequency of the carrier; (c) connecting the notch filter and the bandpass filter to provide an input and an output of said conversion filter; and (d) selecting the number and frequency position of notches of the notch filter and selecting the type, center frequency, and bandwidth of the bandpass filter to provide a minimum-shift keyed signal having a frequency spectrum and a center lobe approximately equal in magnitude and width to the center lobe of a conversion filter having an impulse response ##EQU18##

Claim 14

In a serial minimum-shift keyed modulator of the type including a biphase modulator for biphase modulating a carrier with a serial bit stream and a conversion filter for converting the biphase modulated signal to a minimum-shift keyed signal, a method of synthesizing the conversion filter comprising the steps of: (a) providing a notch filter with a notch frequency in the frequency spectrum of the biphase modulated signal; (b) providing a bandpass filter, the bandpass of which extends on either side of the frequency of the carrier; (c) connecting the notch filter and the bandpass filter to provide an input and an output of said conversion filter; and (d) selecting the number and frequency position of notches of the notch filter and selecting the type, center frequency, and bandwidth of the bandpass filter to provide a minimum-shift keyed signal having a frequency spectrum and a center lobe approximately equal in magnitude and width to the center lobe of a conversion filter having an impulse response ##EQU18##