Abstract: A frequency synthesizer apparatus is disclosed which combines a digital multiplier in the count down and phase comparison section with an oscillator entirely contained on an integrated circuit. Inclusion of the digital multiplier allows simultaneous realization of high loop bandwidth and fast tuning speed. The large loop bandwidth facilitates use of a totally integrated oscillator, which was heretofore not useable because of inferior phase noise characteristics. An integrated filter further enhances loop bandwidth while maintaining stability. Synchronizing the modulus switching of a multi-modulus prescaler with the multiplier coefficient minimizes spurious responses in the synthesized output.

Abstract: A digital filter is designed by characterizing a desired filter passband in the frequency domain, transforming this representation into the time domain, selecting weighting coefficients at periodically spaced intervals from this transformed function, and weighting the coefficients with a Gaussian windowing function. This function may take the form:.sub.e -.vertline.( 2 n-N)/A.vertline..sup.Pwhere:A=N(-ln.epsilon.).sup.-1/P; .epsilon.<1.epsilon.=Window value desired at n= 0 and n=N (reduction ratio);N=(number of F.I.R. taps)- 1; andP=an arbitrary power.

Abstract: In a ratio paging system of the type having digital data modulated onto radio signals transmitted from a radio station to receiving units at remote sites, a test system. The test system includes a transmitter test module coupled to a radio transmitter at the station and a test bed module located at the remote site. The transmitter test module includes a microprocessor for generating digital test data, and a modulator coupled to the microprocessor for modulating the test data onto a radio signal and for injecting the radio signal into the station transmitter. The test bed includes a receiver for receiving the modulated radio signal, a demodulator for demodulating the received radio signal to recover the digital test data, and a computer for processing the recovered digital test data to generate paging test information. The mobile test bed also includes means for determining the latitude and longitude of a site to generate digital location data which is used to generate test information.

Abstract: A direct conversion FM receiver that includes AC coupling and automatic gain control employs an offset frequency at the first local oscillator. The offset frequency prevents the frequency spectrum occupied by the signal modulation from being affected by AC coupling. The offset frequency is chosen so that it translates the frequency spectrum of the received signal outside the DC notch created in the spectrum by the AC coupling. To conserve battery supplied power, an error amplifier coupled between the output of the receiver and the first local oscillator maintains the offset frequency after it has been established by a frequency synthesizer, which is then turned off.

Abstract: A digital receiver samples data from an amplitude modulated subcarrier at a rate less than twice the subcarrier's maximum frequency by sampling at known phase points. Sampling at known phase points is achieved by generating a sampling clock from a signal phase locked to and transmitted with the modulated data subcarrier.