Estimates Of distributions of ranfor high-speed digital computers. F~~~ 1964 to 1966 he was Phoenix, Ariz., where he was engaged in the development of switching dom variables for certain computer communications traffic n,," l o 7 n where he worked in the area of information processing in random model,!! Commun. Ass. Comput. Mach,, ~0 1 . 13, pp, 752-757, Absfracf-Minimum (frequency) shift keying (MSK) is a digital modulation technique which can be viewed either as frequency-shift keying (FSK) with peak frequency deviation precisely equal to f (1/4)RL where RL isthe link bit rate or as an offset-keyed quaternaryphase-shift-keyed modulation. In the absence of bandwidth or amplitude limiting between the modulator and the demodulator, the Eb/Niperformance of MSK is identical to that of coherently detected binary phase-shift keying (PSK). This paper briefly reviews and defines MSK. It then presents a system model in which a tandem assembly of a transmit band-limiting filter, a hard limiter, and a receive band-limiting filter are interposed between an ideal modulator and demodulator. This model is aimed at simulating actual links (such as spacecraft-to-ground links) i i~ which channel bandwidth (Bc) constraints are important, postmodu!ation filtering at RF is objectionable, and transmission through efficient transmitters which operate as amplitude limiters is a requirement.An analysis then derives the Eb/No degradation due to both bandwidth and amplitude limiting. Band limiting alone causes intersymbol interference on the data carried by each of the quadrature phasors but no interphasor crosstalk under the set of assumptions used. With amplitude limiting also present, an interphasor crosstalk mechanism exists. The average symbol distortion, symbol energy reduction, and noise reduction are derived for several periodic waveforms. For composite systems with 3-dB bandwidth (BL)-to-RL Electronics of the IEEE Communications Society for publication Paper approved by the Associate Editor for Communication without oral presentation. Manuscript Corporation, Princeton, N. J. 08540. The authors are with the Astro Electronics Division, RCA ratios of at least 0.6, the theoretical ,%/No degradation is less than 1 dB.Parametric experimental data are then reported on the ,postmodulation spectrum of a transmitter with band limiting plus subs& quent hard amplitude limiting. Data are also presented ,on the &/No degradation measured using tandem assemblies of a bandlimiting filter, an amplitude limiter, and a second band-limiting filter.The amplitude limiter substantially increa$es the level of the spectral side lobes beyond the main lobe. It was found that for all significant values of transmit bandpass filtering plus subsequent amplitude limiting, 99 percent of the transmitted energy is containedFurther, little Eb/No degradation (tenths of a decibel) was measured if BL was greater than 0.65 RL. A rapid degradation of &,/No occurred when BL = 0.55 RL. These data apply for the band-amplitude-band limited system model.The amplitude limiter...

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order to obtain stable closed-loop operation. With feedback the amplifier is driven over the linear region with a 60cps signal of less than 1.0 mv (millivolts). The voltage gain is about 15,000 and the power gain is 4XI0 8 • Considering the increased input impedance, the amplifier is driven over the linear range with 10-9 watts to produce full output. The use of high-supply frequency and capacitive coupling extends a-c magnetic-amplifier sensitivity by several orders of magnitude. In addition, a capacitively coupled amplifier possesses high speed, phase sensitivity, excellent stability, and good linearity. Low-level d-e signals also can be amplified and these features retained if a powerfrequency chopper is used on the input of the amplifier.T H E INCREASE in demand for communication service throughout the world has exceeded the rate of growth in population and the tremendous expansion of industrial activities.' Both civilian and military requirements have grown beyond the expectations of those associated with the communication field. Along with this need for increased capacities in communication networks, the need has developed for more reliable, higher quality communication service. Military operations and the defense of a country are dependent on the ability to communicate rapidly and accurately. Likewise the operations of large industrial organizations are controlled by signals transmitted over long distances. With these factors in view the M M-600 radio relay system described in this paper was developed. It is intended for use in major communication networks to transmit large numbers of signals from one central location to another over distances up to 4,000 miles. It was designed for common-carrier-type applications where reliability, excellence of performance, and ease of maintenance are of paramount importance. New components such as Conclusions A high-performance a-c magnetic amplifier can be constructed by using a highcarrier frequency and capacitively coupling the signal-frequency power to the load. . This technique realizes the advantages of a true a-c amplifier which include freedom from the effects of d-e drift, consequent increased sensitivity, elimination of an input demodulator, inherent phase sensitivity, and accurate reproduction of the input waveform. A capacitively coupled magnetic amplifier possesses excellent stability, and when amplifying power-frequency signals, can achieve very high voltage and power gains. A 3-stage amplifier has been built which has an equivalent noise level of 5J.Lv, or