A new broadband frequency discriminator is introduced for demodulating the frequency modulated signals in the microwave frequency range. Direct demodulation with no need for tuning the center frequency of the resonance circuits is the most important advantage of the proposed technique. This technique uses the in-phase/quadrature demodulation, in some manner, without using any additional local oscillator for down conversion. Simulation of the proposed demodulator has been done with Advanced Design System software to evaluate and predict the system behavior. A setup based on the proposed method was designed and implemented in order to verify the accuracy of the theory. We tested the proposed frequency discriminator for FM signals at different microwave frequencies with various waveforms of the modulating signal. We also measured the bit error rate of the demodulator when the modulating signal is pseudorandom binary sequences for some data rates. To the best of our knowledge, this structure demonstrates the widest bandwidth direct demodulator without any tuning circuits among published FM demodulators to date.

An Ultra-Broadband Direct Demodulator for Microwave FM Receivers

Recently, continuous-valued optimization problems have received a great amount of focus, resulting in optimization algorithms which are very efficient within the continuousvalued space. Many optimization problems are, however, defined within the binaryvalued problem space. These continuous-valued optimization algorithms can not operate directly on a binary-valued problem representation, without algorithm adaptations because the mathematics used within these algorithms generally fails within a binary problem space. Unfortunately, such adaptations may alter the behavior of the algorithm, potentially degrading the performance of the original continuous-valued optimization algorithm. Additionally, binary representations present complications with respect to increasing problem dimensionality, interdependencies between dimensions, and a loss of precision. This research investigates the possiblity of applying continuous-valued optimization algorithms to solve binary-valued problems, without requiring algorithm adaptation. This is achieved through the application of a mapping technique, known as angle modulation. Angle modulation effectively addresses most of the problems associated with the use of a binary representation by abstracting a binary problem into a four-dimensional continuous-valued space, from which a binary solution is then obtained. The abstraction is obtained as a bit-generating function produced by a continuous-vaued algorithm. A binary solution is then obtained by sampling the bit-generating function. This thesis proposes a number of population-based angle-modulated continuousvalued algorithms to solve binary-valued problems. These algorithms are then compared to binary algorithm counterparts, using a suite of benchmark functions. Empirical analysis will show that the angle-modulated continuous-valued algorithms are viable alternatives to binary optimization algorithms.

Angle modulated population based algorithms to solve binary problems

The gyrator as a monolithic circuit in electronic systems

Practical methods of generating and receiving phase modulation are described which open up the possibility of using phase modulation as a communication system. A new receiver is described which uses an off-neutralized crystal filter and provides a simple practical receiver which has not been heretofore available for phase modulation. Other methods of reception are described and discussed. Propagation tests which were conducted between California and New York indicate that the propagation characteristics of phase modulation are substantially the same as those of amplitude modulation. The noise characteristics of phase modulation are considered and it is shown that the signal-noise ratio at the output of the phase-modulation receiver is equal to the product of the phase deviation in radians and the carrier-noise ratio. The chief advantage of phase modulation is realized at the transmitter where a power gain of about four-to-one is obtained and modulating equipment is reduced by the ability to modulate at a low level without the requirement of linearity in the stages following the modulator. The chief difficulty occurs at the receiver where the susceptibility to microphonics is increased and the circuits are slightly more complicated.

Communication by Phase Modulation

A Monolithic Limiter and Balanced Discriminator for FM and TV Receivers

The principles underlying automatic frequency control of the oscillator in superheterodyne receivers have been outlined in previous papers given before the Institute of Radio Engineers. This paper deals with simplification and improvements in operation of frequency control circuits and their application to automatic (electronic) tuning control. A new type of "discriminator" which differentiates between mis-tuned signals on the high-frequency side of resonance and those on the low-frequency side is described and its operation demonstrated by means of a visual frequency indicator. The operation of the discriminator is such that it may be used to supply audio-frequency components corresponding to the amplitude modulations of the received carrier wave and automatic volume control potentials as well as the control voltage for the frequency control circuits. This multifunction is described and illustrated. Alternative circuit connections to improve the compromise between discriminator sensitivity, audio fidelity, and selectivity are explained and illustrated. The use of vacuum tubes in such manner that they act as reactive components and the manner in which their apparent reactive impedance may be controlled by varying the tube parameters is demonstrated. The action of a complete receiver embodying automatic (electronic) tuning control in overcoming mis-tuning and oscillator frequency drift will be demonstrated.

S.W. Seeley

Papers

Automatic Tuning, Simplified Circuits, and Design Practice