Amplitude Modulation Noise Research Articles

Transition noise model for longitudinal thin-film media

The integrated noise power in longitudinal thin-film media increases with transition density. This behavior has been attributed to transition noise predominating over the more conventional amplitude modulation noise. At low recording densities the total noise power increases linearly with the transition density. At higher recording densities the noise increases more rapidly. The departure from the linear noise power increase with transition density has been attributed to correlation between noise in adjacent transitions. A model is presented for the noise process in longitudinal thin-film media, assuming that each transition's position fluctuation is correlated to the previous transition's position fluctuation by the demagnetization field. The dominant effect of the demagnetization fields is to increase the inherent noise in each transition and broaden the transitions as the recording density increases. It is the inherent noise increase in each transition, rather than the contribution from the adjacent transition correlation noise power term, that explains the experimentally found nonlinear noise power increase at higher transition densities. The frequency dependence of the integrated noise power is shown to be a strong function of the transition shape.

Comparison of AM Noise from a Klystron and an IMPATT Oscillator at Around 90 GHz

This paper reports comparisons between the amplitude modulation noise performance of a Plessey IMPATT oscillator AT0273 and a Varian VRB-2113 klystron at millimeter wavelengths.

IMPATT Pump Sideband Noise and its Effect on Parametric Amplifier Noise Temperature

This paper describes an investigation of the amplitude modulation (AM) noise sidebands of silicon IMPATT microwave oscillators and the effect these noise sidebands have on the excess noise temperature of parametric amplifiers. It is shown that the noise temperature may be affected under both large- and small-signal conditions to an extent which depends on the level of pump sideband noise. Simple relationships between easily measurable amplifier properties and pump noise power are given which enable the performance of any combination of pump and amplifier under the two signal conditions to be predicted. A method which simultaneously eliminates the small-signal effect and reduces the large-signal effect to an acceptable level is proposed and demonstrated to be a practical solution.

Noise spectra of beam-type microwave oscillators

The paper describes measurements of amplitude modulation,frequency modulation and total noise spectra for several types of klystrons and backward-wave oscillators. Computations of the noise to be expected have also been carried out and the theoretical and experimental results are compared.

Frequency synchronization of an X-band reflex klystron

The paper gives results obtained in synchronizing an X-band reflex klystron oscillator to a source of power at a similar frequency. The power is fed through an isolator to the oscillator so that synchronization is attempted in one direction only. The results show the variation of control range and power output with various parameters of the system. A number of applications of the phenomenon are discussed.The valve used in the work was the K302 with an output of about 20 mW. An incident power of less than 1 μW is sufficient to lock this valve.In addition, the energy distribution of the noise in a small bandwidth in the range 3–80 kc/s from the carrier was investigated for both locked and unlocked oscillator. Brief mention is made of the method of measurement. Using a source of locking power with a narrow energy distribution the relationship between this energy distribution and that of the locked oscillator is discussed as a function of incident power. It is shown that the amplitude-modulation noise distribution of the locked oscillator becomes identical to that of the locking source independently of the locking power, always provided that it remains locked and that the frequency-modulation noise distribution is a function of the locking power, being identical to that of the source for large locking powers and degenerating as the locking power is reduced. This provides a means of improving the noise distribution of a noisy reflex oscillator.The f.m. noise spectrum is measured in terms of the r.m.s. deviation in a small bandwidth at some distance from the carrier. It is shown that for a small deviation ratio (δ) the power in the bandwidth of measurement is given by ½δ2, relative to the carrier power.The contribution of the local-oscillator noise spectrum to the noise spectrum of the i.f. output from a balanced mixer is investigated and is shown to be as important as that of the noise distribution in the signal.

Modulation noise in magnetic tape recordings

Modulation noise remains as a major limitation on the dynamic signal-to-noise ratio obtainable in a magnetic recording system. The sources of modulation noise in magnetic tape recordings have been investigated by reducing to the smallest possible value the inherent noise of the recording and playback equipment used in the tests. Possible causes of modulation noise are then independently introduced and their effects measured. The results of these measurements indicate that when recording and reproducing equipment is properly adjusted, the major source of modulation noise is spurious amplitude modulation of the recorded signal by variations in the physical and magnetic properties of the recording tape. The amount of this modulation noise is found to increase above the value obtained with a dc signal, in proportion to the recorded signal frequency. Recommendations are made for measurement of amplitude modulation noise as a check on tape quality and on those adjustments which affect amplitude modulation noise. This measurement is in addition to the measurement of frequency modulation noise commonly known as "flutter."

Klystron oscillator noise theory

Results are presented of calculations on the amplitude and frequency fluctuations generated in a floating-drift-tube klystron oscillator by thermal noise in the cavity and current and velocity noise on the electron beam. Current fluctuations at the oscillation and harmonic frequencies are found to be the main source of frequency and amplitude modulation noise. At the very lowest modulation frequencies flicker noise in the beam will take over as the source of a.m. noise. The predominant f.m. source in this region is uncertain. Methods of reducing the noise are pointed out.