A New Principle for Measuring Electrical Length and Deviation from Linear Phase
This paper presents a unique way to measure the equivalent electrical length of a network as well as its deviation from linear phase. The measurement technique used is based upon a variable length transmission line simulator, built into the IF-structure of a 1.3 GHz Network Analyzer, but can be applied to higher frequencies. The new method allows to insert much more electrical length than the mechanical line stretchers do, without disturbing the measurement with additional mismatch errors. In addition to a calibrated readout of the equivalent electrical length in meters, the deviations from linear phase of a network can be presented very accurately in a real time swept display.
The Interpretation of Amplitude and Phase Distortion in Terms of Paired Echoes
In picture-transmission systems, such as television and facsimile, the signal transients are noticeably distorted by small amounts of amplitude and phase distortion. There has been developed a simple method of estimating the effects of such distortion from inspection of the amplitude and phase curves. The distortion is regarded as made up of a pattern of echoes, each echo corresponding to a small amount of distortion of both kinds. The separate interpretation of amplitude and phase distortion requires pairs of echoes, those of each pair being equally displaced in time before and after the signal output. This is called the "method of paired echoes." Amplitude distortion corresponds to symmetrical "positive" pairs whereas phase distortion corresponds to skew-symmetrical "negative" pairs. A complete and exact theory is presented on the basis of a small amount of distortion. The method of paired echoes is most useful in the interpretation of phase curves and the determination of the tolerance of phase distortion.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.