Varactor Tuners Eliminated an RF Amplifier
There is an urgent demand for low noise varactor tuners for use in TV receivers to meet the requirements of FCC rules. The RF amplifier has been frequently eliminated in mechanical tuners now in use, resulting in good cross-modulation characteristics and low cost. However, the elimination of the RF amplifier has not been attained in varactor tuners, because of high series resistance of varactor diodes. The series resistance of Si diodes at 470 MHz is around 0.7Ω, and is much higher than that of mechanical capacitor, 0.15Ω. To reduce the noise figure of varactor tuners, tuning diodes with low resistance, i. e. below 0.2Ω must be developed. However, few reports have been published on low series resistance diodes for UHF use.
TV Tuners Using Low Loss and Low Distortion GaAs Varactor Diodes
The noise figure of conventional TV varactor tuners is fairly high, when typical Si diodes, whose average resistance is 0.65Ω at 470 MHz, are used. Low noise tuners which comply with FCC noise requirements can be realized if low loss varactor diodes are developed. However, Si diodes with still lower losses can not be manufactured by conventional Si process technology with high production yield. Low noise Si rf transistors with a noise figure of 1.3 dB at 470 MHz is commercially available. However, noise figure improvement using these transistors at 470 MHz is only 1.0 ~ 1.2 dB when compared with conventional tuners. These low noise Si transistors are high in cost and low in production yield because the specification uniformities are insufficient.
Quantitative and qualitative relationship between swirl burner operatingconditions and pulverized coal flame length
Abstract Currently, there are used in power plants two types of burners to combustion the pulverized coal: jet burners and swirl burners. Most of the published works in the field of analysis of burners operating conditions are related to jet burners and are limited to initial region of the flame at the outlet of the burner. For jet burners an offset between the burner outlet and the flame beginning point could be analyzed. In the case of swirl burners with the pre-mixing diffuser chamber an offset between flame ignition point and burner outlet is usually not visible. Because already in the pre-mixing diffuser chamber of swirl burner occurs the ignition of coal-dust together with oxidant-gas cloud and thereby the formation of the flame. Therefore, the analysis of operating conditions for this types of burners requires a different approach. There is a lack of researches, in which will be analyzed changes of the flame length, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. Therefore the aim of this study was to implement and verify the methodology for estimating the flame length, which will allow monitoring changes of operating conditions, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. To carry out the analysis of the image of the coal flame, the two algorithms have been presented. This two algorithms, being based on the video images of the coal flame allows to specify and detect the end point of the flame and on that basis the length of the flame, as well as the fluctuation changes of flame length can be later determined. Both, the change thermal loads of coal burner, streams of secondary air, as well as the constructional change of the angle of swirler assemblies, resulted in distinct changes in the length of the pulverized coal flame.