Practical Line Filters

Helps spread non-symmetric noise equally onto both lines (in effect not really an X-cap) 

This may be an actual air gap (between split core halves), or it may be a distributed gap, as in powdered iron cores. Though this lowers the inductance index (Al) somewhat, the resulting solution is much more immune to production variations, and is also more stable over time. In general, whenever we introduce an air gap, the core starts partially acquiring the properties of the interposing air — and since air never saturates, the air-gapped core too has a much softer saturation characteristic. 

This can be confirmed by simply pressing the tips of an ohmmeter at two points on the surface of any bare ferrite lying around in the lab. Further, if we are trying to rely on the enamel coating of a typical copper magnet wire to protect from shorts, we should know that the coating is considered to be just operational/functional insulation, and is not considered to be even basic insulation. 

We can also consider paralleling a larger value Y-cap with a small Y-cap. 

Capacitance (pF) Resonant Frequency (MFiz) Capacitance ( xF) Resonant Frequency (MHz) 

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Figure 10-1 Practical Line Filter and the CM and DM Equivalent Circuits...

Guard columns and in-line filters alone will not ensure long life for the analytical column. They are designed to perform a specific function for a finite period of time. They, too, will be short-lived if shortcuts are taken in sample preparation and mobile phase quality control. Use of a guard column does not mean that other good analytical practices can be neglected. Shortcuts mean shorter life for any column. 

The thicker the filter the lower the ratio of intensity of KP to Kot, in the transmitted beam. But filtration is never perfect, of course, no matter how thick the filter, and one must compromise between reasonable suppression of the KP component and the inevitable weakening of the Kot. component which accompanies it. In practice it is found that a reduction in the intensity of the Kot line to about half its original value will decrease the ratio of intensity of KP to Kot from about in the incident beam to about in tbe transmitted beam this level is sufficiently low for most purposes. Table 1-1 shows the filters used in conjunction with the common target metals, the thicknesses required, and the transmission factors for the Kot line. Filter materials are usually used in the form of thin foils. If it is not... 

Pulse compression requires a separate matched filter be supported for each waveform used by the radar system. In practice, this filter is implemented via fast convolution as illustrated in Fig. 17.12. From Fourier transform theory, frequency-domain multiplication is equivalent to time-domain convolution. Hence, receiver digitized output data is input to a FFT, multiplied by the Fourier transform of the matched filter response, and then passed through an inverse FFT (I FFT) to output time-domain data. The matched filter reference functions transforms are generally computed off-line and stored in memory to support real-time processing. Fast convolution significantly reduces the number of operations required compared to time-domain direct convolution of returns and the appropriate matched filter function. 

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