Figure 1: Printing a weather chart while underway, somewhere in the Pacific (1988) Introduction Those who regularly read my technical articles may recognize the first theme I want to address — the rapid convergence of mathematics and everyday reality. In the pre-computer days of electronic technology, one would use mathematics to plan a project, then build and test a system that represented an approximate embodiment of the original math. For example, in the 1970s when I designed Space Shuttle electronics, the final flight hardware always reflected the intent of the original mathematics, but the distance between theory and practice was often large. Now that computer methods have taken hold, in radio receiver and signal processor designs we're witnessing a rapid convergence of principles and practice. Paket 4g landing_page usim replacement kartu 3. One reason is the gradual replacement of analog with digital circuits, another factor is the degree to which microprocessors now create in software what had once required explicit, single-purpose circuits. Because of the low cost and high speed of modern microprocessors, it no longer makes sense to consider most analog designs, and it's becoming practical to write signal processing code directly in software. One of my recent projects is a software-based receiver/processor of slow-scan video images of nautical weather charts transmitted over the shortwave bands (a project named ). I have always needed weather charts, dating back to my and extending to the present, for my. ![]() Sep 15, 2010 There is a chance that none of these PLLs will work for your comp, in this case im sorry but you are unable to use clockgen to OC. If this has helped you at. CLKIN1 signal. The dynamic reconfiguration inputs and outputs of the PLL_ADV primitive are hidden or terminated within the PLL module, as is the control input for the PMCD mode. All other inputs and outputs of the PLL_ADV primitive are inputs and outputs of the PLL module. In years past I used a demodulator box to decode shortwave weatherfax transmissions and print the result on paper (see Figure 1), but I recently realized that, because of great speed improvements, a modern laptop with a sound card should be able to perform the entire task in software, thus eliminating a single-purpose black box. Figure 2: Phase-locked loop block diagram In the weatherfax project, one of the key design issues was to convert a range of audio tones into a video signal, essentially FM detection. During a lengthy design and testing phase I evaluated most known methods for FM demodulation, beginning with a crude method that counted clock cycles between zero crossings, then a system of bandpass filters, and finally I designed a phase-locked loop detector. The phase-locked loop approach turned out to be vastly superior to the other methods, to the degree that I want to describe the method in detail, so others won't pass up this terrific approach. I'll have more to say about the at the end of this article, but first let's discuss phase-locked loops. At its most basic, a phase-locked loop (hereafter PLL) compares the frequency of a local reference oscillator to that of a received signal, and uses a feedback scheme to lock the local oscillator's frequency to the incoming signal (see Figure 2). At this point, one application for a PLL should be obvious — the oscillator control signal's amplitude is proportional to the difference between the incoming signal's frequency and the local oscillator's free-running frequency, therefore it represents demodulated FM. But unlike typical FM detectors and with reasonable care in PLL design, the oscillator control signal can be a near-perfect duplicate of the original modulating signal, suitable for high-fidelity music, scientific telemetry, video, and other demanding requirements. PLLs are very good FM detectors, but by changing feedback parameters, they can also detect very weak signals buried in noise — indeed a PLL is the preferred approach for detecting weak signals, as from a deep space probe. For this application the loop low-pass filter (Figure 2, green) is adjusted to allow through only a very small bandwidth (to reject noise) and the reference oscillator is tuned to the expected signal frequency.
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