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i just ran a check with the sound card:
a) the sound card contributes noise. i shoved in a 50 ohms resistor into the mic input, cranked up the mic level, save a 'silent' wave file and saw it through a hex editor. There is a random noise of about 2-3 bits. That means, the effective range is not 16 bits but 12 bits. 12 bits can represent 4096-1 as the highest number. That means, the dynamic range is 4096 squared: about 16 million or 72db. A little low really for interesting work. there isnt enough 'roof' to resolve a spur about 60db down without touching the grass b)the sampling is at 44khz. some of the posts got confused between 20khz b/w and 20khz sampling rate. hans is right about the PC being a kludge when compared to an oscilloscope. I live in India and second-hand oscilloscopes are a rarity. The new ones cost an engineer's whole year's salary. I have purchased a tektronix 454 last month on ebay for $300, it is still on its way to India. So, while i can imagine that in a number of more developed countries oscilloscopes are not really a problem, they do remain a problem in many parts of the world. More often than not, an amateur already has a PC. Adding a simple hardware to be able to do quick and dirty spectrum analysis might be an interesting option. As Wes writes in SSD and EMRFD, the purpose of test instruments is to help with the projects on hand, rather than be projects themselves (then he went on to homebrewing a spectrum analyser, hehe). - farhan |
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