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#11
June 20th 06, 07:25 PM
posted to rec.radio.amateur.antenna
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Copper tubing capacitors
Roy Lewallen wrote: K7ITM wrote: wrote: I guess I'm learning a public lesson but I'm going to post this as a wrapup. I figured out the problem. My inch of wire appears to measure about 0.06 microhenries. 1/(2*Pi*sqrt(0.06microhenries*165picofarads) ~ 50MHz 73, Dan N3OX Yeah, you discovered why they* suggest using an array of values of bypass capacitors, even when using SMT capacitors with "zero" lead length, to do a good job of bypassing a supply over a wide frequency range. And why even in ham construction literature from the 1950s they talk about keeping leads very short for good RF construction. . . . And just one of the many reasons I keep saying that good RF measurements are much more difficult to make than most people realize. Roy Lewallen, W7EL As one who is dedicated to making equipment that enables making good RF measurements, I say, "Amen, Brother Roy." One of the problems, if you will, of modern test equipment is that it makes it LOOK like it's easy to make good measurements, but you would be wise indeed to think instead that the equipment operation is easier so that you can spend your time making sure that your measurement setup is appropriate to the task, and so that you can make measurements in multiple different ways as a double-check or triple-check with less effort than you might have used before to make one uncertain measurement. Only slight topic drift: it's rather like trusting SPICE (or other simulator) to give you the right answer without understanding either SPICE's limitations or your model's limitations. Properly used, SPICE is a great tool. Improperly used, it will give you some very bad answers. Neither SPICE nor modern test equipment is a substitute for using your head--but both can free you to use your head more effectively and creatively. Cheers, Tom |
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