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measuring cable loss
On Tue, 14 Aug 2007 00:14:31 -0700, K7ITM wrote:
On Aug 13, 10:56 pm, Richard Clark wrote: On Mon, 13 Aug 2007 13:09:09 -0700, Jim Lux wrote: Or, something like a 50k resistor into a 50 ohm load will be about 60 dB down, Hi Jim, Unlikely. With parasitic capacitance at a meager 1pF across the 50K, its Z at 10MHz would compromise the attenuation presenting closer to 50 dB down. At 1Ghz it would plunge like a rock. This, of course, presumes a 1/4 watt resistor. A better solution is to use surface mount resistors where the parasitics are down at 100aF - but then you will have a frequency dependant divider unless you can guarantee that the parasitic capacitance of the 50 Ohm resistor is 100pF (sort of casts us back into using a 1/4 watt resistor with a padding cap). At 1GHz, it is not going to look like a trivial 50K load anymore. 100aF??? :-) X(100aF)/X(100pF) = 50k/50 ??? ;-) ;-) S/B 100fF (trying to watch the Perseids and do math at the same time). |
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