On 1/7/20 6:27 PM, hwalker wrote:
" ..A 100pF silver mica then gives the attached which indicates 105pF at 7MHz, 109pF at 14MHz and 126pF at 28MHz .."
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The above frequency dependent impedance effects are why manufacturers specify their component values at specific test frequencies. A dedicated LCR instrument, i.e. the well regarded DE-5000, has five test frequencies 100Hz/120Hz/1kHz/10kHz /100kHz one of which will generally match the manufacturers specified test frequency.
???? Also, they choose lower frequencies not only because it's easier to measure at low frequencies, but also because many components suck at higher frequencies, and by specifying low test frequencies, component manufacturers were able to hide the uselessness of their parts.? Several decades ago I had access to an HP network analyzer, and used it to evaluate components for use in the VHF/UHF radio equipment I was designing.? Among standard ceramic chip capacitors, I found that only Murata and Panasonic were suitable for RF designs.? Pretty much everybody else's "capacitors" were much closer to resistors at those frequencies. But at the specified test frequencies of a few kilohertz to **maybe** a few megahertz, they looked fine, and I assume they would work fine, IF you were only designing audio equipment.
Jim Allyn - N7JA