measures wrote:
>Ian wrote:
>>...... Pure copper actually has a higher conductivity than silver,
>
>? Not when I took Physics of Electricity, Ian. . . According to
>Frederick Terman, at 20-degrees C, silver has a resistance of 1.629
>u-ohm per cm^3. Copper has a resistance of 1.724 u-ohm per cm^3.
>
You're right, Rich - but only for the pure materials.
Unfortunately even "pure" doesn't cover it: there's a difference in
resistivity between pure hard-drawn and pure soft-drawn copper owing to
the crystal structure, and likewise pure silver has different crystal
structures and resistivity depending on how it's made and prepared.
While it's possible to measure the resistivity very accurately, it isn't
possible for us amateurs to know which grade of copper or silver we're
dealing with. Taking all the variables into account, "about the same" is
perhaps more accurate of all.
However, a few years ago somebody from Australia made some postings to
rec.radio.amateur.homebrew(?) about professional work he had done
several years before that, in which he found that commercially available
silver plating had a *higher* RF resistivity than clean bare copper.
BTW, the units of resistivity are ohm-cm (that's cm^2 of cross-sectional
area on the top line of the fraction, divided by cm of conductor
length).
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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