At 06:58 AM 8/28/2007, Dan Zimmerman N3OX wrote:
>Has anyone measured corroded copper inductor Q vs. shiny new copper at
>HF frequencies?
>
>Specifically, I wonder if there'd be any practical benefit to
>polishing and coating a 3/4" copper pipe transmitting magnetic loop
>with coil varnish?
>
>The capacitor is a Jennings vacuum variable and the silver-plated cap
>clamps have been soldered to the loop using solid silver plated copper
>strap, so I don't have a particularly lossy capacitor arrangement.
>
>I also know that shiny new copper vs. shiny new silver wouldn't make
>much difference. What I don't know is the conductivity penalty of
>corroded copper.
I would venture to guess that it's hard to come up with a single
number. Copper Oxide is a semiconductor with fairly high resistivity
(it's been used in static dissipative films, for instance, and in
rectifiers). Who's even to say that the corrosion is copper oxide, or
for that matter, which of the two kinds of copper oxide it is.
If the high resistance stuff is on the surface, then the current
probably won't flow through it, so the loss isn't that high.
In your case, the surface might not be all that big a deal, it would
be corrosion in a connector, where the copper oxide/sulfide/etc is
directly in series with the high current path.
>The loop is just a fun experiment since I had the capacitor burning a
>hole in my junkbox but I'm interested in seeing how well I can get it
>to work vs. my larger antennas.
Build it and try.. empiricism is king.
Jim, W6RMK
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