Peter Burbank wrote:
>
> I poked around on the net awhile to see if Silver Sulfide was an
> insulator but never did find anything.
> 73 Pete NV4V
>
I came across the reference below from
http://www.g3ynh.info/zdocs/comps/refs.html (about one fourth of the way
down the page):
"Re: Communication from Roy Lewallen, W7EL, which was as follows: AgS
has a resistivity of 1.5 - 2.0Wm, and is believed to be the most common
silver tarnish. Cu2O is 10 - 50Wm, CuO is 6KWm, CuS is 0.3 - 83mWm
(source: 1993 CRC Handbook of Chemistry and Physics)."
The entire skin effect chapter by G3YNH (
http://www.g3ynh.info/zdocs/comps/part_1.html ) looks interesting, by
the way, and points out that the magnetic permeability of a material has
significant effect on it's skin effect depth, and therefore its skin
effect losses. Resistivity alone determines contact loss, but Q of the
coil itself is a very complex matter involving both resistivity and
permeability of (in this case) the sulphide layer.
"If the coating is a perfect insulator or a perfect conductor it causes
no loss. Loss is a maximum at some intermediate value, which depends on
frequency, layer thickness and base material - not a trivial calculation."
The chapter also includes this rather humorous comment:
"The surprise is perhaps that the current-carrying layer is extremely
thin even at low frequencies; the skin-depth in copper (for example)
being only 48mm (0.048mm) at 1.9MHz. Notice also that the ferromagnetism
of iron has a devastating effect on the skin-depth, even though iron is
a material of relatively low conductivity. A recent recommendation in a
British Amateur-Radio magazine, that plastic-covered iron wire sold in
Garden Centres can be used to make aerials, does not seem so sensible in
light of these calculations. <snip> For truly dire performance ...
soft-iron garden-wire is in a class of its own (although
/galvanised/-iron fencing wire is not too bad, except that it will
eventually rust). A 10m long transmission-line made from plain iron wire
(1.5mm diameter) would have a loss-resistance in the region of 140W at
14MHz. The only saving grace is that the author of the recommendation
that it can be used to make antennas will be hampered in passing-on his
ideas via radio."
Dave AB7E
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