Topband: coil wire oxidation

[David Gilbert]

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