re: coating of conductors
I've had two past experiences which make be believe coating certain
conductor application are a bad practice.
1) The first project was a simple 2 element yagi for 52.525MHz.
The unit preformed well using a standard gamma match to 50
ohm coax. Upon completion and final testing of the yagi, I
decided to spray the gamma with urethane for moisture prevention.
The impedance of the gamma changed radically. Tests with
the basic instruments I owned at the time proved the coated
gamma was the problem. I tried to remove the coating
with various chemicals, but I was never able to restore
that network to a usable form. I made a duplicate gamma
(less the coating) and the beam went into service for
many years.
2) While working with VHF and UHF cavity construction, I cleaned
some modified copper metal parts. A friend coated the materials
with a clear coat and a similar problems as described above
occurred. Paint stripper was used in masse to eliminate the
coating and the correct circuit response returned to our projects.
sidebar:
I do endorse copper silver plating when possible, mostly for the
measurable increase in Q at higher frequencies and the
tendency of copper to oxidate in many non sterile applications
where amplifiers are known to frequent.
I can clearly see the difference in two identical UHF cavities (one
silver
plated, one not) on my HP 8920a. Next time I'm in the construction
and tune mode, I'll record my observations of the difference.
The silver plating issue now revolves around the availability
of cost effective silver plating facilities. Environmental concerns
and the State of California have put many smaller plants
out of business. Larger plants don't often enjoy
one-off small projects.
cheers
skipp wv6f
[snip]
>What do I do? I don't plate anything. I try to use soft copper when I
can.
>Polish it up and spray it with Krylon or Urethane .........
:As do I, Larry.
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