[AMPS] clear coating conductors

[Skip S Isaham]

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.  


___________________________________________________________________
Get the Internet just the way you want it.
Free software, free e-mail, and free Internet access for a month!
Try Juno Web: http://dl.www.juno.com/dynoget/tagj.

--
FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm