Date: Thu, 13 Oct 2016 18:22:16 -0700
From: David Gilbert <xdavid@cis-broadband.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] question on copper wire used for hairpins and
the like...
Hi, Gary.
According to some online skin effect calculators I found, and assuming
that the hairpin is something on the order of 4 gauge wire, the current
at 4 MHz reaches an equivalent depth of 1.4 mils or so. It is of course
a logarithmic current density profile, but the equivalent uniform
density depth is around 1.4 mils. I doubt that the tarnish is anywhere
near that thick.
73 and good to that you're still plugging away on your new station,
Dave AB7E
On 10/13/2016 2:05 PM, StellarCAT wrote:
> So ... Force12 used (uses!) bare copper wire as their hairpins. I have a
> 80/75 rotary dipole that has a hairpin made from bare #10 wire ... it is now
> 11 years old and it looks dull ? tarnished ... not corroded at all ? just the
> dull brown color that copper gets to be ... is there any reason why that
> can?t be reused (I?m putting it back up)? I realize the skin effect will mean
> that only the outside such-n-such micrometers are used for conductance ...
> but would any resistance in the ?tarnish? factor in or would it appear to be
> the same today as it was when brand new?
>
> My guess is the answer is yes ? it can be reused and it would continue to
> work as if it were brand new ... and my one point of argument towards that
> fact is that when it was up ? for 7 years ? there was no apparent change in
> the operation of the antenna! The SWR didn?t change, which is what the
> hairpin would most drastically effect ... the 2:1 bandwidth didn?t change
> noticeably (Q) ...
>
> thoughts and discussions...
>
> Gary
> K9RX
### Dull and tarnished has zero effect. Its the connections on each end that
you have to worry about. The rf current simply travels beneath the tarnish.
As long as the connections on each end are good, you are good to go. In most
cases, F12
terminated the helical hairpin coils with crimped and soldered lugs...so the
end terminations are not an issue. There is one heckuva lot of current in
the hairpin though. Id use something bigger, like 8 ga bare cu or 8 ga magnet
wire, or .187 or .250
cu tubing, with the ends flattened.... then punch /drill .187 holes to handle
the 10-32 / 10-24 SS machine screws they used.
Jim VE7RF
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