[TowerTalk] question on copper wire used for hairpins and

[Jim Thomson]

Date: Thu, 13 Oct 2016 18:22:16 -0700
From: David Gilbert <xdavid at cis-broadband.com>
To: towertalk at 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