[Antennas] [Antennas]A bit of advice: Use insulated wire...

Sat, 9 Feb 2002 17:00:03 -0600

I would like to know this also. I usually just subtract about 2% for the
insulated wire I also use, but that's not very exact.
Darryl, KK5IB
Using EZNEC 3
----- Original Message -----
From: "Joe Giacobello, K2XX" <[email protected]>
To: <[email protected]>
Cc: "'Antennas Reflector List'" <[email protected]>; "'George, W5YR'"
<[email protected]>; <[email protected]>; "'Don Havlicek'" <[email protected]>
Sent: Saturday, February 09, 2002 8:43 AM
Subject: Re: [Antennas] [Antennas]A bit of advice: Use insulated wire...


> As a follow up to this thread, has anyone figured out a way of obtaining
accurate
> antenna models when using insulated wire?  I would love to build a
multiband quad
> using teflon coated wire in order to minimize icing during the winter.
>
> 73, Joe
>
> Tom Scott wrote:
>
> > Rather than speculate on this issue, it has been very carefully tested
by
> > Rudy Severn in QEX last year (I can supply the article details if you
are
> > interested, it has been reported here before). In summary, it is true
that
> > in most amateur cases, corrosion has fairly little effect on signal
> > radiation (usually less than 1 dB), but it is nevertheless quite
measurable,
> > and there are some cases where the effect can get into the realm of
several
> > dB (depending on antenna configuration). It is also quite demonstrable
that
> > modern insulation with good dielectric characteristics substantially
> > eliminates corrosion and performs measurably better than corroded bare
wire.
> >
> > What Rudy did (VERY clever I thought, and I have personally duplicated
his
> > results), is to create identical coils on a standard form with standard
> > turns and so on and then test the Q at frequency on a Boonton 260A
Q-Meter.
> > My dad just happens to have one of those, so I was able to duplicate his
> > tests on samples similar to his as well as others that I was interested
in.
> > He and I both used high-quality large ceramic coil form to achieve high
Q
> > coils. It can be shown that the Q of a coil is directly proportional to
the
> > series loss resistance of the wire at a given frequency when you hold
the
> > other coil parameters constant. Rudy's data demonstrated that there was
a
> > significant series loss resistance increase in corroded wire compared to
> > un-corroded wire. Since this test is at frequency under completely
> > controlled circumstances, I don't believe there is any reason to doubt
the
> > calculated effect on series loss resistance. The effect was even greater
on
> > stranded wire presumably due to it's greater surface area. I believe
that it
> > is reasonable to assume that this effect is due to the skin effect
forcing
> > some of the current into the partially conducting corrosion. Think of it
as
> > a coating of carbon resistor on the outside of your wire. Since RF is
forced
> > by the interior eddy currents to flow in the outer skin of the wire
(skin
> > effect), this corrosion layer has a much larger effect than it would
have at
> > DC.
> >
> > The other part of the issue is to analyze the impact of an increase in
> > series loss resistance on signal radiation for a given antenna design.
Rudy
> > was concerned because he was designing an antenna (I don't recall the
type
> > now but could look it up) in which the currents were very high at some
nodes
> > which meant that an increase in series loss resistance at those points
would
> > be considerable. This is the case where you can find a several dB loss
of
> > efficiency due to wire corrosion. A simple dipole on the other hand will
> > exhibit very small effect. You can demonstrate for yourself the effect
of an
> > increase in resistance on a given antenna type by simply using a smaller
> > gauge wire on an antenna simulator. My recollection is that corroded
wire is
> > about equivalent to one or two wire sizes smaller (ie: 14ga or 16ga
instead
> > of 12ga).
> >
> > One should of course be very skeptical of any analysis that attempts to
> > measure these kinds of effects by simply reporting results on the air,
or
> > other subjective measures. While it is true that this is what we
ultimately
> > care about, the measurement error inherent in such subjective analysis
> > probably becomes swamped by our personal preconceived expectations. If
> > improvements in receiver design were only made this way, we wouldn't
have
> > made many of the advances in radio design that we have. I am impressed
by
> > the technique that Rudy used because of the objective repeatable nature
of
> > the analysis. I was able to replicate his tests with essentially
identical
> > results.
> >
> > To put all this in perspective, can we operate with corroded wire
antennas
> > without noticeable effect, of course we can. But by the same token would
> > most of us notice the effect of a small sensitivity difference between
one
> > receiver and another? Probably not. But how much do we pay for that last
> > little bit of performance in a run of coax or in the specs of a radio?
> > Within reasonable limits we should properly make all of our system
design
> > choices to optimize performance, knowing that all these choices
cumulatively
> > effect the ultimate performance of our system. Each soldered joint,
isolated
> > feed line, clean connector, etc. may only contribute a little benefit,
but
> > added together, we know they make a difference in our system. Given an
> > informed choice, if I am going to put up an antenna and there is no
impact
> > on cost or other issues, I will choose to use insulated wire. I have no
> > doubt that you may achieve DXCC with bare copperweld or even galvanized
> > fence wire, but there is good data to show that there are better
choices.
> > (Let's see now, where did I put that 12 GA silver plated solid
copperweld
> > with the teflon insulation...?)
> >
> > - Tom Scott, Field Applications Engineering
> > _/_/_/_/_/_/_/_/_/_/_/_/_/
> > Arrow Electronics
> > 9500 SW Nimbus #E
> > Beaverton, OR 97008
> > 503-614-1223 - Office
> > 503-614-0123 - Branch
> > 503-645-0611 - Fax
> > 503-330-6867 - Cell
> > 503-538-5839 - Home
> > KD7DMH
> > _/_/_/_/_/_/_/_/_/_/_/_/_/
> > "The wireless telegraph is not difficult to understand.
> > The ordinary wired telegraph is like a very long cat. You pull on the
tail
> > in New York and it meows in Los Angeles.
> > The wireless is much the same, only without the cat."
> > -- Albert Einstein
> >
> > -----Original Message-----
> > From:   [email protected]
[mailto:[email protected]]
> > On Behalf Of George, W5YR
> > Sent:   Thursday, February 07, 2002 12:50 PM
> > To:     [email protected]
> > Cc:     Lefczik, Larry D; David W Sher; [email protected];
[email protected]
> > Subject:        Re: [Antennas] Need a bit of wire advice
> >
> > Interesting . . .
> >
> > Seems to me, and I think that Mother Nature concurs, that the layer of
bad
> > crud would be no different than a layer of insulation (good crud) on the
> > wire. The current flow will always be on the surface of the lower
> > resistance conducting path which will be the uncorroded copper beneath
the
> > crud.
> >
> > I suspect that a negligible amount of r-f current would try to make its
way
> > through the poorly conducting copper oxide. So, its higher resistance is
> > immaterial. I seriously doubt that any measurable difference in
> > driving-point impedance can be seen between a shiny new copper antenna
when
> > it is first erected and a few weeks or months later when it has built up
> > its layer of crud.
> >
> > Connections, IF made through the crud, would have higher resistance, of
> > course. But all r-f connections to the antenna will sensibly be made to
> > clean copper with solder so that there is intimate contact between the
> > feeder copper and the antenna copper, even though both may acquire a
layer
> > of crud over time.
> >
> > As to corrosion, many copper wires - antennas and otherwise - have
managed
> > to stay up for years without succumbing to deterioration from copper
oxide.
> > My limited understanding is that the oxide layer actually does insulate
the
> > wire from further corrosion by other agents and acts as a protective
layer.
> > And, that once the oxide layer is formed, its chemical reaction with the
> > copper stops and no further crud develops.
> >
> > Don, I guess we just don't agree on this one . . .
> >
> > 72/73/oo, George W5YR - the Yellow Rose of Texas
> > Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
> > Amateur Radio W5YR, in the 56th year and it just keeps getting better!
> > QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
> > Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437
> >
> > All outgoing email virus-checked by Norton Anti-Virus 2002
> >
> > Don Havlicek wrote:
> > >
> > > The 'built-up crud' is oxidation.
> > > Copper Oxide and/or copper sulfate [IF sulfur is absorbed from the
> > > atmosphere], are both corrosive and have higher resistance to electron
> > > flow .. at DC or RF.  Connections with 'crud' will be higher
resistance
> > > .. affecting the impedance of the antenna.
> > > Don
> > > N8DE
> >
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> >
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