In article ,
Jeff Liebermann wrote:

Paranoia. See:
http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm
There's quite a bit of useful info on building magnetic loops. One
interesting comment was:
UPDATE 24-Feb-2012: one and a half year after construction,
I have used a professional milliohm meter (HP 4328A) to measure
the DC-resistance of the copper parts of my loop (i.e., octagon
+ wires to the clamps): 3.2 milliohm. I also measured the resistance
of a brand new round loop - without solder joints: also 3.2
milliohms. My joints are pretty good! However: I measured a
DC-resistance of over 4 milliohm between the copper wires and
the stainless steel clamps (i.e., 2 x 4 milliohms total). This
kills the efficiency of the antenna - which I had already noticed
over time. Must use a different method in my next design!

I've seen the same thing with a loop I built (using an ESR meter to
measure resistance). The DC resistance of mating parts is the same
whether it's soldered, or just stuck together. In other words, the
loop resistance doesn't change with soldering.

So, what does the soldering do? One possibility is that it helps
produce an unbroken surface area, which is useful when all the RF
conduction is via skin effect. Unless there's some kind of dramatic
change in element diameter, I don't see skin effect as a problem
worthy of soldering.

In short, all soldering and welding does is add some desperately
needed mechanical rigidity.

If a loop made from tubing and junctions is just "stuck together", it
may have the same resistance as a one-piece loop initially. The
tubing-to-joint connections typically involve enough scraping (an
interference fit) to create a fresh metal-to-metal junction... nice
low resistance.

I strongly doubt that it'd remain so, after a year or so of exposure
to air (and water and sun). Oxygen is going to infiltrate those
contact surfaces and oxidize the metal; any sulphur vapor in the air
will attack the surfaces as well. The quality of the connection will
deteriorate and the resistance will climb.

(Audiophiles who know their stuff will unplug and replug their signal
cables periodically, to "wipe" the contact surfaces free of oxide
and create a clean connection once again... RCA connectors are
quite awful and this is one of their failure modes. An unplug/replug
is far cheaper than buying the latest new overpriced "magic" cables
at the boutique audio store, and works just as well!)

I've seen plenty of antennas fail due to oxidizing and corroding
connections. We had to completely rebuild the grounding-and-radials
base of a Hustler G7-144 when the original interference-fit
connections deteriorated after a decade up in the sun.

A big benefit to soldering the joints, is that you'll seal the metal
contact regions away from oxygen, and fill the gaps with a metal which
is also a reasonably good conductor. Even if oxygen starts affecting
the outer surface of the tube, there will still be solid metal beneath
it.

A similar problem with oxidation affects screwed-together "American
Legion" J-pole antennas... they start generating intermod interference
and broadband hash when transmitting. A dab of TIG-weld bead to bond
the elements to the base eliminates the problem.

You might get some of the same benefit by using an antioxidant paste
on the joints when connecting them, but it wouldn't provide quite the
same protection, and it wouldn't provide the mechanical strength you
quite rightly point to as a benefit.