On Sun, 18 Jan 2015 13:00:01 -0700, Irv Finkleman VE6BP
wrote:

I intend to order the MFJ-1780 Box Fan Portable Loop.
I'd have it on order already but they are closed on the weekend.

You can view an image at
https://farm4.staticflickr.com/3913/...596a70d0_d.jpg

http://www.mfjenterprises.com/Product.php?productid=MFJ-1780
You're going to pay $330 for that? Surely you can find a cheaper mag
loop antenna?

One chap has had his hanging in a tree, with weather
protection provided by a plastic garbage bag.

Great idea. However, the reason is not so obvious. See below.

This antenna was obviously not designed for permanent outdoor
installation. It says so in the manual:
http://www.mfjenterprises.com/Downloads/index.php?productid=MFJ-1780&filename=MFJ-1780.pdf&company=mfj
OUTDOOR USE
Note : The MFJ Box Fan Loop can
be used outdoor only in good
weather conditions ( not in windy or
stormy weather).

Mounted horizontally any water that collects inside will end up on the
insulated side plates, where the water will not do any major damage.
However, mounted vertically puts the plates of the tuning capacitor in
a horizontal position, where they can collect water. This is bad. If
you want to hang it vertically, please mount it with the capacitor
plates vertical. This is NOT the ideal position for vertical
polarization, so there may be some signal loss. Also, drill some weep
holes in the bottom of the box so that water will drain out.

The trash bag cover has a unique advantage. The black low-density
polyethylene (LDPE) trash bags are transparent to long wave infra-red
radiation, also known as heat. Hang a trashbag full of water in the
sun, and it will soon deliver hot or warm water. That's how these
work:
http://www.coleman.com/product/5-gallon-camp-shower/2000014865?contextCategory=28170
If some water gets into the bag (e.g. condensation) and lands on the
tuner, as soon as the sun comes out, the bag will get hot enough to
evaporate the water. Be sure to leave the bottom of the trash bag
partly open, so the water vapor has a way to get out of the bag. Even
in the dim light of dawn, there will be enough heat to prevent the
temperature from staying below the dew point (unless it's really
cold). I don't know exactly which style or thickness of garbage bag
to use. My guess is as thin as possible and only one layer, so that
the most IR gets into the bag.

If you want to lube the capacitor bushings or bearing, just use some
heavy waterproof grease. I tend to use lithium white grease for
everything, but almost any other grease will work. Since you're
pushing RF through the grease, I guess dielectric grease might be a
better choice. Forget about WD40.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558