[Lowfer] Some snow coils

Thu, 13 Feb 2003 21:05:29 -0600

That old plastic insulated building wire basket wound coil still works today
at the bottom of the "WE" vertical thanks to Lyle. It has made a 1304-mile
reception possible this winter. Still working and will be for many more
years to come. Thanks again Lyle.

Mike>WE0H
http://www.we0h.us/lf
WE 185.3026kc
QRSS 30 & -.-.  .--
Vertical tonight

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Lyle Koehler
Sent: Thursday, February 13, 2003 8:39 PM
To: [email protected]
Subject: Re: [Lowfer] Some snow coils

In response to Bill A's questions, I have several objections to mounting the
coil inside the building.

1) I believe it was Bill who pointed out that, if you consider the coil and
associated leads as part of the 15 meter allowable length, the useful length
of the antenna is reduced. I'm assuming that the inside wires don't radiate
because they are shielded by the metal building. With a big coil that has to
be mounted 2 or 3 feet below the roof, you can lose quite a bit of effective
length.

2) Wet snow buildup on the roof around the antenna lead will cause a
significant increase in losses if the loading coil is inside the building.
At that point, the impedance can easily be hundreds of thousands of ohms.
For example, 3000 ohms of reactance with a system Q of 100 = 300,000 ohms.
On the transmitter side of the coil, the impedance is 3000/100 = 30 ohms,
and a foot of wet snow around that part of the wiring would have little
effect. A pile of wet snow on top of an external, elevated coil will
introduce some losses and detuning, but it isn't as severe because the snow
is electrically "floating".

3) It's a lot more work to install a big insulating "window" in the roof
than to put in a small feedthrough. In my case, there is an SO-239 connector
mounted in a 5/8 inch hole in the metal roofing. A little dab of silicone
bathtub sealer around the connector, and the job is done, without
compromising the integrity of the roof. Actually there are some translucent
fiberglass skylights in the roof fairly close to the location of my
feedthrough, so I could have gone that route if I wanted to. However, if it
had been convenient to do so, I would have hung the loading coil 20 feet
above the roof rather than 5 feet. That would improve the current
distribution in the antenna and might reduce the losses from things like the
row of arbor vitae "shrubs" that have grown way above the roofline along one
side of my garage.

My present Litz-wire loading coil is small enough to fit inside a 5-gallon
polyethylene bucket which protects it from the weather. Unless it gets hit
by lightning, it will probably last a lot longer than I will. Earlier I was
using a much larger basket-wound coil of #14 plastic insulated building
wire. It was originally protected by a plastic bag, which lasted about a
week before the wind ripped it to shreds. After that, if the coil iced up,
it stayed that way until the next thaw. That was back when I considered it a
successful season if my beacon was heard more than half a dozen times :-)
After about 6 years the plastic insulation on the wires became severely
weathered and I suspected that the losses were increasing. However, there
was no significant improvement in antenna current when the old coil was
replaced with the Litz coil (Q of 600 or 700).

Lyle