On 1/10/10 05:18 , Ian Jackson wrote:
In message , D. Peter Maus
writes
On 1/6/10 24:15 , Denny "Smitty" Schmidt wrote:
I am renting a trailer house in Minnesota for the winter. I would
like to
put up a crude longwire. Any ideas regarding the best way to bring the
leadin into the place with out drilling holes? Could I use coax and
close
the window on it without a lot of loss? I have a bunch or RG58 and
RG6 and
some 300ohm flat wire around the place.
Smitty
N0NYW



Closing a window on coax is never a good idea. No matter how thin.
There are, however, other options.

Cable installers in the city, where most of the units are rentals and
transient numbers are high, use a short, flat coax jumper specifically
created for this purpose. Connect your round coax to the flat line on
the outside, then connect another round piece on the inside. Easy
solution. Most of the readily available flat coax jumpers are 75 ohm.
The loss will vary with frequency, but in practical terms for what you
want to do, you'll likely not notice. Universal also has a 50 ohm flat
feedthrough jumper. A better, cheaper solution.

Universal also sells an appliance for this purpose. You set it in the
sill, close the window on it, connect your coaxes, and other lines,
and rock. Made by MFJ. There are two models. Less than $100 for the
more elaborate of the two. You move, you take it with you.

You can also make one. A piece of styrofoam will work. Or any
material, for that matter. Lucite, vinyl, even a scrap piece of
bakelite, or 1 X 2. Cut it to size, drill your holes, run your
feedthrough SO-239, close the window and get after it.


All of these tricks will require special sealing of the coaxial
connectors outside the window. CoaxSeal is exceptional for this. And
special window sealing efforts will be required to keep the Minnesota
winter out of your listening room. It can get brisk in there. But they
work, they leave no mark and they're portable.

One of the more elegant solutions, that doesn't require special
sealing efforts at the window, is to use the window, itself, as a
feedthrough capacitor. Depending on the size of the window (the larger
the better), paint both sides of the glass with an aluminum paint. Or
even cover each side with aluminum foil, tightly attached, and
smoothed. Attach a stub to each side of the glass with a conductive
material. The stuff used for repairing automobile rear window
defoggers is perfect. You can find it in auto supply stores. And some
larger drug or grocery stores in the automotive/tool sections. Once
set and dry, cover that junction with epoxy for sealing and strain
relief. Then attach the center conductor of your coax to the stub on
each side of the glass, and ground each shield. The signal is fed
through the glass as the dielectric of a large capacitor. If the glass
is large enough, and the application is smooth enough, losses are
minimal until you get down into the MW spectrum. When you move, scrape
off the paint, or remove the aluminum foil. No one will ever know you
were there.


OMG. What a meal you are making of this simple problem!

If all you want to do is to bring a wire through an opening window,
simply use insulated wire of a diameter thin enough for the window to be
closed on it without causing serious damage to the wire or the window.
The same goes for a ground wire.


I've used this technique, myself. The reason I didn't mention it,
is that it defeats the noise shielding benefit of the coax at
precisely the point where noise becomes a problem: inside the building.

Computers, routers, printers in the room with the radio will leak
noise into the radio's input at the breach of shield. Retaining
shield integrity becomes a practical consideration.

The flat coaxial jumper is much simpler, and does what you
recommend without breaking the shield, and while retaing
characteristic impedance of the line. The connector still needs to
be sealed with something like CoaxSeal for weatherproofing.

The other options, were just those. Options. For the purpose of
demonstration that there is more than one way to **** a water buffalo.