Ladder Line Glass Capacitive Coupled Feed Thru

[aa5wg]

Has anyone tried capacitive coupling thru a glass window with ladder line?  There would be no direct connection of the feed line thru the glass into the shack.

I remember seeing this done with 2 meter whip antennas on car windows.

Chuck

[kb3ouk]

I remember an article in QST once about somebody doing the same thing with a longwire antenna on a ship, they couldn't drill holes so it was capacitively coupled through the glass. I think the plates of the capacitor have to be a lot bigger to work at HF than the ones on those 2 meter antennas are.

[W7TFO]

Maybe it will work OK, but in my experience window glass is a really crappy dielectric.

I built a big Tesla coil back in my high school physics class, using 1/2" plate from old bank doors.  36" square.

Punctures and cracks would happen after 30 minutes' run time.

It got 36" sparks easy, made it tough to run in a classroom.

73DG

[kb3ouk]

Just thought of something, most house windows are double pane, car windows are only a single piece of glass, so that might also make a difference, since not only do you have glass as a dielectric, but you also have air between the two pieces of glass too.

[aa5wg]

KB3OUK,

Very good point.  Scratch this idea.

Chuck

[WD8KDG]

Strange how it is just OKIE DOKIE to drill a hole through the side of a house for a phone line or cable TV, but don't dare drill a hole or two for ham radio

Gotta please the little lady of the house (pleasure unit)!!

So if'en you get permission, use a ceramic feed thru insulator (2 for OWL). Get some all thread from the hardware store and some thick PVC toobing. One half of said feed thru insulator on outside of house.....use nuf all thread to pass thru the wall........PVC toobing for electrical insulation.........other half of feed thru insulator on inside of said house. Worried bout electrical breakdown voltage of PVC................McMaster Carr sells hollow ceramic rods.

Craig,

[KB2WIG]

' McMaster Carr sells hollow ceramic rods."

Maybee you can find an `Lectrician who has a few 'nob and tube' tubes.


klc

[W1ATR]

' McMaster Carr sells hollow ceramic rods."

Maybee you can find an `Lectrician who has a few 'nob and tube' tubes.


klc

Look at the old 3/8" black iron for gas lights. Nice.

I lived in a pretty old house a long time ago that had gas lights in every room that were still in working condition. No power in the winter, no problem with heat, hot water, and lights. All without a genny.

[KA0HCP]

I saw an article in QST from the 1930's (?) about making a capacitive link through window glass.  nothing fancy, as I recall it consisted of tin/aluminum foil squares glued to each side of the window pane.

Not a great idea in my opinion.

[K1JJ]

I was curious if this could really be done and give reasonable capacitance. (Myth-buster time)

Using a capacitance plate calculator:
http://www.daycounter.com/Calculators/Plate-Capacitor-Calculator.phtml

I used the dielectric constant average between glass and Plexiglas (about 4)  and used a 1/16" thick glass plate.   1/8" glass might be more reality, but would give less C.

Using  9" square plates (81 sq inches per plate) we get about 1165 pf, which is OK on 3.8 MHz for a 400 ohm match or higher.   A pair of 9" plates on the window might not get XYL approved, however.

If the match is lower impedance, then the plates would need to be bigger.  If we needed .01 uf for a low impedance feed, just to show how ridiculous the plate size gets: Using 0.125 glass thickness, die constant =4, the plates become 36" square. (1296 sq inches per plate )


Myth-buster opinion?  Plates plausible, but not practical for the lower bands, especially for low impedance feeds.  Higher bands - might be a good solution if we cannot drill holes.

T

[kb3ouk]

Wonder if there would be any risk of the two plates that are beside each other arcing over between each other?

[K1JJ]

Wonder if there would be any risk of the two plates that are beside each other arcing over between each other?

The distance apart will be no different than when using conventional openwire.

Arcing distance will depend on the power used, impedance at the particular point and moisture/ dust, etc.

However, spacing the plate edges 4" apart should be a reasonable minimum distance for most applications. Or just mimic the spacing of the openwire used.

T

[KB2WIG]

" Look at the old 3/8" black iron for gas lights. Nice."

Well, gaslite can scare you.... My earlobe touched a feed one time, scared the crap out of me as I was clipping some dead wire.

klc

[Opcom]

' McMaster Carr sells hollow ceramic rods."

Maybee you can find an `Lectrician who has a few 'nob and tube' tubes.


klc

oh yeah those tubes! Always pick 'em up at flea markets in the junk bins. 25 cents 50 cents Those are like gold for running Hv through walls or paneling. And they are not plastic, and are made in the USA.