through glass coax coupling
 

"Haines Brown" wrote in message
...
Wimpie writes:

Why not using inductive coupling? You can get reasonable coupling as
wires are just mm away from eachother, so you don't need high Q factor
circuit.

Didn't occur to me. Are you suggesting a couple coils sharing an axis,
one just inside the window and the other outside? Would the two coils
simply be designed for a 50-ohm impedance at, say, 10 meters?

I can imagine wrapping a 50-ohm coil on pvc, and inserting it into a
larger diameter pvc that is capped and which has a coax connector passing
through it. and the whole attached to the glass with silicone
adhesive. One on either side of the glass.

Matching indoor only is possible (so you don't need matching outside
to interface to 50 Ohm coaxial cable).

Not sure of your point. It seems I need to match outside.

Another problem just occurred to me. I'll use a MFJ magnetic loop, and
its tuner, if I recall, depends on an uninterrupted electical connection
through the coax. If so, I'm stuck.
--

Haines Brown, KB1GRM

Haines,

Just read the other postings about inductive coupling and I think that would
be the best way to go with a standard wire antenna like a half wave dipole,
vertical, etc.

I can't see any way of getting a magnetic loop antenna to work because you
need a direct DC path for power and tuning commands from the tuning unit to
the loop.

Might be better to put your ingenuity to better use by finding somewhere
hidden to run a thin bit of coax through the wall. Behind a switch plate,
power socket, joint fillet, alongside a pipe. There must be somewhere to put
a 1/4 inch hole that can be concealed later? For QRP work, you might get
away with a short through wall length of really thin coax, the 1/8 inch
stuff used to connect signal assemblies inside equipment.

If you are really brave, a masonry drill at high speed will cut through
glass with a bit of soapy water acting as a lubricant. Take your time and
try and brace the other side with a wooden block or elses a big bullseye
chip will be thrown out when the drill breaks through. Fill the hole with
transparent quick set epoxy when it is no longer needed.

Mike G0ULI

through glass coax coupling
 

Mike Kaliski wrote:

Haines,

The versions I used years ago relied purely on capacitive coupling. The
braid was broken and only the centre lead of the coax was connected to
the plates. The earth return was via the automobile chassis for vehicle
use, or via earth connections for domestic use. The metal frame of the
window might work if you have any means of getting a good connection,
otherwise you will need some form of reliable (low impedence) earth
connection inside and outside the building for the system to work properly.

The coupling through the glass should be purely capacitive although some
inductance effects will inevitably be introduced due to the size of the
plates.

You'll have a considerable amount of inductance for another reason if
you follow this approach.

Consider what happens when you separate the two conductors of the coax
as Mike suggests. One conductor continues more-or-less directly through
the glass. The other conductor becomes the "ground" path from wherever
the current leaves the inside of the coax shield on one side of the
glass to where it again enters on the other side. These are the two
conductors of a transmission line which you've inserted in series with
your normal line. If you'll do a little rough calculating, you'll find
that this line has a much higher impedance than 50 ohms. So, if
electrically short, its effect will be that of a series inductance. If
it's not so short, the impedance transformation will be a lot more
interesting. Another thing that happens is that the length of the
"ground" conductor is greater than the length of the center conductor.
This will probably give rise to common mode currents, which will involve
the outside of the coax in the active feedline.

As an alternative you might consider making up two matched tuned
circuits (coil and capacitor) set for the 10 metre band and try
inductively coupling the coils through the glass. To my mind that would
be smaller and easier to set up without the need to worry about earth
feeds. A kind of through glass balun if you like. Obviously you will
need to keep a reasonable distance away from the metal window frame, but
a couple of turns of wire and a couple of capacitors may be all you need.

That might have a better chance of producing a smaller disturbance to
the whole feed system. If you use direct capacitive coupling through the
glass, however, you should remember that you have two conductors to deal
with -- calling one "ground" doesn't give it magic properties. I'd use
two coupling plates, one for each conductor, as close together as
possible. A bit of intentional shunt capacitance would help compensate
for the inevitable series inductance which would be created by even that
setup.

Roy Lewallen, W7EL

through glass coax coupling
 

I was hoping to see a commercial coupler to figure out how they are
constructed, but so far have seen only one for XP radio, and it is not
clear what's up with it.

If by commercial couplers you mean the units for through glass antennas,
then the ones that I have taken apart consisted of a parallel tuned circuit
with the coax inner tapped a little way up the coil and the braid connected
to the cold end of the coil. The 'hot' end of the tuned circuit was
connected to the coupling plate. The antenna just had a coupling plate. Of
course it worked by virtue of the approx 1/2 wave whip having a high
impedance at the base, so the required value of coupling capacitance was not
extremely high.

73
Jeff

through glass coax coupling
 

"Roy Lewallen" wrote in message
news:TJ-dnV1WvLdVMWjanZ2dnUVZ_r6rnZ2d@easystreetonline...
Mike Kaliski wrote:

Haines,

The versions I used years ago relied purely on capacitive coupling. The
braid was broken and only the centre lead of the coax was connected to
the plates. The earth return was via the automobile chassis for vehicle
use, or via earth connections for domestic use. The metal frame of the
window might work if you have any means of getting a good connection,
otherwise you will need some form of reliable (low impedence) earth
connection inside and outside the building for the system to work
properly.

The coupling through the glass should be purely capacitive although some
inductance effects will inevitably be introduced due to the size of the
plates.

You'll have a considerable amount of inductance for another reason if you
follow this approach.

Consider what happens when you separate the two conductors of the coax as
Mike suggests. One conductor continues more-or-less directly through the
glass. The other conductor becomes the "ground" path from wherever the
current leaves the inside of the coax shield on one side of the glass to
where it again enters on the other side. These are the two conductors of a
transmission line which you've inserted in series with your normal line.
If you'll do a little rough calculating, you'll find that this line has a
much higher impedance than 50 ohms. So, if electrically short, its effect
will be that of a series inductance. If it's not so short, the impedance
transformation will be a lot more interesting. Another thing that happens
is that the length of the "ground" conductor is greater than the length of
the center conductor. This will probably give rise to common mode
currents, which will involve the outside of the coax in the active
feedline.

As an alternative you might consider making up two matched tuned circuits
(coil and capacitor) set for the 10 metre band and try inductively
coupling the coils through the glass. To my mind that would be smaller
and easier to set up without the need to worry about earth feeds. A kind
of through glass balun if you like. Obviously you will need to keep a
reasonable distance away from the metal window frame, but a couple of
turns of wire and a couple of capacitors may be all you need.

That might have a better chance of producing a smaller disturbance to the
whole feed system. If you use direct capacitive coupling through the
glass, however, you should remember that you have two conductors to deal
with -- calling one "ground" doesn't give it magic properties. I'd use two
coupling plates, one for each conductor, as close together as possible. A
bit of intentional shunt capacitance would help compensate for the
inevitable series inductance which would be created by even that setup.

Roy Lewallen, W7EL

Roy

Very helpful and useful additional comments as usual. Thank you.

Mike G0ULI

through glass coax coupling
 

"Mike Kaliski" writes:

I can't see any way of getting a magnetic loop antenna to work because
you need a direct DC path for power and tuning commands from the
tuning unit to the loop.

I must apologize for starting a thread that I realized would be for me a
dead end. I've not used a magnetic loop before and so easily forgot
about the need for a direct DC connection. However, the thread was
interesting and hopefully worthwhile.

Might be better to put your ingenuity to better use

Yes. Options are limited because I'm at the eighth story of a steel
high-rise, and the enamled metal outside surface material doesn't lend
itself to drilling. In any case, I don't own it and wouldn't feel right
about destroying property not mine. The window is a casement window, and
I'm now thinking of leaving it permanently ajar and gluing (silicone) on
the inside frame a piece of plexiglass with a coax feedthrough. That way
I can have light from the window, protection from the elements and not
destroy anything. Ultimately it can be removed when necessary.

--

Haines Brown, KB1GRM

through glass coax coupling
 

The window is a casement window, and
I'm now thinking of leaving it permanently ajar and gluing (silicone) on
the inside frame a piece of plexiglass with a coax feedthrough. That way
I can have light from the window, protection from the elements and not
destroy anything. Ultimately it can be removed when necessary.


If you are going to do it this way, I might suggest you use weather
stripping ( for doors, etc. ) instead of Silicone sealer. It comes in a
variety of thicknesses.... should provide a good seal for your slightly
ajar window, easily allow some RG-8X type coax through, and be a lot
easier to remove than the silicone in the future. Also, will still allow
you to open your window if need be ... just a thought.

Ed K7AAT

through glass coax coupling
 

Haines Brown wrote:
... Options are limited because I'm at the eighth story of a steel
high-rise, and the enamled metal outside surface material doesn't lend
itself to drilling. In any case, I don't own it and wouldn't feel
right about destroying property not mine...

Have the window replaced and leave a space at the bottom
of the pane for a plexiglas feed through panel.

When you move, have the window replaced again.

Couple hundred bucks, it's done right, nothing
is destroyed.


Craig 'Lumpy' Lemke

www.n0eq.com