"Haines Brown" wrote in message
...
"Mike Kaliski" writes:

"Haines Brown" wrote in message
...
Automotive couplers for two metres manage with a 2 inch by 2 inch
plate either side of the glass. It could be worth trying 6 inch by 6
inch plates on the domestic window and see what signal level gets
out. Reception shouldn't be a problem if you can get 50% or more of
your transmission power out through the glass.

The suggestions for a panel to insert into a partially opened window and
to close the window on twin lead seem out. It's a steel casement type
window that must be fully shut, and even if twin-lead were to get around
the edge, it would be sandwiched in steel. I don't own the wall, so even
if a hole could be put in it (which it can't), I don't own it.

On the positive side, this is a single pain of ordinary class, and I
could make a capacitative coupler over 12" square and still get too near
the steel frame. It's a curtained window, and so appearance is not
important.

A question. Is this coupling purely capacitative at this frequency (the
more surface area the better), or is it somewhat tuned (try different
sizes to see what signal level gets out).

An obvious question, how can the coax be connected to the sheets of
metal? That is, what happens to the braid? Or could there be two sheets
next to each other on both sides of the glass, say one foot square each,
with one for the coax center conductor and one for its braid?

The only advantage that a commercial coupler might have is that the
visual asthetics might be a bit better than a home brewed effort.

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.

--

Haines Brown, KB1GRM

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.

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.

Mike G0ULI

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 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

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