"Spin" wrote in message
...
Is it possible to construct a random length receiving
antenna by capactive loading it thru a window? Both sides
of the window with a glued sheet of copper & random length
of wire soldered to the outside copper with a strain
relief. Inside copper soldered to wire which is connected
to a matching unit. Or two sheets of copper on both sides
of a window so that i can use coax or ladder line? What
about the feasability of inductive loading in the same
manner?
A random wire receiving antenna is quite non-critical.
It possible to get adequate coupling by pasting aluminum
foil on both sides of a glass window. If you want to
calulate the capacitance the approximate formula is quite
simple:

C = 0.224 KA/d (n-1)

Where

C is capacitance in uuf
K is dielectric constant of the material. For window glass
this is about 8.0
A is the area of _one_ plate in inches squared
d is the separation between the plates un inches.
n is the number of plates.

Typical window glass is about 1/8th inch thick.

For a 10 inch square on both sides (it can be round if
you prefer) the capacitance is about 22.5 uuf, for a 15"
square its about .003 uf, the capacitance increases with the
area so it goes up pretty fast as the linear dimensions are
increased.

A foot square should give you enough coupling for an
all-wave antenna. Remember than singnal strength at
broadcast frequencies is likly to be high so a smaller cap
may be an advantage.
You definitely do NOT need copper plate, plain aluminum
wrap will do nicely. It can be pasted on the glass with
spray adhesive but keep in mind that you probably will want
to remove it some day so peel off adhesive might be a good
idea. This can be obtained in art supply or photographic
supply places. If you are in an area where the outside is
subjected to bad weather, for instance, very cold
temperatures or a lot of moisture, you might need to use a
more permanent adhesive.
You can fasten the wires to the aluminum with an
aligator clip on either side. Leave an un-cemented strip for
this.
Of course, the wire should have some sort of strain
relief since it will just tear off the aluminum foil.
For transmitting one can use a similar trick but its
not so simple.


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Richard Knoppow
Los Angeles
WB6KBL