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rickman · March 25th 16, 11:50 PM posted to rec.radio.amateur.antenna

On 3/25/2016 5:06 PM, Pat wrote:
On Fri, 25 Mar 2016 14:54:16 -0400, rickman wrote:

On 3/25/2016 2:10 PM, Pat wrote:
On Fri, 25 Mar 2016 10:58:35 -0400, rickman wrote:

On 3/25/2016 8:50 AM, Roger Hayter wrote:
Pat wrote:

On Fri, 25 Mar 2016 12:04:11 +0000, (Roger Hayter)
wrote:

Pat wrote:

My antenna theory knowledge is a little weak so I thought you guys
might be able to help.

Background:
I have a shed about 50 feet away from my house that contains water
pumps and similar equipment that I monitor. The shed has no windows
but was built using normal stud-wall construction. I built a small
device that receives information from sensors and then reports back to
my PC via my home network. I have no way to run wires to the shed
because there is a driveway in between, so I decided to use wi-fi. The
shed had a good strong wi-fi signal inside it and everything worked
well for the last 5 years. Recently, vinyl siding was added to the
shed. The installers used foil coated styrofoam insulation under the
siding. The shed has changed from being fairly transparent to RF to
being a somewhat leaky faraday shield. The wifi module still works,
but just barely. There are lots of missed messages and any
interference from devices like the microwave oven in the house shut
down communications.

Question:
I want to create an RF "window" in the shed wall. How big does it
need to be to let 2400 MHz signals pass through it? A full
wavelength? Half wavelength? Should it be rectangular or would a
vertical slot work? Opening the shed door (a full size metal door)
temporarily restores a strong signal, but I was hoping a much smaller
opening would work equally well. For aesthetic reasons, I can't
experiment by cutting various size holes. What's the smallest hole I
can cut in the foil coated insulation and be reasonably assured it
will work?

4mm, to take the coax to an outside wifi aerial. If you can't find a
wifi unit with an aerial socket, change this to usb cable to an outside
wifi dongle. but you may then need a 12mm hole for the USB plug.

What you have suggested is my "Plan B". The wifi module I am using
does not have removable antennas and the sensor box does not have USB
capabilities. Thanks for responding. ...Pat

I would look into how to couple an external aerial to the built-in
aerial of an existing wifif module. ISTR people doing this.

Altenative, how about putting a window either in the wall towards the
wifi source, or. depending on the roofing material, in the roof which
can sometimes be done with acrylic or polycarbonater replacement roofing
elements?

There's a point. If the metal was added to the walls only, you might be
able to rise above that by placing the antenna at the highest point of
the roof. I assume that is accessible in a shed.
Not this shed. Whoever built it finished the inside with drywall on
the walls and ceiling - no access to the attic. (By the way, I expect
the signal I am getting now is via the ceiling/roof.)

I wanted to modify the lighting on my porch. The ceiling is covered
with wood. So I cut a panel and framed it with some nice wood to make
an access hatch. You can do the same thing with the drywall.

I ended up using a plastic cover plate I found at Home Depot. It is
essential what you are recommending, but instead of making it from
wood, it comes ready made. It only cost $14 USD. It has a frame that
spans to studs and a 14" x 14" removalble door insert. Not as nice as
what you propose, but for the shed, it is one of the nicest looking
things in there :-)

Mine was basically free. The wood was reused as the removable panel and
the trim wood was scrap. I think I nail the trim to the door and used a
couple of screws to hold it to the ceiling. Still $14 is not much more
than free and saves some work.

--

Rick