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Pat[_7_] · March 25th 16, 08:58 PM posted to rec.radio.amateur.antenna

On Fri, 25 Mar 2016 18:32:37 -0000, wrote:

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.)

Pat

Drywall is very easy to cut and patch up.

Cut an access hole in the ceiling and put the RF stuff on top of the drywall.

Put a trap door over the access hole if you want to keep it all neat.

The problem with that is the shed has a gable roof. The new siding
and foil backed insulation goes all the way to the peak on the ends.
Unfortunately, the wifi signal comes from one of those ends.

Pat