how to block 108 MHz radio waves

I live near a small airport, and I am sensitive to SOMETHING there, but i'm
not sure what. What I do know is all of the devices emitting radio waves
coming off of this airfield are just above 108 MHZ. So I'm trying to create
a safe place for me to sleep until I sell this house and move. I have an FM
radio, and since the frequency coming out of the airport is just above the
FM frequency range, I thought as a good test if I could create an
environemnt, literally even like a metal box around my bed, where I
couldn't get radio reception then I would also be blocking the stuff coming
from the airport. But how do I do this? I've done experiements of putting
this radio in a metal pot, etc. but it still works. I though metal was
supposed to block these radio waves. Could someone advise me what to do
here, and why the radio still works in a sealed metal pot? Thanks.

--
Paul Coffman


[Non-text portions of this message have been removed]

The metal pot may act as a resonator. I think my copper paint walls are
doing just that.
Also there are frequencies from ground radar ( so I've been told) and
also very high frequency stuff 10G+.
I am no expert here and would like to learn more.
The upshot is good luck living near an airfield.
I too live about 10 miles from one.
I thought that distance would be enough.
Now there are weather radars and god knows what else in addition to the
gas, electric and water meters just installed in the neighborhood.

Look forward to the responses from the experts.
Andrew


On Oct 21, 2007, at 8:47 PM, Paul Coffman wrote:

If you had good conductivity between the lid and the pot, not just at one
point but all the way around the seam, then I'd expect pretty dramatic
attenuation. However, with FM, the volume may not get lower when the
signal is cut down (although it might be a little noisier, and stereo will
be
gone).

I think if the pot is the thick (cast) aluminum kind and the lid also (but
I've never
seen that) you should have very good attenuation. On the other hand,
the radio is close to the walls and floor of the pot, so there could be near
field
issues.

If we assume these signals are strong and you are very sensitive then you
may need serious attenuation. I'd expect a professional screen room would
do
it. There exist portable screen tents in the $2k-$11k range, but by default
they
don't have much ventilation, at least for the cheaper ones. It's hard to
know in
advance if a single layer one will do it or if you need a double wall.

There's also bed canopies; I think the Aaronia ones have the best
attenuation.
With a ground pad I'd expect good results (but haven't tried one).

If you want to make your own thing:
The frequency you're talking about is pretty low, so holes up to 1/8
wavelength (.4m) are OK, but you need to make sure the seams are
conductively sealed.
I guess if it were me I'd look into aluminum sheet metal or maybe better
thick aluminum foil,
but be prepared that multiple layers may be needed, and allow lots of
overlap. I've been given conflicting advice as to whether it's OK
to have metal staples or fasteners penetrate the shielding. Certainly
professional jobs do not have
them. But, you certainly can get dramatic (but maybe not sufficiently
dramatic) attenuation with
stapled foil.

I think I'd cover the whole wall closest to the airport. Then build a
smaller wood frame and
cover with fly screen; overlap all the edges and make sure to have fasteners
every .2 m or better.
In fact you want electrical contact all along the seems, not just where the
fasteners are.
At this wavelength (unlike with microwaves) you cannot neglect the ceiling
and floor. And again
take care with the seems. A professional door would have fingerstock all
around to get good
contact. Put the door away from the airport side. There is conductive
velcro if you use fabric.

Grounding is also probably a good idea at this frequency; just one ground
wire to a long stake.
Keep the wire short and straight (and ideally wide).

I guess I would just do the airport wall and floor first, ground it, and
hope that I felt better down in the
seam between them. If so the shielding is thick enough to continue.

This is all guesswork for me, I've only shielded microwaves successfully.
I'm told Donald White's
volume 3 on electromagnetic shielding is the book to have. I have another
one and I don't like it.

Good luck, let us know how it goes,
Bill


On 10/21/07, Paul Coffman <[hidden email]> wrote:

[Non-text portions of this message have been removed]

I've heard of someone buying one of those outdoor metal toolsheds and
actually constructing it within a room in their house.

Seems awfully extreme to me and no guarantee it would help.


John Lankes


--- In [hidden email], "Paul Coffman" <pkcoff@...> wrote:
>
> I live near a small airport, and I am sensitive to SOMETHING there,
but i'm
> not sure what. What I do know is all of the devices emitting radio
waves
> coming off of this airfield are just above 108 MHZ. So I'm trying
to create
> a safe place for me to sleep until I sell this house and move. I
have an FM
> radio, and since the frequency coming out of the airport is just
above the
> FM frequency range, I thought as a good test if I could create an
> environemnt, literally even like a metal box around my bed, where I
> couldn't get radio reception then I would also be blocking the
stuff coming
> from the airport. But how do I do this? I've done experiements of
putting
> this radio in a metal pot, etc. but it still works. I though
metal was
> supposed to block these radio waves. Could someone advise me what
to do
> here, and why the radio still works in a sealed metal pot? Thanks.

> I've heard of someone buying one of those outdoor metal toolsheds and
> actually constructing it within a room in their house.
>
> Seems awfully extreme to me and no guarantee it would help.

Yes, it seems very extreme, and you also run the risk of it
making things worse, I would think (since you are also shutting
out beneficial effects from the sunlight coming in through the
windows)

Marc

 
In a message dated 10/22/2007 6:34:11 PM GMT Daylight Time,  
[hidden email] writes:

Seems awfully extreme to me and no guarantee it would help.

Yes, it seems very extreme, and you also run the risk of it
making things worse, I would think (since you are also shutting
out beneficial effects from the sunlight coming in through the
windows)




Many years ago I bought a metal bunkbed for my son, long before I had any
grasp of the complexity of the ES situation, needless to say having lovingly  
built it I stood back and realised that all was not well I could sense the  
change in the room which made me feel very uncomfortable, I took it down lost £50
in refund, got my son a wooden bed the rest is history ! Larg metal  
structures in houses not good idea !
 
p uk



   


[Non-text portions of this message have been removed]

I've been told that solid wood shielded with
aluminum is affective. Once I built a wood cabinet
which enclosed my LCD monitor and it did provide
some relief. A solid aluminum enclosure, on the
other hand, was horrible.

Eli