Hello,

I searched this group first and didn't find an exact answer to my
situation. I have a large attic in a single story 2100 sq ft. house. I
just bought this house a few years ago and it is to be my retirement
home. Recently, I got the ham radio bug again and have most of my new
gear here ready to go and I overlooked the fact that there is foil on
the back of my attic roofing. I am disabled and cannot get in the attic
easily and usually have to get my wife or somelse go up there. So I
overlooked this.

I want to operate most VHF but I like 20 CW and 10 FM and 6 meters -
440 mhz both SSB and FM. So I've been trying to come up with an antenna
to cover that. I have the antennas pretty much decided but Bingo -- the
roofing material problem pops up and I don't have any idea how much
signal I will lose through that stuff. If it is a few DB and messes the
pattern up a little I don't care, but if it is 20 db and won't tune I
do care. I'm not a contester -- just like to have fun and have a 100
Watt FT-857D and I'll keep the power down to were I don't start triping
the GPFs

I have used a HT downstairs and never suspected a problem because it
was a little VX-2R and I mostly just listened with it but I could hear
all the repeaters and the aircraft band came in like gang busters and
SW Broadcast was loud on a little whip. I just sold the HT when I
ordered the new rig so I can't make the tests I would like up in the
attic now.

Does anyone have any experience with this kind of attic. I have heard
everything from it wont work to people that said it worked better than
in other standard plywood attics.

I thought a shield had to be at "ground" potential to effectively block
a signal (eg Faraday shield). For instance shielded audio cable remains
unshielded unless grounded at one end. Does the same hold true for this
foil barrier heat shield?

Any help will be appreciated.

Thanks,
Frank, K5OX

Well Frank, you are in a bind if the in-the-attic antenna is all you
can put up, especially for HF... The foil is an impenetrable barrier to
RF trying to launch upwards...
How about loading the gutters around the house?
How about a flag pole vertical? Or even a pair for switchable end-fire
/ broad-side...
For a bit of money one of the pneumatic poles would make a great flag
pole.. Down for 20 during the day and up for 40 at night...
How about a screwdriver tunable whip mounted somewhere on the center of
the roof (if outside antennas are verboten you can call it a lightning
rod), with the foil underneath and a few radials this should play...
Or as an angled "flag pole' off an upper window sill...
Maybe the wife would like a pulley clothes line for drying clothes -
from the second story window? If it just happens to be a quarter wave
on 40 meters the clothes should dry that much better...
(ya, ya, ya, I know you wet nosed kids don't have a clue what a pulley
clothes line is - so expand your education)
How about a wire up the chimney? To a lightning rod?
As a last resort a wire can be run around the inside of the roofing
insulation with a short screw into each sheet of foil board so it is
all bonded... Then a vertical wire from the first floor, or the
basement and load this as a vertical with a big top hat... You will
need a good set of ground radials to work it against...

gl denny / k8do

wrote:
. . .there is foil on the back of my attic roofing. . .

I want to operate most VHF but I like 20 CW and 10 FM and 6 meters -
440 mhz both SSB and FM. So I've been trying to come up with an antenna
to cover that. I have the antennas pretty much decided but Bingo -- the
roofing material problem pops up and I don't have any idea how much
signal I will lose through that stuff. If it is a few DB and messes the
pattern up a little I don't care, but if it is 20 db and won't tune I
do care. . .

Does anyone have any experience with this kind of attic. I have heard
everything from it wont work to people that said it worked better than
in other standard plywood attics.

The whole range of reports could be completely true. There are many
variables involved, including but not limited to the width of the batts,
whether and how much they overlap or how far they're spaced, how far and
how they're oriented relative to the antenna, the type of antenna, the
frequency, possibly the thickness of the aluminum, and the directions
and elevation angles of desired communication.

So any binary answer of "works" or "doesn't work" has a 50% likelihood
of being right. I generally use a coin to make this sort of decision.

I thought a shield had to be at "ground" potential to effectively block
a signal (eg Faraday shield).

Nope, not at all. To be effective, an RF shield has to be continuous,
that is completely enclose what it is you're trying to shield. Shielding
DC electrostatic fields is another matter and not applicable here. Your
foil insulation makes a lousy shield at HF. But that's not to say it
won't have some profound effects, as I elaborate below.

For instance shielded audio cable remains
unshielded unless grounded at one end. Does the same hold true for this
foil barrier heat shield?

Nope. A shielded audio cable works somewhat differently than a coax
cable carrying RF or an RF shield.

An HF antenna will be close to the foil in terms of wavelength. It will
induce a current on the surface of the antenna side of the foil. This
will flow around the edges of the foil to the outside, where it'll
become the real antenna and radiate. The field from this conductor will
(vectorially) add to whatever field escapes from the intended antenna
itself, so the net field will be a combination of the two. The only
practical way to find out what the result will be is to try it. The
proximity of the foil will also modify the impedance of the antenna,
very possibly in a major way. So classical formulas for antennas in free
space might be way off, and if so you'll probably need a tuner to match it.

What I don't know is whether the radiant barrier, which apparently is
often much thinner than a conventional foil insulation moisture barrier
and perforated to allow moisture through, might be thin and irregular
enough to be lossy. But I kind of doubt it.

Good luck!

Roy Lewallen, W7EL

Roy, as a novice for Field Day it was raining cats and dogs... I went
to the family farm out in the boonies and hung a 40 meter dipole the
length of the barn, in the rafters and out of the rain...... Didn't
occur to me that being about 8 feet under the metal roofing would be a
problem... Well, even as a really green novice I knew when an antenna
was a dog... That dipole couldn't even hear itself... And that is with
the dipole being 35 feet in the air in the rafters... My Lafayette kit
receiver (copy of an S-38, boy did those half circle dial indicators
look cool) and a rock bound HeathKit DX-35... I froze my butt off in
the milk house that night trying to make contacts... I don't remember
the exact number but it could not have been more than 25 Q's... About
4AM I gave up and went back to town...

denny / k8do



Roy Lewallen wrote:
wrote:
. . .there is foil on the back of my attic roofing. . .

Frank,

Unfortunately, the results are very much of the "it depends" nature. A
good friend in a condo with a similar situation does very well for
short hops with a dipole and remote tuner in the attic, with some
occasional DX thrown in on PSK31. With the "ground" so close, he is
mostly seeing NVIS propagation into adjacent states. However, it is
the only option due to the HOA.

He has one of those XM radios which can be used in the car or house.
The only place it would work in the house was inconveniently near a
window until he cut out a section of the insulation backing directly
above the desired location. Works fine now.


--
Alan
WA4SCA

Roy Lewallen wrote:
wrote:
. . .there is foil on the back of my attic roofing. . .
I want to operate most VHF but I like 20 CW and 10 FM and 6 meters -
440 mhz both SSB and FM. So I've been trying to come up with an antenna
to cover that. I have the antennas pretty much decided but Bingo -- the
roofing material problem pops up and I don't have any idea how much
signal I will lose through that stuff. If it is a few DB and messes the
pattern up a little I don't care, but if it is 20 db and won't tune I
do care. . .
Does anyone have any experience with this kind of attic. I have heard
everything from it wont work to people that said it worked better than
in other standard plywood attics.

The whole range of reports could be completely true. There are many
variables involved, including but not limited to the width of the batts,
whether and how much they overlap or how far they're spaced, how far and
how they're oriented relative to the antenna, the type of antenna, the
frequency, possibly the thickness of the aluminum, and the directions
and elevation angles of desired communication.

Hi Roy,

This may be known only to people who live where the sun actually appears
in the sky on regular occasions. What Frank is talking about is not
ordinary foil-backed insulation batts. It is now very common in the
South for the plywood sheeting used in roof structures to be completely
covered with a bonded aluminum foil which serves as a radiant barrier.
The only gaps are the small cracks between the plywood sheets. It is not
the same as a completely solid sheet of aluminum, but the continuous
aluminum pieces are much larger, and the gaps are much smaller than
those that would be found in a typical installation of foil-backed
insulation.

Your answer of "it depends" is of course completely correct.

73,
Gene
W4SZ

You won't know until you try. A 20m dipole should be easy enough to
get into any attic, and give it a shot. You might be pleasantly
surprised, and that odds that you'll be terribly disappointed are
pretty small.

Irv VE6BP


--
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Visit my HomePage at http://members.shaw.ca/finkirv/index.html
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--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

"Irv Finkleman" wrote in message
...
You won't know until you try. A 20m dipole should be easy enough to
get into any attic, and give it a shot. You might be pleasantly
surprised, and that odds that you'll be terribly disappointed are
pretty small.

Irv VE6BP

I've used lots of Dipoles in weird places and have gotten contacts. In low
sunspot its not much
but your still communicating. I used an Inverted L next to a apt building
from my 2nd floor apartment
and worked the world (High Sunspot time) . Remember, beams were not
really in big use until the 40s.
Even then it took a while for it to catch on.


Scotty W7PSK.

In article ,
Gene Fuller wrote:

Roy Lewallen wrote:
fgra

maybee you can somehow use the foil to your adv, assuming that just
hooking up your dipole dosn't work right


maybe a upsidedown vert using the foil as a gp you could attach the
foils together w/a jumper wire

or perhaps even tune the foil up as the antenna


prob not an ideal design but you knever no

In almost fifty years of hamming I never had an antenna
that was anywhere near ideal. For many years I couldn't measure let alone
spell SWR! I tied the wire onto the output of the pi-network and
never considered antenna tuners. I thought the cold water pipe was great and all
I needed. My antennas were too high, too low, or tilted the
wrong way. Most were bent around corners, and resembled
the fractal. Propagation let me think that if I got the signal into
the air it would bounce around till I made a contact. If I heard
someone I could usually work them. The RF burns were thrilling, and
told me that I had output! I fired my arrows into
the air and never ceased having fun. Ignorance was bliss. If
I'd known much about antenna theory I'd still be working on the plans
instead of on the air!

Irv VE6BP


"R. Scott" wrote:

"Irv Finkleman" wrote in message
...
You won't know until you try. A 20m dipole should be easy enough to
get into any attic, and give it a shot. You might be pleasantly
surprised, and that odds that you'll be terribly disappointed are
pretty small.

Irv VE6BP

I've used lots of Dipoles in weird places and have gotten contacts. In low
sunspot its not much
but your still communicating. I used an Inverted L next to a apt building
from my 2nd floor apartment
and worked the world (High Sunspot time) . Remember, beams were not
really in big use until the 40s.
Even then it took a while for it to catch on.

Scotty W7PSK.

--
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/index.html
Visit my Baby Sofia website at http://members.shaw.ca/finkirv4/index.htm
Visit my OLDTIMERS website at http://members.shaw.ca/finkirv5/index.htm
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada