Andy writes:

I would like to hear some discussion/advice on the feasibility of
putting
an antenna for, say, 30m in the attic versus on top of the roof...

Here is the situation :
The roof peak of my house is about 50 feet and is straight. Given
the
need for a dipole which is 44 feet wide, it can be mounted in either of
two
places:

1) Just above the roof peak, straight along it, about 1 foot above.

2) Just below the roof peak,inside the attic, about 1 foot below .

Let's assume there are no other options...


So it sort of boils down to whether the wood and asphalt barrier ,
free
of metal except for an occasional nail, actually attenuates the signal
enough
to bother about, or affects the antenna impedance enough to bother
about.....

Having made dozens of ham antennae over the last 40 years in
configurations
that probably violate the laws of physics and having had them work, I,
personally,
haven't found that such a difference in the antenna placement makes a
hill
of beans worth of REAL difference (no pun). But a lot of guys here
have been
doing this for 40 years also, and I'd really like to see what anyone
has to say
about it.....

I generally use one rule of thumb on antennae:

" If when I connect the antenna to the receiver, the background
noise
of the receiver increases, the antenna is doing a good job".....

Yeah, I know, but it needs some thinking about because if the cosmic
noise
level picked up by the antenna is higher than the receiver noise level,
then
it has to be working........assuming it is cut to the proper frequency
for the
band used.....

So, what about it ? Anybody want to put in their two cents worth ?


Andy W4OAH

ORIGINAL MESSAGE:

On 10 Dec 2006 07:42:23 -0800, "AndyS" wrote:

Having made dozens of ham antennae over the last 40 years in
configurations that probably violate the laws of physics and having had them work, I,
personally, haven't found that such a difference in the antenna placement makes a
hill of beans worth of REAL difference (no pun). But a lot of guys here
have been doing this for 40 years also, and I'd really like to see what anyone
has to say about it.....


------------ REPLY FOLLOWS ------------

If the antennas you're talking about really did work, you did not
violate any laws of physics, I can assure you. :-)

I operated with in-attic antennas for years and they do work
surprisingly well. I earned DXCC with 100 watts and an attic dipole in
a matter of a few months.

Go for it.

Bill, W6WRT

I would like to hear some discussion/advice on the feasibility of
putting
an antenna for, say, 30m in the attic versus on top of the roof...

Here is the situation :
The roof peak of my house is about 50 feet and is straight. Given
the
need for a dipole which is 44 feet wide, it can be mounted in either of
two
places:
================================================
Andy , You didn't provide the shape of your roof space eg width at loft
bottom and whether there is any metal around (apart from nails/screws
etc). For an HF roof space antenna I would recommend a wire loop as
much as possible away from any metal and with total loop length
exceeding the the length of the largest wavelenght you wish to operate
on. So in your case a loop of 10m or say 35 ft would be adequate

A square would be the optimum ,but a 'wide rectangular' is acceptable.
Feed the loop with any balanced feeder ,twinlead electrical cable'(75
Ohms ?) or 300 -450 Ohms ribbon or 2 wires with insulator spacers.

It would be best to feed the loop somewhere near the middle of a side

You obviously need a balanced tuner/matching unit ,but might get away
with a simple current balun

Good luck

Frank KN6WH / GM0CSZ

Highland Ham wrote:
================================================
Andy , You didn't provide the shape of your roof space eg width at loft
bottom and whether there is any metal around (apart from nails/screws
etc). For an HF roof space antenna I would recommend a wire loop as
much as possible away from any metal and with total loop length
exceeding the the length of the largest wavelenght you wish to operate
on. So in your case a loop of 10m or say 35 ft would be adequate

A square would be the optimum ,but a 'wide rectangular' is acceptable.
Feed the loop with any balanced feeder ,twinlead electrical cable'(75
Ohms ?) or 300 -450 Ohms ribbon or 2 wires with insulator spacers.

It would be best to feed the loop somewhere near the middle of a side

You obviously need a balanced tuner/matching unit ,but might get away
with a simple current balun

Good luck

Frank KN6WH / GM0CSZ


Andy replies:

Thanks for taking the time to give me your advice. However, do
you have an answer or opinion about the question that I asked ?

Andy W4OAH

"AndyS" wrote in message
ups.com...

1) Just above the roof peak, straight along it, about 1 foot above.

Is the ridge vent metal? Usually it is covered with shingles, but sometimes
it is aluminum, sometimes plastic. I trust any foil backed insulation is in
the floor of the attic rather than the roof.

All other things being equal, I would expect the antenna to be noticeably
better above the roof, because there will be some attenuation indoors, and
greater proximity to noise makers, and things that can get overloaded by
your transmitter.. But I doubt it would be a huge difference, although on
wet days it may well be sigificant. If the vent is metal, then the attic
antenna, because you can get it farther from the vent, may well be better.

But "better" is a relative term. I suspect in 4-land you don't get the snow
and ice we get up here on the tundra, but I imagine you have pretty decent
storms come by once in a while. It may well be that the slight attentatuon
is a small price to pay for not having to re-string the antenna every time
hurricane season rolls around.

...

xpyttl wrote:

Is the ridge vent metal? Usually it is covered with shingles, but sometimes
it is aluminum, sometimes plastic. I trust any foil backed insulation is in
the floor of the attic rather than the roof.

**** Correct. All the metal is well removed. Just a wood
sheathing/asphalt
shingle roof..


All other things being equal, I would expect the antenna to be noticeably
better above the roof, because there will be some attenuation indoors, and
greater proximity to noise makers, and things that can get overloaded by
your transmitter.. But I doubt it would be a huge difference, although on
wet days it may well be sigificant. If the vent is metal, then the attic
antenna, because you can get it farther from the vent, may well be better.

**** I didn't think of the "wet days" situation..... I haven't seen
much difference
in antenna performance due to rain or weather tho... However, it
doesn't
snow here much at all.


But "better" is a relative term. I suspect in 4-land you don't get the snow
and ice we get up here on the tundra, but I imagine you have pretty decent
storms come by once in a while. It may well be that the slight attentatuon
is a small price to pay for not having to re-string the antenna every time
hurricane season rolls around.

**** No hurricanes in Eureka, Texas... Just tornadoes... And the
antenna
will usually land somewhere around where the house comes down at .....
:)))))

*** The main reason for the question is my wife's opinion of acceptable
adornment for the exterior of our new house...... She doesn't share
my fascination with "electronical stuff" as an art form...

:) Andy W4OAH in Eureka, Texas

"AndyS" wrote in message
ps.com...

*** The main reason for the question is my wife's opinion of acceptable
adornment for the exterior of our new house...... She doesn't share
my fascination with "electronical stuff" as an art form...

Ahhh, well. That changes things. A wire antenna is practically invisible,
but you wouldn't want it in the attic where it could attract lightning
inside the house.

...

xpyttl wrote:
Ahhh, well. That changes things. A wire antenna is practically invisible,
but you wouldn't want it in the attic where it could attract lightning
inside the house.

..
Andy comments:
Well, the difference between being "practically invisible" and
being
pre-emminent in grotesqueness to my wife is "practically negligible"
(grin).

I'm not certain that an antenna "attracts" lightning. It probably
makes
little difference between hitting an outside antenna, running in the
feedline, and burning down the house VERSUS going thru a layer
of asphalt shingles and doing the same thing...... but I can see where
you're coming from.....

However, in Eureka we don't usually have problems with lightning
because the tornado usually blows the antenna away before the
lightning strikes......

Andy W4OAH in Eureka, Texas

AndyS wrote:
*** The main reason for the question is my wife's opinion of acceptable
adornment for the exterior of our new house...... She doesn't share
my fascination with "electronical stuff" as an art form...

Well that settles it in my mind, do it inside the roof as high as u can get it.
(use rope and pulleys so u can later play with it, when the urge hits)
It should work almost as well as of it were outside and 3 foot higher.
Easy to get the feel line to come away at a 90 degree angle.
(not necessary, but if it does great)

and last but not least
It will save up your exterior adornments play with the xyl for a later project.

Sam Morgan wrote:
It will save up your exterior adornments play with the xyl for a later project.

Andy comments:
Yeah, you would not BELIEVE the size of the television antenna we
need
here to get good reception (grin)........fortunately Moseley makes a
good
one.... :)))))

Andy W4OAH