[This post is sent again in plain text (cannot avoid that). I've
used a monospaced font type, "courier new", font size, "smaller"
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ay need to adjust your viewing font (ToolsOptionsReadFonts)
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I've no real experience of putting up antennas on the chimney
of a house.

Obviously, I must not overload the chimney breast.

I'm thinking about putting up the following:


_______ Discone
/ | \
__ / || \
A |
__ ___|x___ 5 ele.2m yagi
|
B | |
__ |x| 5 ele. marine yagi
| |
C |
| |
__ |x| 5 ele. FM yagi.
| |
D |
|
__ |
/ \ Rotator
/___\
|
| ______
| | | Chimney
| | |
| | |

I'm wondering about the spacings, A, B, C, and D.

A, spacing between bottom of the discone and the boom of 2 m yagi.

B, spacing between boom of 2m yagi and boom of marine band yagi.

C, spacing between boom of marine band yagi and boom of FM yagi.

D, spacing between boom of FM yago and top of rotator.

As for the mast, I'm thinking what about 1.5" steel tube.

As for rotator. No idea what model I'd need.

Any thoughts? Am I trying to be too ambitious? I could
leave out the marine yagi if I had to.

Thanks.

Rich.

"Richard Clark" wrote in message
...
On Tue, 17 Feb 2004 17:47:39 -0000, "Richard"
wrote:

I'm wondering about the spacings, A, B, C, and D.

Hi Richard,

You should be thinking more of the tensile failure of the brick mortar
leveraged by the moment of the load above. Chimneys are very strong
to compressive loads, and as brittle as candy to torsion.

Hi,

I confirmed too that you will experiment problems with the maconnery.
I attached the end of a G5RV to my chimney, fine, no problem for years, but
the vertical damaged the bricks and the cement udner high wind.
A small roof pylon (2-3m high) is by far preferable and more secure.

Thierry
ON4SKY
http://www.astrosurf.com/lombry/menu-qsl.htm



The upshot of this is that on a windy night you may find the chimney
in your bed.

73's
Richard Clark, KB7QHC

I wouldn't do it.
"bunnydawg" wrote in message
.. .
I'm wondering if your chimney will handle the weight ?
Robert

"Richard" wrote in message
...
I've no real experience of putting up antennas on the chimney of a
house.

Obviously, I must not overload the chimney breast.

I'm thinking about putting up the following:


______ Discone
/ | \
__ / || \
A |
__ ___|x___ 5 ele.2m yagi
|
B | |
__ |x| 5 ele. marine yagi
| |
C |
| |
__ |x| 5 ele. FM yagi.
| |
D |
|
__ |
/ \ Rotator
/__\
|
| ______
| | | Chimney
| | |
| |

I'm wondering about the spacings, A, B, C, and D.

A, spacing between bottom of the discone and the boom of 2 m yagi.

B, spacing between boom of 2m yagi and boom of marine band yagi.

C, spacing between boom of marine band yagi and boom of FM yagi.

D, spacing between boom of FM yago and top of rotator.

As for the mast, I'm thinking what about 1.5" steel tube.

As for rotator. No idea what model I'd need.

Any thoughts? Am I trying to be too ambitious? I could leave out the
marine yagi if I had to.

Thanks.

Rich.

On Tue, 17 Feb 2004 22:41:16 -0000, "Richard"
wrote:
[This post is sent again in plain text (cannot avoid that). I've
used a monospaced font type, "courier new", font size, "smaller"
to view the page on my PC. To correctly view the ASCII art, you
ay need to adjust your viewing font (ToolsOptionsReadFonts)
to: Proportional Font: "Courier new" Font size: "smaller".]


Hi Richard,

It may look good to you, but for many it remains sloppy.

The convention of ASCII-Doodles is to employ fixed pitch fonts. This
is available to everyone.

A, spacing between bottom of the discone and the boom of 2 m yagi.
0.5M to 1M
B, spacing between boom of 2m yagi and boom of marine band yagi.
0.5M to 1M
C, spacing between boom of marine band yagi and boom of FM yagi.
0.5M to 1M
D, spacing between boom of FM yago and top of rotator.
0.5M

Proximity is more likely to disturb the depth of nulls than to rob
gain. Proximity will also pull resonant frequency. Recommendations
will run the gamut where a purist would demand 1 to 5 wavelengths.
Practice often accepts much less when offset by sweat-equity (more
tuning and trimming on your part).

Don't forget guy wires to preserve the mortar (its not the brick that
breaks); and don't forget to break up the guys to prevent their
resonance effects (or use non-conductive guys).

73's
Richard Clark, KB7QHC

Hi,

One thing I have not seen in previous replies,

If you use a band clamp to attach the mast to the chimney,
water can get behind the metal band and when it freezes, cause
damage to the brick.

In warm weather, the bricks expand and the metal bands
damage the bricks.

I'm not an engineer but another post recommended to use guy
wires so to reduce windload off the chimney.

I don't believe this will reduce windload at all, the guys will
be attached to the mast only and not the actual antenna so
no reduction in windload.

Best to avoid using the chimney and attach the mast to the house
at the eave using long bolts and nuts attached to some pressure treated
(and painted) 2x4's on outside and inside the attic. stronger and
you don't have to worry about the coax getting too hot from the heat
of the chimney exhaust.

mick

A chimney is one of the worst places you can locate an antenna. They
appear to be handy, but even on an old chimney there are corrosive
gases that will really do a job on Aluminum. Gas fired furnaces are
bad, wood is worse,a nd coal is terrible.

If the chimney appears to be solid enough to hold a small antenna,
(they rarely are strong enough to hold much more than a VHF, or TV
antenna) then give all the aluminum about 4 or 5 coats of clear
Krylon. Give the coax connector and attach points several coats of
liquid electrical tape.

Even then it most likely will have to be done every year or two at
best.

Steel mast fittings will rust beyond repair within just a few months.
They'll hold, but usually have to be cut off, or will twist off when
an attempt to remove the nuts is made.

If at all possible, put the antennas some where other than on a
chimney.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

"Richard Clark" wrote in message
...
On Tue, 17 Feb 2004 22:41:16 -0000, "Richard"
wrote:
[This post is sent again in plain text (cannot avoid that). I've
used a monospaced font type, "courier new", font size, "smaller"
to view the page on my PC. To correctly view the ASCII art, you
ay need to adjust your viewing font (ToolsOptionsReadFonts)
to: Proportional Font: "Courier new" Font size: "smaller".]


Hi Richard,

It may look good to you, but for many it remains sloppy.

The convention of ASCII-Doodles is to employ fixed pitch fonts. This
is available to everyone.

Hi.

I have used fixed pitch on the second post. Courier new is fixed
pitch/monospaced.

I beleive the viewer though has to change the veiwing font to courier new.

When a body in the form of a rod or a tube, albeit a short rod, is placed
under torsion, ie., it is subjected to a TWISTING MOMENT, then SHEAR
stresses are set up in it.


The shear stresses are in the plane of the cross-section - adjacent
cross-sections tending to slide over each other.


When the body experiences a sideways thrust, as from wind, then a BENDING
MOMENT is set up in it. One side of the body is under vertical TENSION and
the other side is under vertical COMPRESSION.


Brickwork and concrete are much the weakest when under tension. Not so weak
when under shear. Much the strongest when under compression.


The weight of brickwork exerts a uniform compressive stress over the
cross-section. Initially there is no tensile stress. But the bending moment
due to wind on ONE side of the structure eventually overcomes the
compression. On THAT side the stress becomes tensile and the brickwork parts
company with itself, ie., the structure initially fails under tension.


It is only AFTER failure has occurred due to tension that shearing takes
place and bricks begin to slide sideways, one over the other.


The art in the design of brick and concrete structures, eg., as for
chimneys, bridges and gravity damns, is NOT to allow any TENSILE stresses to
be set up. Hence the frequent use of steel reinforcement.


Memo: In view of the variability in such materials apply large factors of
safety.
----
Reg, G4FGQ

"R. Torsten Clay" wrote in message
...
This was with a Radio Shack chimney mount. Just the chimney mount by
itself was too flimsy. I found that it was necessary to add a set of
guys, attached just below the rotator and running to the roof
corners. The guys made the whole thing much more secure and took some
of the windload off of the chimney.

Torsten
N4OGW

What I did was to use a 10 foot Al pipe, and extend it all the way down to
the roof. This was on the inside downslope side of the chimney. I fastened
the pipe to the roof with a RS roof mount. This gave me a longer moment
arm, and took the vertical weight off the chimney. I have a rotor and 18 el
M2 432 antenna on it, about a foot above the rotor. Smaller than a large TV
antenna.

I would not do remotely what has been suggested here.

Tam/WB2TT

"Richard" wrote in message
...
I've no real experience of putting up antennas on the chimney of a house.

Obviously, I must not overload the chimney breast.

I'm thinking about putting up the following:


______ Discone
/ | \
__ / || \
A |
__ ___|x___ 5 ele.2m yagi
|
B | |
__ |x| 5 ele. marine yagi
| |
C |
| |
__ |x| 5 ele. FM yagi.
| |
D |
|
__ |
/ \ Rotator
/__\
|
| ______
| | | Chimney
| | |
| |


This is too ambitious, I realise that now. I think one 4 or 5 element FM or
2m yagi is about what would be acceptable. And the antenna not far above the
rotator.