Hi,

A question about the installtion of a short beam on a roof/chimney.

My house is built on top of Meuse valley, 250m high, surrounded with open
field (and much wind, hi).

The roof top is at about 6m high. There is a small chimney 2m high. This
part of the house contain only the garage and in front (garden side), the
small boiler.
Here is the picture,
http://www.astrosurf.com/lombry/Radi...fil15m-eo3.jpg

I want to work mainly on bands of 20, 17 and 15m (and much less on 12 and
10, say 10% of time). So the antenna 'd be placed at 10m high and i can
reach this height : I could place a small mast 3m high on the chimney
attached with simple aluminium straps and screws, so the antenna will be at
about 10m high. I hope it will be away from any interference with the boiler
ignition system.

Question:
Is it important to place the beam much higher than the chimney (say at worst
10m higher that any building) or the main problem is the height over the
ground of the house (I suspect the second) ?

At last, any experience with a TGM MQ 36SR at various heights is welcome (I
read the eham reviews but there is not much accurate opinion in this regard,
excepting that everybody does not share its good performances...)

PS. My alternative should be to place the antenna 5 m high over ground at
the end of the garden (60m away), simply attached to the supporting wood
wall of a small cottage ... :-(

73
Thierry
ON4SKY, LX3SKY
http://www.astrosurf.com/lombry

Thierry,
With a few precautions, I'd place the antenna on the chimney. The
primary precaution is to make sure the chimney is constructed so as
to be able to support the antenna and mast! Chimneys are not usually
built to withstand very much stress from the sides, the antenna and mast
will place higher than usual stress on the chimney because of they're
wind resistance.
The effective height above ground will be slightly lower than the
antenna's actual height because of the proximity to the structure. No
idea what that effective height might be, and probably not a huge amount
of difference from the actual height above ground. In general, the more
height, the better the performance. A meter or two won't make ~that~
much difference either way, though.
I've no experience with your particular antenna so am no help there.
Good luck...
'Doc

"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm wrote
in message ...
Hi,

A question about the installtion of a short beam on a roof/chimney.

My house is built on top of Meuse valley, 250m high, surrounded with open
field (and much wind, hi).

The roof top is at about 6m high. There is a small chimney 2m high. This
part of the house contain only the garage and in front (garden side), the
small boiler.
Here is the picture,
http://www.astrosurf.com/lombry/Radi...fil15m-eo3.jpg

I want to work mainly on bands of 20, 17 and 15m (and much less on 12 and
10, say 10% of time). So the antenna 'd be placed at 10m high and i can
reach this height : I could place a small mast 3m high on the chimney
attached with simple aluminium straps and screws, so the antenna will be
at
about 10m high. I hope it will be away from any interference with the
boiler
ignition system.

Question:
Is it important to place the beam much higher than the chimney (say at
worst
10m higher that any building) or the main problem is the height over the
ground of the house (I suspect the second) ?

At last, any experience with a TGM MQ 36SR at various heights is welcome
(I
read the eham reviews but there is not much accurate opinion in this
regard,
excepting that everybody does not share its good performances...)

PS. My alternative should be to place the antenna 5 m high over ground at
the end of the garden (60m away), simply attached to the supporting wood
wall of a small cottage ... :-(

73
Thierry
ON4SKY, LX3SKY
http://www.astrosurf.com/lombry


Thierry,
I would go for the chimney. I presently have a 19 element 432 antenna and an
HD73 rotor on the chimney with a 10 foot Al. mast. Just make sure the
chimney is strong enough. I put the mast on one of the inside corners of the
chimney, and the end of the mast is actually supported on the roof. This
takes the dead weight off the chimney mounts, and makes for a longer moment
arm. Also, put it on the more upwind side.

Tam/WB2TT

"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm wrote
Hi,

A question about the installtion of a short beam on a roof/chimney.

My house is built on top of Meuse valley, 250m high, surrounded with open
field (and much wind, hi).

The roof top is at about 6m high. There is a small chimney 2m high. This
part of the house contain only the garage and in front (garden side), the
small boiler.
Here is the picture,
http://www.astrosurf.com/lombry/Radi...fil15m-eo3.jpg

I want to work mainly on bands of 20, 17 and 15m (and much less on 12 and
10, say 10% of time). So the antenna 'd be placed at 10m high and i can
reach this height : I could place a small mast 3m high on the chimney
attached with simple aluminium straps and screws, so the antenna will be
at
about 10m high. I hope it will be away from any interference with the
boiler
ignition system.

Question:
Is it important to place the beam much higher than the chimney (say at
worst
10m higher that any building) or the main problem is the height over the
ground of the house (I suspect the second) ?

At last, any experience with a TGM MQ 36SR at various heights is welcome
(I
read the eham reviews but there is not much accurate opinion in this
regard,
excepting that everybody does not share its good performances...)

PS. My alternative should be to place the antenna 5 m high over ground at
the end of the garden (60m away), simply attached to the supporting wood
wall of a small cottage ... :-(

73
Thierry
ON4SKY, LX3SKY
http://www.astrosurf.com/lombry


Thierry (http://astrosurf.com/lombry/post.htm):

in your proposed chimney-mounted antenna.

Be advised that carbon build-up from furnace, boiler, or fireplace operation
is extremely conductive and can soon form a static connection between an
antenna and the chimney-flue opening, and across various elements of the
antenna also. This is to be avoided. One poster's advice to keep the antenna
mount "upwind" was well said. Avoiding a chimney mount (on a
working/operating flue) unless other options are not available is even
better.

Best regards,

Jack Painter
Virginia Beach, VA

also posted to rec.radio.amateur.antenna

"Jack Painter" wrote in message
news:NtRLc.6133$_K2.483@lakeread02...

"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm
wrote
Hi,
...
Be advised that carbon build-up from furnace, boiler, or fireplace
operation
is extremely conductive and can soon form a static connection between an
antenna and the chimney-flue opening, and across various elements of the
antenna also. This is to be avoided. One poster's advice to keep the
antenna
mount "upwind" was well said. Avoiding a chimney mount (on a
working/operating flue) unless other options are not available is even
better.

I will not forget this advice !
Thanks

Thierry

Best regards,

Jack Painter
Virginia Beach, VA

also posted to rec.radio.amateur.antenna