I would approach it in the same way as mounting a large TV antenna on a
chimney stack, though the method used may vary from country to country how to
achieve this.
In the UK, traditionally we use a galvanised stranded steel band (lashing
wire) that passes around the chimney stack which is attached to an antenna
mounting bracket with "J" bolts to terminate the band and adjust for tension.
Galvanised steel or aluminium corner plates are placed under the wire band at
the other three corners of the chimney stack to spread the load on the corner.
A mast of the necessary length and diameter to mount the antenna is attached
to the mounted chimney bracket with two "U" bolts. With a vertical HF antenna
a heavy duty chimney bracket is called for, or two separate brackets with
separate chimney bands as we used in the early days of TV with large TV
antenna
installations. The galvanised fitting are fairly robust though they can be
replaced with stainless steel stranded wire and "J" bolts if local corrosion
was to be a problem. I use galvanised fittings and paint all potential areas
of corrosion with an automobile body underseal/internal panel rust inhibitor.
In the UK this is product marketed by Finnegan (Hunting Lubricants) called
WAXOYL. This product excludes moisture and dries with a surface skin which
also
discourages the gathering of moisture. Our Volvo station wagon manufactured
in Sweden uses a similar brown coloured product inside it's automobile door
panels. Antenna fittings painted in this way are still removable 20 years
later whilst a normal fitting would be rusted solid after only a few years in
some locations. The moral is if it could rust paint it which I also do with
any
fittings on the antenna itself that could rust living in a rather wet part of
the UK.
In the late 1960's I had an antenna similar to the HyGain 12AVQ mounted with
two "U" bolts on a 1 1/2" (38mm) stub mast in this way with radials attached
to the ground connection on the base of the antenna. If a longer mast is
used the radials could be arranged as guy wires for added strength of the
installation. The methods used depend on the exposure to wind and the elements
at
the chosen location. The same method I now use with a moderate sized VHF/UHF
collinear antenna that occupies the prime position on one of my chimney
stacks. If an external TV antenna were to used and space was restricted it
would be
possible to mount a TV antenna under the HF antenna on the mounting mast. In
my case I do not have this problem living in an old house with three
chimneys stacks to cope with the old situation pre central heating of a fire
place
in every room.
Served my early work experience in the late 1950's in the Radio and TV trade
standing on roofs/chimney stacks to install TV antennas.
Bob, G3VVT
K2 #4168
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