[TowerTalk] Homebrew 30m beam

[Joe Subich, W4TV]

On 5/2/2024 11:26 AM, JVarney wrote:
> The elements in the 40-2CD are undersized, they start at 1.25 in at
> the feedpoint but should be 1.50 in. minimum.
The 402-CD/XM240 has held up rather well for many years other than
in certain extreme conditions (e.g. hurricane coasts, heavy icing).
Replacing the coil/cap hat assembly with its weight at the end of
the element with 36" of tubing should reduce the element stresses
and the overall survivability can be enhanced by double walling the
first 36" of the 1.25" center sections.

> If it were me I'd go 40% shorter, say 28 ft wingspan and insert an
> air coil with Q=800 or better in the middle.

It would not be necessary to be that aggressive with the shortening -
30% shorter - e.g. a 20 meter element - would be fine and reduce the
the coil requirement over a 50-60% size element.  36 foot elements
starting at 1.25" with a double walled first section would be more
than sufficient and could be easily sourced from surplus 402CD/XM240
elements.

73,

    ... Joe, W4TV

On 5/2/2024 11:26 AM, JVarney wrote:
> I don't know, 46.3 ft wingspan unsupported is
> too floppy and droopy for my taste. The elements
> in the 40-2CD are undersized, they start at
> 1.25 in at the feedpoint but should be 1.50 in.
> minimum. That could be addressed with an
> element support truss, but that adds
> mechanical complexity.
> 
> If it were me I'd go 40% shorter, say 28 ft
> wingspan and insert an air coil with Q=800
> or better in the middle. That would provide a
> more robust structure while being efficient
> with minimal losses, probably less than
> 0.5 dB.
> 
> 73 Jim K6OK
> 
> Joe W4TV wrote:
>>> The elements are already 22+ feet long.
>>> Replacing the 18" coil with a 36" +/- section ...
>>> would be the only mechanical changes to the
>>> elements ...
> _______________________________________________
>