[TowerTalk] Antenna stacking and boom truss questions

[SPWoo]

Hi All,

I'm new to the group.  I wish to get your opinion on a few ideas that I have.

- From an electrical point-of-view would it be better to have a 40m yagi above or below a tri-bander on the same mast?  The antennas are a Bencher Skyhawk and a F12 D240.  From N6BT's book it says the lower frequency antenna should be below the higher frequency one as you don't want the lower frequency antenna to act as a reflector on the higher frequency antenna.
- Will a boom truss improve the wind survivability of my antennas?  My intuition tells me that a boom truss only supports a vertical load (i.e. antenna weight plus ice weight) and not a horizontal force generated by high winds.  I'm located in CO and I don't get ice here, but I get plenty of wind.  Also, it seems like the boom truss itself will add to the antenna wind loading.
- I'm using AntennaMast Excel spreadsheet to calculate the bending moment on the mast.  What antenna wind loading figures should I use?  Bencher advertises the Skyhawk at 8.5 sq. ft.  This is probably for an effective area.  Someone else in TT has calculated the projected area to be 12.2.  Bencher has not yet responded to my inquiry.  I contacted Mark Hooper at F12 and he told me the projected area for the D240 is 5.82 sq. ft.  So I assume this is the number to use for AntennaMast along with a Cd of 1.2.
- Which direction should the antenna be pointed to maximize wind survivability?

Thank you for your time.  73.

 

Jonathan Woo, W6GX