[TowerTalk] stacking of TH11DX, Discover 7-3

[K4SAV]

I think you need to do some tower loading calculations.  The HDX-589 is 
rated for 16 sq-ft at 70 mph. That's with the load about 1 ft above the 
top of the tower.  You are in an 85 mph zone.  That means the tower 
rating will be reduced.  If you mount the TH11DX one ft above the top 
with the boom support at 3 ft above the top, then the tower rating 
should be reduced to somewhere around 7 sq-ft at 85 mph.  Since the 
TH11DX is 12.5 sq-ft, that single antenna overloads the tower. 

Any antenna mounted above the top of the tower will reduce the rating of 
the tower in a hurry.  Another large antenna above this one would really 
be asking for trouble.

Please don't take my hurried approximate calculations as gospel.  Do 
your own or have a qualified person do it for you.

Why would you want two different antennas stacked close together that 
cover many of the same bands?  That's a recipe for trouble also.

Jerry, K4SAV

ke2d at comcast.net wrote:
> Good afternoon, 
>
> Just about done assembling a TH11DX and Discover 7-3.  I am planning to install them atop a UST HDX-589 tower, and have a few questions regarding the optimal arrangement. 
>
> The TH11DX weighs approx. 88lbs, and the 7-3 weights approx. 98lbs.   Wind load is 12.5 sq.ft. for the TH11DX, and 9.0 sq.ft. for the 7-3.  Should I stack based on weight, or wind load? Anotherwords, should I place the 7-3 just above the top of the tower (thrust bearing), and the TH11DX above it, or place the TH11DX just above the thrust bearing, and then the 7-3 above it? 
>
> Also, how far should I separate the two?  I seem to recall reading 10ft or so, but I really don't want to have this heavy of an antenna (either one) 10ft up the mast if I don't have to.  The mast is the UST M20R reinforced mast, but I believe the inner reinforcement only extends so far up the mast.  Anyone know how long the insert is?   I'm guessing it is only a few feet above the thrust bearing.  Maybe later when I get home I'll slide a tape measure into the mast and try to figure it out if no one already knows. 
>
> The TH11DX's boom support needs to be 2ft above the boom-mast bracket.  The 7-3 needs 5ft for the support cables.   I was thinking of placing the 7-3 just above the thrust bearing, maybe a foot or so, then placing the TH11DX just above the 7-3's boom support bracket, which would be approx. 5ft above the 7-3.  Anyone have any opinion as to this arrangement? 
>
>
> While I am at it, I had two thoughts as to getting the antennas onto the mast. The first is to raise the tower so that the mast is about 12-15ft above ground, then split the booms at their splice points, install the middle 3rd  portion of the boom, then raise a few more feet, install top thirds of the TH11 and 7-3, raise the tower verticle, then rotate the rotor 180 degrees, then lower the tower again, and join the remaining 3rd of the antennas to the mounted booms. 
>
> The other option is to just install the boom-mast brackets on the mast, then raise the tower. Then either rent one of those scissor-like platforms to raise the antennas (and myself) up to the mast brackets.  I also have a neighbor who owns a bucket truck, and he has offered me the use of it.  Anyone use a bucket truck (like the CATV or Verizon van style) to raise a 100lb antenna and 200lb man?    Would you consider that a safe move, or a crazy idea? 
>
>
> Thanks 
>
> Eric 
>
> K2WD 
>
> lk
>