I bought the TW-32-XL beam (2 el on 30, 17 and 12m) from Mosely to gain directivity on 30m.
I am not operating on 30m much and beverages provide a receive directivity, but it would be nice to have a strong signal in case a rare DX comes up. For the upper WARC bands my 5 band Spiderbeam @ 12m has 2 el on 12 and 17m.
TW 32 is to be mounted on a 120’ (36m) high Rohn 45G. However, it is not obvious how to do it as various options have pluses and minuses.
Option 1. Stacking on top of the tower, 3m over the GXP 17-4 beam.
The mast consists of 2.4m 2-inch AL mast telescoping within the 2.5 inch mast that hold GXP 17-4. The TW antenna can be hoisted in pieces and reassembled on top, but this is not easy and can bend the masts. The antenna can be hoisted up complete if GXP 17-4 is temporarily twisted although the range of twisting is limited by horizontal guys of 17-4. Even if the TW beam is hoisted up, pushing the 15kg antenna up the telescoping mast would not be easy.
Once on top, the antenna would be very hard to maintain, an importnat factor for an antenna with traps. Also, it would add a substantial wind load plus an extra load for a rotor that many say is already underpowered for GXP17-4.
Option #2. On top of the tower, but just the driven element.
Hoisting one element would be easy but no directivity although the height (39m or 130’) would partially compensate.
Option #3. Understacking below the tower
W1XT came with the idea of under stacking, where the second mast is attached to the main mast by a sidearm pointing down, and the antenna is installed below. AA4NU understacked bigger 40-2CD without any problem.
See W1XT paper.
Understacking at 33m (110’) is relatively easy and would allow for easy maintenance. But it would add some wind load to the mast though less than overstacking, would add load to the rotor, and could somewhat interfere with the 4 sq for 160m. The 4 sq has ropes attached to the tower at 35m (117ft) and these would have to be lowered by 2-3 m with some, perhaps little effect on performance. While the 30m operation is marginal for me, the 4 sq for 160 performs greatly, making all loaded towers with kilometers of ground wire a joke.
Option #4. Swing arm mount
The antenna can easily be side mounted over the second guy (23m or 75’) wityh swing arm mount allowing up to 300 degrees rotation – ask K4IDC for a design.
Screenshot
The extra cost would be a) side mount, b) rotor and c) rotor controller. Altogether too much hassle.