Hamtenna … New Station Project

This time HamTenna will see itself as a customer … with a project for the new station that will be born in 2021.

Let’s start with a BigBoy Prosistel rotator … an initial revision and a new pair of oversized gear wheels …

Wind load area 4.1 m2 44.1 sq/ft
Rotating torque 3800 Kg/cm 3300 in/lb
Braking torque 29000 Kg/cm 2100 lb/ft
Vertical load 850 Kg 1870 lb

Work in progress: the rotator has been opened and I have checked the condition of the tapered bearing (perfect), the oil level and the condition of the seals.
No signs of wear were detected.

The external body of the engine and the transmission part was sandblasted, cleaned with a specific 3M product and painted with “thermo 800°C” paint, finally two coats of Plastidip spray were applied.

The pinion of the rotation plate has been greased abundantly and the old ring gear has been removed to be replaced with a larger one.

The electrical contact compartment has also been cleaned and all connections have been checked.
The old 7x1mm cable has been removed and will be replaced with a new fitting up to the control box located near the rotor.

BigBoy restored and tested :

 

What about antennas ?

The project will start with the HF Tower-1, a 9mh tower with coax elevator for EME 144MHz and a small tower for EME 430MHz.

Tower-1 will be 29mh base rotating and it will support the main antennas for 10/15m, at the top a dynamic 10-40m which in the future will remain as a secondary antenna but which in the meantime will make onair  the bands 10/12/15/17 /20 (3 el) and 30/40m (rotary dipole)…  In addition, a 3el fullsize 30m yagi will be installed at the middle part of the tower.

  • 15m 7/7 : two 7el monoband (15m boom each) yagi will be stacked, a stack-match will allow the selection A, B, A+B.
  • 10m 8/8 : two 8el monoband (15m boom each) yagi will be stacked, a stack-match will allow the selection A, B, A+B.
  • 30m 3el fullsize monoband beam
  • Ultrabeam UB-50 service yagi at the top (29,5m agl)

7/7 – 15m

The single 7-element monoband for 15m was modeled by calculating the real position in the stack.
The antenna will have a boom of just over 15m (15.57m to be precise) with a reflector of about 7.6m and an element taper of 35-30-25mm.

The upper antenna will be positioned at 24.5mh while the lower one at 12mh, this position is partially constrained by the position of the rods but still provides a spacing of 12.5m between the two yagis.

The simulation, as you can see from the image below, provides, in stack (ie in stackmatch position A + B), a gain of 18.5dBi at an elevation angle of 9,3deg at the upper antenna.
The F/B ratio of the stacked system is 25.04dB.