ZL1RS - Antennas

2020 Tower Project


The 'big' tower project - the 'initial plan'

Finally (after too many years), the 'big' lattice tower is going back up. OK, not so 'big' in the general scheme of things, but 'bigger' than what I have had up at this QTH.

The 'initial plan' was for two of the 6.4m lattice tower sections supporting an 8m long rotating steel mast to stack antennas. That was completed in December 2020, but did not work out ... during high winds there was some mechanical resonance between the temporary 6m Yagi and the 8m tall rotating mast section. The Yagi vibrated in certain wind directions (particularly when blowing across the boom) and it seemed that the situation would probably get worse with a bigger antennas (which was the case with progressively longer 2m Yagis on my other rotating mast).

As a result, the idea of an 8-over-8 array for 6m has been abandoned and work is under way on the 'revised plan'.

Below is the work done during 2019 and 2020 on the 'initial plan':

late 2019. The tilt over base foundation preparation. The holes for the tilt base support legs are over 1.2m (4 feet) deep:

early 2020. The tilt base assembly set in concrete. The 'top block' of the concrete base was made much larger/deeper than shown above:

Oct 2020. The guy wire anchor posts were concreted into place with the help of ZL1IU, ZL1RQ and ZL1SG:

Oct 2020. Mounting hardware for the thrust bearing and rotator assembled from recycled materials:

Nov 2020. A square tube 'lever pole' was fabricated from some angle steel that I bought on a whim sometime during the last century!

Nov 2020. A 'ladder rest' made from scrap steel to support the top of the tower when tilted over. This places the rotating mast at a 'nice working height' to attach antennas. The 'lever pole' sections are welded together and ready for bolting to the tilt base.

Nov 2020. The 'lever pole' was bolted securely to the 'tilt base', the tower sections are bolted together and propped up on the 'ladder rest'. Everything is ready for the guy wires and then to swing the 'tilt base' up to meet the flanges on the bottom of the tower legs.

Nov 2020. A rain cover for the thrust bearing, made from a stainless steel kitchen bowl. The 6m Yagi elements and Perspex driven element mounting plates are on the work bench in the background.

Dec 2020. The 'lever pole' was raised. The tower base flanges were then bolted to the tilt base, the 3/8" diameter galvanised steel guy wires were attached (5.5 ton minimum breaking strength), and the tower was then raised with my 'winch' (a 35hp 4WD Kioti tractor!)

Dec 2020. The rotating mast ... this is being assembled with 3m of 74mm diameter, thick walled galvanised steel 'stub mast' coupled to 5.5m of 'double wall' 60mm/48mm diameter gavlanised steel pipes, plus another 2.8m of single wall 60mm diameter galvanised steel pipe. The antennas will be clamped onto the top 7.6m of rotating mast.

Dec 2020. The Aiga rotator and thrust bearing with stainless steel 'rain cover' are in place, with the 'stub mast' ready to receive the 'rotating mast'.

Dec 2020. The 'rotating mast' was fitted to the stub mast and a temporary 6 element 6m Yagi was fitted to the top.

Sept 2021. The temporary 6 element 6m Yagi was removed, the 'rotating mast' was extended about 6 feet longer, and a three-stack of 5 element Yagis for 6m has been installed as an experiment for the next '6m season'.

I still plan to extend the lattice tower and install a different array. Follow this link to see the the 'revised plan'.

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