Tower Design Criteria

 

"Someone still stupid enough to build quads".

First of all, It is not a quad. It is a copycat of professional grade broadcast HRS antenna. Well, ok.. yes it looks like a quad, mechanical challenges are very similar to quads, and behaves almost like a quad with some interesting additional properties.

I wrote earlier that I am planning to prove that quads can be built to survive the Finnish winter. I was discussing with a fellow HAM yesterday and he was really suprised to find that somebody is still planning to build quads after so many documented failures. Well.. it is not a quad :)

So I think my plan calls for an explanation.

Background

I started planning this tower project in fall 2011.

I constructed a 2 element beam for 40m band to my current tower. Since the tower is only 15 meters high the performance was clearly sub-par, but I wanted to try it out. The antenna was very nice for short skip contacts, but for DX it was a miserable failure. Further, the 40 beam was way too close to my 20m beam causing distruction in the 20 pattern so I had to make the hard choise to take the 40m antenna down. Never regretted that decision.

I started a lengthy study and computer modelling excercise before the decision was made regarding the tower setup.



I have done literally hundreds of hours of EZNEC modelling of all kinds of beams during past 14 moths. I have consulted people who I consider to be the best in the field in OH-land (people behind the radio Arcala monsters). I have read thousands of pages of material from reference books and from various Internet sources.

Further, I have visited fellow hams and discussed with elmers behind dozens of successful tower setups. They have x-mas trees full of 5 el beams, stacks of 6 el monobanders, logperiodic stacks, phased wires, etc. I put all of those through the EZNEC in order to seach the best possible combination for my criteria. I have made many new friends during this project and I have to say I have met amazing people with incredible antenna systems and stations.

This was an interesting process from idea to setting the criteria, testing the ideas with computer models, finally implementing the prototypes, and test running the antenna setups (for example worked 7O6T, E40VB, 6O0CW with the prototype one cell HRS antenna). For prototyping I took the approach to fail early and fail cheap. Several antennas were shattered in pieces after gusty winds, but that was to be expected. I learned mechanical construction in hard way and the places that are suspectible for cracking.

But I think I am jumping ahead to the conclusions. Lets discuss about the thinking behind the decisions.

Decision Making Criteria for Tower Setup

My primary purpose for this tower is DX, IOTA, and SOTA. The QRP contesting is secondary use, although a very important one.

Must haves:

> 20dB front/back on all bands

beams for 40-10

1.5kW QRO support on all bands

low takeoff angle with beam takeoff control for short skip EU contacts

no compromise WARC bands

mechanically rugged design (gusty winds, frost, heavy wet snow)

wide bandwidth to sustain frost, water, snow

beam control via station automation

Optional and nice to have for this tower:

80/160 bands

ability to construct and maintain antennas without heavy lifting cranes on site

instant 180 degree direction reversal

multi-directional beam i.e. ring rotors or top rotor for one beam to beam multiple directions with one or two tx

power split control between beams on single band

simultaneous use of same multiband antenna via triplexer on multible bands

SO2R support

Other factors to consider

Winter, winter, winter

Small hill on the North side

Space of the lot, other antennas

Cost of the setup

Reference Point

Quite a few DX'ers are using very successfully the 4 el SteppIR antennas.

I decided to put the performance figures of 4 el yagi with same dimensions with SteppIR 4 el with 11m boom as the reference point as well.

So thats it. Not much to ask... :)