The Tatey T Vs an up scaled Telomast! There are several points that way into this. But always remember metal towers effect your radiation pattern! So two big steel towers holding up a T has its own proximity issues and can favor a direction or two. At the end of the day you want smooth radiation in all directions with your site in the middle of the action. I know this isnt always the case but it is what you want if you are trying to get your best bang for your dollar. Dollars, now as MF NAS operators there is usually a budget of ZERO with the same expected return. So we need to keep our heads. Ive long been an advocate of the T and even have one made up ready to go. BUT! There are some people that dont agree with me but I stand firm on the 1/8th rule if you are chasing a mast that works reasonable well. Anything under it the efficency drops off really quick NO MATTER HOW YOU LOAD IT! This rule means you want at least 21 meters for 1611khz in the vertical before you start to load it! You then need to look at the cost of holding all this metal in the air. Another point overlooked is the thickness of the tower itself. Using a tower instead of wire adds to the Q of the aerial. Q is something you want to maximise as this gives better sound on air and the aerial will not be so touchy to tune or when it rains..A quick look at the pic (on nathans post) you will see the T is in bold because they have made it in a cage design. This is for Q and current reasons. All thanks to a little thing called skin effect... Coasting up things for myself. Ive contacted people like Flight Brothers to get costs for towers. They make the light duty winchups the hams like up to 30m hi for 3500. Then if you want a full 1/4 wave at 1611 you need a 44m hi tower and its just cost you 9000 bucks! There is every chance the T will be supported by a couple of 30s but you need to remember the pull to keep the wires tight. Because swinging in the wind changes the tune. So thats back up to 7000 for two and a bigger land footprint when you put the guy anchors out! This is the realization I came to when pricing everything. The light went on and I realized! Yup Tradition a steel lattice tower series fed. Like you see everywhere. So out come the calculators and the aerial modeling software... Some more assumptions. I looked for the best R (Radiation resistance) I could get IN THE AERIAL ITSELF. The less work the ATU needs to do the better. Thats obviously a full 44m tower (35 ohms). So now we come down a bit assuming council is going to really go nuts over anything you ask for! As mentioned before the price difference for a 44m tower vs a 30 m winchup is drastic. Based on price I have settled on the 30m tower. Today Id go with the 30m light duty tower. A bigger version of the telomast idea. The lattice design of the mast helps dont think you can use pipe! So for shear cost its the bigger version of the Telomast Umbrella design. For me these days. Id do a T if the council wanted me to keep under say 20m but it would be a 4 way T. You need to get as much in the vertical before you load it no matter what design it is. But the lattice of the tower and skin effect changes things compared to straight wire. Shear cost you will be seeing me put 30m winch ups everywhere im allowed that height from council. The current design I like takes a little performance hit (slightly less efficient) so it stays on the side of the smith chart where I can use two coils in an L network to match it. According to the maths R 28 - J 32 is what I get on 1692 khz for a 30m winch up with 3 of the top guy wires hotted up for 6.5m. They are at 45 degrees to the mast. Any sharper you lose R and that is not good. If I keep going with the guys to 8m I get R 30 - J 01 So close to resonate its scary. But now the two coil trick doesnt work. You are now spending a lot of money on hi current caps! For those people that know more that me -- is the extra 2 ohms of R worth it? My understanding of the rules says Im only getting about an extra 1-2% efficiency back (and dropping aerial current). The ATU design gets more involved and can be made from smaller wire in the coils. We always have loss in the ATU. So over all my thinking is best to stay with the mast in a spot where the L network can be used. Hence the whole reason for this -- on a budget!
Posted on: Sat, 25 Oct 2014 05:30:33 +0000
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