[TowerTalk] Determine cost-effective tower height

[K8RI]

On 11/30/2011 7:47 PM, Andreas Hofmann wrote:
> Hi,
>
> I have decided I need a tower to get better antennas up in the air. Thinking about the SteppIR DB 18, 40m 2 el, 20 and up 3el.  Now, my property slopes pretty much in every direction by 5 degrees.  I need to determine a proper tower height without breaking the bank.

I think far too many "over think" this.  I run 160 through 440. I wanted 
the 6-meter yagi as well as the 144 and 440 arrays as high as I could 
get them. I came across a very good deal on a new 100' 45G and figured 
it'd also work well for a 40 meter beam if I ever put one up.  I 
originally put a TH-5 on top.  I worked fine. Optimum? Certainly not, 
but it did well in the pile ups.  Not great stateside, but I like to 
chase DX any way.  So what if the strongest lobe is straight up? At that 
height there are a number of other lobes and some are very low angle.  I 
added center fed, half wave slopers for 75 and 40.  The ones for 40 are 
"outstanding". They generally get the DX on the first call and it's very 
rare to have to call more than twice.  I've changed the one for 75 into 
a fan dipole to broadband it. (IE it's a single band fan dipole) It's 
like a giant bow tie with 4' spreaders on the ends.   160 is a half 
sloper that has a low SWR within the band.

Maybe someday I'll add remote tuners for 160, 75, and 40, but as all my 
feed lines are now LMR-600 there is very little loss even when running 
into a high SWR on these bands.  I use RF Chokes at the antennas and 
where the feedline reaches the tower.

I had to take the antennas down for maintenance due to some large 
migratory birds (Cormorants) that were too heavy for the antennas.

I've mentioned (probably many times) that I'm am adding a 50' 25G on the 
West end of the shop. I figure that's a good compromise for a tribander 
and will actually be optimum some times. With a single Yagi, or 
tribander due to band conditions it's likely to be at the optimum, 
height for one of the bands about 30% of the time.

You can spend a lot of time calculating the best take off angles, but 
those best angles only are the best angles when the band cooperates. I 
believe the article in QST came up with 30% being the time the 
calculated best height was actually optimal

If I were building a contest station and installing stacks I'd certainly 
be interested in antenna heights that would give me the strongest signal 
into various areas with varying band conditions but as I'm not, I just 
go with what ever is convenient.  I've never bothered to run any of the 
antennas through a program to see how they should perform. They work 
very well and I'm happy with that.  Now the thing is to find some help 
to get the antennas back up.

The programs already mentioned will allow you to what height will be 
best most of the time that it can be best. You still have to input soil 
and terrain conditions

73

Roger (K8RI)

>
> I was told I should run a computer program to figure a good height of the yagi for my most important directions/DX locations.  In fact a friend of mine did the same (on a similarly sloping property) and he found out that a 55 foot tower would be similar to a 120 foot tower on a flat ground.   Hence he put up a 55 foot crank up mast and it is rocking.  He forgot the program he used.
>
> So, what tool can I use to find the optimal (not maximal) height of a tower that would work well here?
> Also, the tower would be setting on the side of the house with a metal roof (roof about 15 feet high), not sure if this would matter...
>
> Thanks
> Andreas
> KU7T
>
>
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