On 11/30/2011 7:47 PM, Andreas Hofmann wrote:
> 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
> 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
> 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...
> TowerTalk mailing list
TowerTalk mailing list