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Re: Tower Idea



Les,

I am in the process of doing my own tower arrangements.  I'm waiting for
the building permits from the county to move forward.  My comments are
based on my recent discussions with local engineers and hams who have
installed multiple, large (130'+) towers in the Albuquerque area where we
regularly have 50+ mph winds and have seen winds up to 75mph.

Do your own research and find your own trusted sources for information.
If you have been reading tower talk mailing list or searching the web, you
will find that no one can agree on everything about tower installations.  I
suspect many who read this posting on the BB list will question my own
findings.  Towers installations is still an art, many of the ideas that 
people
come up with simply have not been around long enough to pass the test
of time. 

BTW, if anyone does disagree with my comments, please let me know.
I'm willing to learn from those with experience and good arguments.

My notes are below...

sco@sco-inc.com wrote:

> I would like comments on the following proposed idea for a tower 
> arrangement:
>
> US Tower TX-72 with motor drive and crank over (72 feet in height plus 
> 10 - 15 feet of mast above the top of tower).
>
The US Tower specs specify their wind load based on the installation
of the antennas less than 3ft from the top of the tower.  If you install
above 3ft the wind calculations have to be reconsidered, especially if
installing a long mast and mounting at the top as you are.

I had originally figured a 55' TX-455 with a 15' mast (total 65').  One of
my engineer friends did the calculations and said that I was within 80%
of the specified wind load of the TX-455 if I mounted my Force-12
C4-SXL at the 3ft mark on the mast.  He strongly suggested I move up
to a HDX-555 - $1K more but worth the over engineering.  I went from
25sqft of wind load to 35sqft - remember that is at the original 50mph
wind expectation.  The wind load capacity of most towers quickly
diminish as the wind speed increases.

You might want to take a serious look at the HDX version of the 72ft
tower.

> M2 rotor to turn the mast.
>
The M2 OR-2800 is a very good rotor.  If you are buying new or
used be sure you are asking for the DC version.  It has the new key
assembly that will not break teeth.  If you are buying new be sure
to ask the vendor which you are getting, many are still selling the
older AC version.  Most of the used OR-2800s I have seen for sale
are the older AC versions, many with broken teeth when you ask
the sellers.

I have opted to go with the Alpha Spid rotor (www.alfaradio.ca).
What sold me on it was the price (~$850 USD), the double worm
gears (no need for a break), the DC motor, and the fact I can over
rotate more than 360deg if needed.  If I find I need more power to
turn a large array in the wind, I can upgrade the power supply
feeding the rotor motor from 12v to 24v.  I have confirmed with
Alfa Radio that it will fit in the top sections of the TX and HDX.

> Force 12 XR-6A  (10-40m Yagi on a 18 ft boom) mounted about one foot 
> above the top of the tower.
>
> Yaesu G-5500 rotor mounted "pole style" at the top of the mast. It 
> would have my short M2 yagis for 2m and 70 cm plus dish for S Band.
>
Which M2 yagis are you purchasing?  Both of the ones I am mounting
on my 30ft satellite tower have 18ft booms.  Make sure you can clear
the XR-6A when rotating past 90deg elevation.  You have to figure
in the feed line if it will be hanging from the back of the yagi.

Again, that's a lot of wind load way above the tower.  Make sure you
have an engineer do the calculations to see if the tower can handle it.
You should also consider a chromolly <spelling?> mast.  Money
spent now is cheaper than replacing a failed tower or mast and
damaged antennas.

> If I put the satellite array on the HF tower there will be at least a 
> 150 ft (min) cable run to the tower from my shack, plus another 50 
> feet up the tower.
>
> This combination would give me at least a 10 ft maximum separation 
> between the antennas. Should be fine then with no interference 
> problems for the Force 12 or the satellite array (since it would be on 
> the top). Since the tower would be a crank over i should be able to 
> get to the satellite array to do adjustments. The M2 rotor is very 
> very strong and dependable and accurate so there would be no problem 
> to turn the array for HF work or have it stopped at a known heading 
> for the satellite rotor (G-5500) to take over when i wanted to do 
> satellite work.
>
> Is this a practical and workable approach?  I do NOT want to use the 
> G-5500 to turn my HF antenna because I have my HF and satellite 
> stations in two separate desk areas of my "ham shack". plus I do not 
> like the look and feel of the G-5500 for HF work. Therefore that is 
> not an option. I either do the above or need to put up two separate 
> towers, one for HF and one for satellite. Because of the issues with 
> my trees (I am in a forest, it looks like) that would require at least 
> an 80 ft+ tower (to clear my trees) for satellite work. Has anyone 
> pole mounted a G-5500 small satellite array on a 10 -15 ft mast at the 
> top of a 72 ft motor driven crank up/crank over tower?
>
I opted for two towers.  The 55ft for HF and 6m, the 30ft for satellite.
The satellite tower is just tall enough to clear the trees and to allow
the M2 antennas to rotate freely.

I initially had factored in the raising fixture to allow me to tilt the 
tower.
It became obvious that the raising fixture was less useful since I do not
have space to tilt the tower.  Fortunately, I can reach the top of the
tower when in the down position from the top of my roof.

> If this can be done it will save me at least $4-7,000 plus I will have 
> a motor drive on my HF tower (which i would not do if I must buy two 
> towers).
>
My estimates put the project cost for both my towers at around
$8K.  This is $1500 more than my initial estimation.  The 55ft
tower is all new gear, the 30ft tower is all used (tower and
AZ/EL rotors).

I know this is a controversial subject, but have you considered a
ground system?  Here in NM it's not a case of "if" or "when"
I will be hit by lightning.  It's more of a case of how many times
a year I will be hit.  I have spent quite a bit of time discussing
with experienced hams and engineers about how to protect
my station.  Due to the close proximity of my two towers (less
than 20ft apart) I am tying the ground systems together.  There
is a certain amount of protection offered by the 55ft tower for
the 30ft tower.  I am not counting on this and putting in a
ground system for both towers with ground radials and multiple
ground rods.  Due to the poor soil conductivity here in NM I
am doping my trenches.

If you opt for a good ground system you might want to ask
around your local ham scene if anyone has an electric hammer.
Our local FM group has an electric hammer available to
club members.  With the hammer, you can drive an eight or
ten foot ground rod in three to four minutes.  The hammer
will have enough force to bend the rod around obstacles
(large rocks, etc.) or punch through them (smaller rocks,
roots, etc.).

Be sure to cadweld your ground rods and ground wires.
Compression fittings will fail over time.

If you want more information about how I am doing things,
you can checkout my tower project page at my web site at:

http://www.pascal.org/wiki/space/Ham+Radio/Tower+Project

I have notes that I have gathered form some of my research
there, and will continue to updated it as I learn more.


-Freeman, N5FPP

> Les
> W4SCO
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