[amsat-bb] Re: Mast strength??
Edward Cole
kl7uw at acsalaska.net
Thu Nov 22 14:47:02 PST 2007
OK,
Well, if I assume your fiberglass boom is about 1.5 inch diameter to
max opening of the G5500, maybe you could find some alum tubing that
would just slide over the fiberglass for a nice fit. One trick that
is used is to slit the end of the tubing with a hack saw about 1/2
inch in and place a hose clamp over the end to clamp it tight to the
smaller (fiverglass) tubing. I did this with a 70-MHz yagi to extend
the elements to work on 6m.
Aluminum sched-80 tubing should be strong enough for your mast if you
are going to shorten it a lot. As I mentioned my setup uses about
8-feet above the tower. BTW I was quoting from a standard chart for
1-1/2 inch shed-80 steel pipe when I suggested 1.9 inch O.D. But a
shorter mast of aluminum will probably be OK, but still go with a
thick wall (thus my recommendation of sched-80).
You are thinking 16-foot mast, 4-foot inside tower, 12-feet above
tower. Assume 6m is attached at 1-foot above tower this leaves
11-feet spacing between antennas when all are at zero
elevation. That is way more than needed. The satellite booms extend
~9 foot so when elevated at 90-deg. they will still be 2-feet above
the 6m antenna. OK that is max height I would try.
But if you use 10-foot of mast, 4-foot inside tower, 6m antenna
1-foot above tower you will still have 5-feet separation that is 1/4
WL on 6m. You would need to extend the crossboom so that as the sat
antennas elevate they will pass outside the 6m elements. At 90-deg.
elevation your sat antenna booms would extend about 4-feet lower than
the height of the 6m antenna. Interaction between them ought to be
minimal. Also since the time that satellites spend above 80-deg.
elevation is very small this is not that much of a compromise.
So this should give you some ideas, GL!
At 01:13 PM 11/22/2007, Stargate wrote:
>Ed,
> That's an idea I had not thought of. Extend the satellite
> antenna's out to
>the point where
>they are past the ends of the 6M antenna. Hmmmm, I already have a fiberglass
>crossboom that came
>with the trade I made a while back and was planning on using it, but your
>idea gives me some more
>thinking to do. Thanks
>
> The satellite antenna's turning radius is only about 10' so
> a mast 16'
>would give me 4'
>inside the tower and still allow for 1/4 wavelength of distance (at 145mhz)
>between the 6M antenna
>and satellite antenna's at 90 degrees vertical.
>
> Your idea would certainly be stronger and may be the way I
> end up going,
>but I still wonder
>what grade of tubing I would need for that length and wind load.
>Pipe is a no-no, from what I have read since it is not really made to
>support lateral loads,
>and tubing is rated in lateral load or bending moment. Also pipe is measured
>in inside dimensions
>rather than outside dimensions. A 2" pipe is not 2" outside diameter.
> I'm still not sure what to use. I would think aluminum of
> the correct alloy
>and thickness would suffice but
>I would hate to see it laying on it's side one day:-(
>Your idea may be cheaper in the long run due to the strength it would have.
>
>Any other ideas from anyone?
>
>Thanks,
>RoD
>KD0XX
>
>A good friend will come and bail you out of jail,
>A TRUE friend will be sitting next to you saying.....
>
>
>"DAMN THAT WAS FUN"
>
> > -----Original Message-----
> > From: Edward Cole [mailto:kl7uw at acsalaska.net]
> > Sent: Thursday, November 22, 2007 4:16 PM
> > To: stargatesg1 at verizon.net
> > Cc: amsat-bb at amsat.org
> > Subject: Re: [amsat-bb] Mast strength??
> >
> >
> > Rod,
> >
> > Your dimensions of 2-inch diameter (I assume outside diameter) with
> > 0.25 inch wall thickness is closest matched to standard sched-80 pipe
> > with 1.9 inch O.D. and 0.2 inch wall. In steel pipe this weighs 3.36
> > lbs per foot length. Your 20-foot piece will weigh 67 lbs. That's a
> > lot of weight and wind load to be supported by only 2-feet inside the
> > tower! Add the weight of the rotator, crossboom and antennas and I
> > think you will NOT keep it up in 70 mph winds.
> >
> > Guessing that the element length of the 6m yagi is about 1/2
> > wavelength (about ten feet), why don't you consider using a wider
> > crossboom so that the satellite antennas clear the ends of the six
> > meter yagi when you elevate them? If the 2m antenna is mounted in
> > the "X" configuration you need about 1/2 of 1.4x40 inches beyond the
> > six meter antenna width to mount your 2m antenna. Maybe make this
> > about 1/2 of 1.5x40 = 15 inches. A cross boom of 12.5 feet should
> > do. Since the satellite antenna only comes close the six meter
> > antenna at extreme elevation angles spacing needs not be any more
> > than that. You can then lower the vertical mast requirement by half
> > and end up with a lighter and more engineering stronger setup.
> >
> > With this setup your roughly 18-foot antenna boom ends will drop to a
> > foot or so below the level of the 6m yagi at elevation=90. If you
> > were to lower the most more then the satellite antennas would be
> > correspondingly lower at 90-degrees (min mast spacing between 6m and
> > satellite antennas is about 5-feet). I think this would be a better
> > design than having so much exposed unsupported mast with heavy top
> > load. I am putting up my satellite antennas on a single Rohn-25
> > tower top section with about 8-feet of 2-inch aluminum mast and
> > 5-foot crossboom. I will have the same rotor and UHF yagi, and the
> > KLM-22C (very similar in size to M2CP22), plus a 33-inch dish. All
> > of this system survived several years use at my old QTH where is was
> > supported by a 3-foot RS TV tripod tower. You can see old photos of
> > this on my webpage:
> > http://www.kl7uw.com/sat.htm
> >
> > You should measure your antennas to be sure of the crossboom length
> > and add enough so that antenna clamps have sufficient boom to clamp
> > and antenna elements clear. A metal crossboom will work (regardless
> > of what you may hear). If you worry about sagging of the crossboom
> > this is easily strengthened by making a truss from rayon cord and a
> > couple 1-inch pieces of tubing mounted either side of the elevation
> > rotor. Probably 2-foot long would suffice. Use small turnbuckles on
> > the cord to tighten . This method has been used in the past to keep
> > very long yagi booms from sagging.
> >
> > Good Luck!
> > Ed - KL7UW
> >
> > At 10:13 AM 11/22/2007, you wrote:
> > >Hi all,
> > >
> > > I am installing 20' of Rohn 45 with a flat top from Normsfab
> > >and a Yaesu GS-065 thrust bearing.
> > >
> > >The lower end of the tower is already figured out but I'm not
> > sure of what
> > >strength 2" mast I need.
> > >
> > >
> > > All this short tower will be supporting is a 3-4 element 6M
> > > homebrew beam
> > >just above the bearing on the tower,
> > >as well as, the elevation portion of the Yaesu G-5500 rotor with 8'
> > >fiberglass cross mast, and M2 2MCP22, and
> > >436CP42UG beams on each end of the cross boom.
> > >The 2MCP22 is 2.5 sq ft wind load.
> > >The 436CP42UG is 2.0 sq ft wind load.
> > >I'm not sure of the WL for the rotor and 6M beam.
> > >
> > > The mast will have to be at least 18'-20' long to give 2-3
> > > foot inside the
> > >tower to the AZ rotor and
> > >enough sticking out the top to give 1/4 wavelength (at 2M)
> > spacing between
> > >the satellite antenna's
> > >and the 6M beam.
> > >The satellite antenna's are close to 20' long and mount from close to the
> > >center so I need at least
> > >10' (+1/4 wavelength) above the top of the 6M beam.
> > >
> > > I'm not an engineering type so I thought I would ask on
> > here. What
> > >thickness
> > >and material would the mast need to be to support this.
> > >
> > >I am thinking T6061 aluminum, .25" thick wall, 2" outside diameter mast.
> > >
> > >I live in a 75mph wind zone.
> > >
> > >
> > >Any help would be much appreciated.
> > >
> > >Thanks,
> > >73's
> > >RoD
> > >KD0XX
> > >
> > >A good friend will come and bail you out of jail,
> > >A TRUE friend will be sitting next to you saying.....
> > >
> > >
> > >"DAMN THAT WAS FUN"
> > >
> > >_______________________________________________
> > >Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> > >Not an AMSAT-NA member? Join now to support the amateur
> > satellite program!
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> >
> > 73,
> > Ed - KL7UW
> > ======================================
> > BP40IQ 50-MHz - 10-GHz www.kl7uw.com
> > 144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
> > DUBUS Magazine USA Rep dubususa at hotmail.com
> > ======================================
> >
73,
Ed - KL7UW
======================================
BP40IQ 50-MHz - 10-GHz www.kl7uw.com
144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
DUBUS Magazine USA Rep dubususa at hotmail.com
======================================
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