In a message dated 97-11-14 00:46:48 EST, firstname.lastname@example.org writes:
> For years I have used Schedule 40 1.5" (1.900" OD) galvanized water pipe
> for masts. I think there cannot be a problem if the antenna is within a
> couple of feet of the top of the tower.
Hi, Stan --
Glad to have you on-board TowerTalk. Enjoyed our chance to spend some
time together at the WRTC96. Start making plans for WRTC2000 in Slovenia -
it'll be the party of the millenium!
The key here is "within a couple of feet". Schedule 40 water pipe has
very little (if it's rated at all) yield strength; somewhere around 25-35,000
psi yield strength at the most. It doesn't take much antenna and wind to
exceed that figure particularly if you have several feet of bending moment.
> If I am stacking antennas such as my little Cushcraft 2 Element 40 which
> is about 10-12 Ft above a 4 Element 20, I'll telescope a Schedule 40
> 1.00" galvanized water pipe inside the 1.5" one and drill and pin them
> near the top with 1/2 inch bolt. This makes for a VERY heavy mast that
> I think (no basis other than 30 years of no problems) will stand a lot
> of wind/flex. The last time I checked I couldn't find Schedule 80 that
> was galvanized. Besides the 1" inside the 1.5" appears to be stronger.
> I would not put a very large antenna very far above the top of the tower
> regardless of what mast I was using and I definitely wouldn't have an
> installation that required that I worry about which way the wind was
> blowing relative to the direction of the antenna...
You've got two things going for you. First, having another pipe inside
does add to the total strength. Second, the whole state of Arkansas is only
rated at 70 MPH, the lowest rating they give. For more aggressive
installations and places where the county wind speeds are higher, I would NOT
suggest water pipe for a mast.
73, Steve K7LXC
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