> Roger (K8RI) wrote:
>> Jim Brown wrote:
>>> I asked a colleague who builds a lot of commercial two-way
>>> installations where I could find 2-inch hot-dipped galvanized mast
>>> material locally. He suggested that I use 1.5-inch rigid steel conduit.
>> There are two types of rigid steel conduit. The one is like schedule
>> 40 pipe and the other (EMT) is thin wall.
>> The heavy conduit like we used in industry is soft like water pipe,
>> but still fairly strong. Then there is thin wall or EMT which would
>> probably work IF the antenna is mounted right at the top of the
>> tower. I would not want to mount the antenna any distance above the
>> top of the tower due to the leverage or angular moment generated
>> particularly due to wind load.
>> Roger (K8RI)
> I've used EMT as a (poor but expedient) structural material for things
> like tents and geodesic domes..
> here's my observations:
> a) It's crummy quality steel and highly variable in material
> properties to boot.
> b) It has a very obvious weld, which protrudes variably into the middle
> c) It bends once or twice, if properly jigged and supported (after
> all, this is what it's made to do)
> d) it cracks along the weld, or the ends, etc. Don't expect to be
> hammering the end flat to make a flange you can bolt through. Or, at
> least, don't expect that flat end to be pretty and not cracked.
> e) it's quite malleable.. not at all springy, so if you load it, it
> bends, and stays bent.
f.) It won't last long out in the weather.
I've used it to build relatively small H-frames for UHF quadrature
arrays about 10' x 10'.
They rust almost as fast as cad plated bolts. OTOH they still last quite
a few years if given a good coat of epoxy paint while still nice and clean.
> On the other hand, it's incredibly cheap. So for a field expedient
> mast or something like that, I'd use it again. Just don't expect it
> to be rugged and long lived. You could throw up 30-40 feet of 3/4" or
> 1" EMT with some lightweight rope guys for a few bucks.
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