[time-nuts] Freestanding mast

[k6rtm at comcast.net]

I've a Symmetricom(HP) 58532A antenna on a six foot mast -- T6061 aluminum schedule 40 pipe. Not as cheap as cast schedule 40 from the home store, but a lot lighter! The previous mast was a length of cheezy Radio Shack antenna mast -- thin wall stuff. The mount for the 58532A wanted larger diameter schedule 40. 

Oh, that mast also supports a Davis Instruments Vantage Pro2 weather package -- the GPS antenna is on the mast, which is between the rain collector bucket and the anemometer mast. The rain bucket is due south of the GPS antenna, and below the GPS antenna horizon. While the anemometer mast holds the anemometer assembly up a few inches, it's due north, so it's in the region where the GPS birds don't go anyway, and is below the elevation mask angle as well as the angle at which the birds appear. Life is full of compromises... 

We get very little snow and/or ice here, but usually have storms in the winter with 50+ MPH winds. A 10 foot stick of the cheezy thin wall held up the weather instruments for a number of seasons with no problems. The 58532A doesn't add appreciable cross section in comparison to the rain bucket. I don't anticipate problems with the larger diameter mast, and would expect a 10 foot length to be quite stable. T6061 aluminum is a favourite for antenna construction. (I went with the six foot length as it was available as scrap.) 

Separate 24 hour antenna surveys with the weather sensors six inches or so below the GPS antenna, and then with the weather sensors at their nominal operating height with respect to the GPS antenna did not show easily observable differences in tbolt operation. 

73 de Bob K6RTM in Silicon Valley 

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Message: 2 
Date: Thu, 02 Sep 2010 20:46:00 -0400 
From: "Charles P. Steinmetz" <charles_steinmetz at lavabit.com> 
Subject: [time-nuts] Freestanding mast 
To: Discussion of precise time and frequency measurement 
<time-nuts at febo.com> 
Message-ID: <20100903004603.B222311B868 at karen.lavabit.com> 
Content-Type: text/plain; charset="us-ascii"; format=flowed 

I'm curious what the best freestanding mast is for a timing antenna 
(think Lucent timing antenna or marine "mushroom" GPS antenna -- 
light and pretty small). The mast would have its highest support at 
rooftop or chimney-top level, and could extend from there as far 
downward as the ground with additional supports as required. Should 
be able to survive at least Category 2 winds and heavy snow and ice. 

What reasonably available mast material no more than, say, 3" in 
maximum cross-section would allow the most vertical extension above 
the highest support, and how much extension would that be? I'm 
thinking 10 feet of 2" or so thin-wall steel tube may be OK, but 
beyond that I don't know. Tubing is probably not the optimum shape, 
but I assume the availability of other engineering shapes (say, "+" 
cross-section) is likely to be limited. 

Ideas? 

Thanks, 

Charles