[SCCC] SCCC Digest, Vol 49, Issue 26

[Art]

Juan, I neglected to mention there is a fellow right there in your neighborhood who has gone before you on this. Jim Jorgensen AA6JJ, Jim probably has some good ideas for you.

73 Art

Message: 1
Date: Sun, 28 Jan 2007 11:13:55 -0700
From: Art <k6xt at arrl.net>
Subject: Re: [SCCC] SCCC Digest, Vol 49, Issue 25
To: sccc at contesting.com
Message-ID: <45BCE7E3.80205 at arrl.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Juan
The very first decision is "What antennas?" Until you know that, you 
won't be able to guess how much load you'll put on the mast so that you 
can use the calculator K6LL sent you. If they're a stack of 3 element 
yagis for 10-20, a shorty 40, and a 80 rotating dipole that's one 
calculation. If they're 5 element monobanders on 42 foot booms, a 3 el 
40 and a 2 el 80 well, you'll need a bigger mast. Nothing else can be 
known until you choose antennas. Same with the tower. Until you decide 
on your antennas you can't pick the tower.

Or, if you've chosen a tower, then the calcs work the other way from the 
max load the tower will support. Knowing that, you can pick suitable 
antennas, stacking distance, etc. that will not overload the tower.

Fundamentally the least optimum place to start is with the mast, unless 
you plan to buy tower and antennas to not overload the mast, not a very 
good way to do it. Possible, certainly, but not logical.

You might also want to look into Kurt Andress' (K7NV) stress calculator 
YS (Yagi Stress).

21 feet of pipe, if you can find long enough pipe, 4 ft in with an 
antenna out the top is a real torque arm. It will give you fits.

55 feet is not long enough given your signature statement "Lets dx NOW, 
not Later". You'll be doing it later on 40m, just after everyone with a 
72 ft crankup with shorty 40 on top who has a hilltop like yours. My 
advice, worth every penny you pay for it, go for the 72 ft'er so you can 
get that 40 up a half wave. Model a 40 at the two heights, you'll see.

If, like I suspect you'll find, you end up with a 21 ft mast with 8 to 
10 ft inside the tower (forget that 4 ft stuff...), your next angst will 
be antenna interaction. The two choices for a single tower layout are a 
tribander at the top and a short 40 at the bottom, or monobanders 10 
thru 40 stacked. The tribander is a compromise from the gitgo. The stack 
will probably outperform it, but will interact. Take the Alfred E. 
Newman approach, "What, me Worry?" because it's all you can do with one 
tower. Put er up and tune for max smoke.

Well. As I wrote earlier, worth every penny. You must live in a 
sheltered area if you can get away with designing for 50mph wind.

73 Art

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