PSN-L Email List Message

Subject: Re: Lehman design questions
From: "Ed Thelen" ethelen@........
Date: Fri, 31 Dec 1999 20:02:51 -0800



----- Original Message -----

> > Has anyone used a piece of threaded rod for the boom,  or is it better
to
> > stick with an aluminum dowel,  say 1/2" in dia. ?

Keep thinking "center of mass", "center of mass", "center of mass", ...
And you want the "center of mass" as far as practical
from the pivot.  Any mass not as far from the pivot is bad
 - it brings the "center of mass" towards the pivot and
     shortens the period with no advantages gained.

(Let's not get into center of gyration - same principles apply)

So - a hollow boom is good -

And of course the boom and supports must also be
   - stiff (raise its resonant frequency above some cutoff)
   - non-magnetic (you have enough trouble with
       out stray magnetic attractions confusing you further)
  - stable, ...
so aluminum or copper tubing are among the
better choices.

I'm biased of course, my all time favorite
 long period horizontal was made of 1" rigid copper tubing
 soldered on the family gas stove.  Your wife
 should be so understanding and patient.

 A small propane torch is probably technically
 and politically better!




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Larry Cochrane <cochrane@..............>