[amsat-bb] HOWTO: Insulate the Arrow's elements

[Majdi S. Abbas]

	I know there has been some discussion here in the past on
Arrow modifications -- specifically, either electrically lengthening
the elements, or insulating them from the boom.

	I opted to try to insulate the elements from the boom, rather 
than lengthen them.  This was mostly due to my concern that it would be
hard to ensure an electrically solid lengthening using commodity hardware.

	One possible approach:

	Either re-drill to expand, or ream out the existing holes in
the boom, and install nylon bushings through both sides, possibly placing
a little epoxy on them, to make them a permanent part of the boom.  Then
install the elements as normal.  This would make for a nice finished 
product, but would require 20 bushings, which were in the range of 0.60-
0.70 USD each at the hardware store.  This makes it the most expensive
option.  I opted for a much less expensive option using 1/4" neoprene 
bibb washers, of the type used in compression fittings (check the 
plumbing supplies aisle -- I was able to procure 25 of these washers for
$3.49.)

	I did make one observation about the boom itself -- it is exactly
the width of a standard roll of 3M vinyl electrical tape.  

	Given this, with the use of tape, it should be possible to use 
insulating washers.  Here's how to do it:

	Insulate the boom from the elements by removing the #8-32 
threaded rod from each, and carefully wrapping 1 1/3rd turns of vinyl
electrical tape around the center.  Stretch the tape somewhat as you do
this, and then mold it into the threads in the rod using your fingers.
Removing the threaded rods entirely is necessary to ensure they are 
centered, or you will have trouble getting the elements to fit once
the insulating washers are in place.

	Once this is done, carefully install it into the boom, rolling 
t in the direction of the threads (and tape) to avoid damaging the tape.
It is a tight fight, but it is possible to do so.  You should be able to
see the tape just barely protruding from both sides of the boom.

	Install a 1/4" neoprene bibb washer (nylon washers could also be
used, but those were $0.39 ea, and my goal was to keep this under $5) on
each side, and then reinstall and tighten the elements.  
	
	If you have the split boom model, you may have some trouble with
the 70 cm element that joins the halves of the boom.  You might need to 
ream out or file the holes in the copper tubing inside the boom to get a
tape wrapped threaded rod insert to fit without disturbing the tape.  
Worst case, this could involve drilling out the blind rivet, removing 
the copper insert, expanding the holes and then deburring them, and 
then reinstalling it.  If you don't have a deburrer, a large enough
drill bit would do.  If you don't have a blind ("pop") riveter, you 
could reinstall it using a small nut and bolt.

	The entire process should take about 15-20 minutes.  Total cost
was $3.49 for the 1/4" bibb washers and a few inches of electrical tape,
which I had on hand.  Even with tax, this is less than a $5 modification.

	Unfortunately, I've loaned out my digital camera for the day, so
I don't have any pictures of this modification, but it's pretty straight-
forward.

	I hope this has been helpful to someone who was considering this
but wasn't sure what they needed from the hardware store.

	73,

	Majdi, N0RMZ