[TowerTalk] Summary: Open Sleeve Info

[force12@interserv.com]

Fellow Tower Talkers:

To make sure the development record is straight, the comment from Mr. Cox 
relating to the basic design of the C-3 open sleeve system is not quite 
correct.

The original open sleeve was developed in about 1945, maybe 1946 by Dr. J.T. 
Bolljahn. It was both a broadbanding technique and also a two-band feed system 
that was used as a two-band dipole.

In 1982, Mr. Cox added traps to the center driver of a basic open sleeve to 
achieve excitation on 3 bands. The center driver operates on 20 and 15 mtrs and 
the adjacent elements operate on 10 mtrs. This trapped 3-band system was 
used in the Explorer 14.

The Force 12 enhanced open sleeve system does not use traps to achieve more 
than two band operation. We went back to the efficient, original open sleeve 
system and improved the invention to excite more than two bands (without 
traps). This covered about 2 1/2 years of effort. During that time, the 
two-band system was utilized on a wide variety of antennas.

Some of these duo-band antennas were stacked horizontally on the same boom 
to achieve 4 band operation with two feedlines. Side benefits from this 
configuration are that the rear antenna (lower in frequency) is enhanced 
slightly from the presence of all the (higher frequency) elements ahead of 
it. The main 4 bander is the Force 12 4BA, which is a 24' boom and covers 
17-15-12-10 with true monoband antennas (and gain). We aded a 3 element 20 mtr 
Yagi behind it and made the 5BA, So, on a 32' boom, one has all 5 bands.

One of the duo-banders that was unique was the N1217, first produced in 1992. It 
was originally on a about a 15' boom and is actually a pair of 3 element Yagis, 
one for each band. They overlay each other, with the 3 element 12 mtr Yagi 
inside the 3 element 17 mtr Yagi. It has a 3 element open sleeve (two-band) 
driver in the center. The unique aspect of the N1217 is that normally the 
director(s) of the lower frequency antenna cannot be placed in front of the 
common driver. In this case, however, they co-exist just fine. Another technique 
for being able to have director(s) for the lower frequency band out in front is 
to also "sleeve" them. For example, a 17 mtr director could be "sleeved" with a 
pair of 12 mtr directors, which would render the 17 mtr director "invisible" to 
the 12 mtr director portion of the Yagi. We have done this on several test 
antennas for vaious band combinations. To conclude the N1217 development story, 
the boom was expanded to 18' in 1994. This was done primarily to improve the 
natural balance point, as there was an internal counter weight at one end of the 
boom and by expanding the boom and re-arranging the elements, the balance was 
improved.


Force 12 continues to work on more designs using the efficient open sleeve.

If you have any favorite combinations, let us know!! They are probably already 
available.

		73, Tom, N6BT
		Force 12 Antennas and Systems





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