||Time Line - 1980: Captive Column Dielectric Tower...
|| The finished Captive
Column Dielectric Tower in use. (32k)
NATO had an urgent need for a portable dielectric
(non-conductive) antenna system. According to IRT Corporation of San Diego California,
this tower was needed for testing the EMP (Electro Magnetic Pulse) survivability of
military aircraft around the world (extremely high level EMPs are given off by nuclear
bombs). The tower therefore needed to be both highly portable and dielectric to prevent it
from affecting the test results.
Due to the very stringent specifications required for this tower, IRT was unable to
purchase it from existing tower manufacturers -- conventional construction methods simply
could not do the job. IRT therefore turned to Mr. Bosch and the Captive Column to
fill their needs. As you will see, Mr. Bosch not only solved their problems, but also
produced a unique tower system that greatly exceeded their specifications.
Here are the design requirements submitted to Mr. Bosch by IRT:
"This Firm Fixed-Price Purchase Order covers the purchase of one (1) seventy (70)
foot tall antenna tower, which shall have (1) a minimum 'dead load' capacity of 500 lbs.
and have a maximum Tower Weight of 300 lbs., and (2) be 'field executable' by four (4) men
in a minimum of 8 hours, requiring only hand tools for such erection. Tower is to be
constructed from non-metallic materials with the possible exception of vendor's use of
small metal fittings. Seller is to furnish all materials and supplies required to
fabricate the above units."
Mr. Bosch took these specs and proceeded to produce a Captive Column tower with the
- The tower was 70 feet tall and weighed 70 pounds (1 pound per foot).
- The tower could be erected by 3 men in less than 1 hour.
- The tower could support a load in excess of 500 pounds.
- The tower was completely non-metallic, with the exception of 3 metal turnbuckles at the
base (acceptable to IRT).
- The tower was packaged in two 10-foot boxes when disassembled, reducing the effort
required for transportation.
- The only tool required to erect the tower was a hand wrench to tighten the turnbuckles.
When comparing the delivered product to the IRT specifications, you can see that Mr.
Bosch had eliminated the need for 1 man and shaved 7 hours off of the erection time --
improving on specifications that were already too tough for any other construction
technique to satisfy. The second-generation tower was expected to weigh about 50 pounds.
The following photos show some construction stages of the Captive Column NATO tower.
||Semi-automated Bosch winding
machine wrapping a Captive Column vertical compression element of the NATO tower. (34k)
||Close up of the winding heads.
||Some finished NATO Captive Column
tower components. (30k)
||The tower begins to take shape.
The finished tower consisted of 7 vertical components, 18 radial components, a mylar rope
tension cage, and miscellaneous hardware for assembly. Turnbuckles at the base, weighing
12 pounds, made up a good portion of the 70-pound total weight of the tower. (28k)
||Assembled tower can be held at
any point without bending or twisting out of spec. Billiard balls were used for joints to
provide flexibility under extreme loads. (54k)
||The entire NATO tower fit into
two ten-foot boxes for air transport. The mylar tension cage had to be designed so that it
wouldn't snag. (41k)
||The Fargo North Dakota shop where
the NATO tower was built. (18k)
It should be mentioned here that Mr. Bosch did not go to all of this effort to design
and build just one tower (sold to IRT for $11,000). IRT had told Mr. Bosch at the start of
the project that there was a definite need for towers of this kind, and that IRT would
purchase some more. Mr. Bosch therefore believed that he was in fact building the
prototype for a fledgling business. Although the tower met and exceeded the needs of IRT
and remained in use for the duration of its scheduled multi-year service period, IRT never
purchased another tower. This was interesting considering this communication from IRT
"... I would like to say that IRT is excited about the potentials for this
technology. We are looking forward to working with you in the future in helping to bring
the Captive Column technology to the market place in the form of practical devices such as
this tower." -- Thomas W. Buckman, Ph.D., IRT Staff Engineer
IRT has never offered an explanation for their actions, which put Mr. Bosch out of