[QCWA] Re: QCWA Digest, Vol 11, Issue 8

[Walter Maxwell]

Bill Pasternak's mention of WSM's diamond shaped tower recalls an
interesting technical issue. The deviation from a uniform cross section of
the tower caused a non-uniform current distribution along the tower that
resulted in an undesirable elevation pattern of the radiation. This was one
of the many tower problems that were solved by Dr. George H. Brown, of RCA.
He modeled this tower with a scaled-down version and measured the radiation
patterns with different length-to-width ratios. From these measurements he
determined that the only way to obtain a uniform current distribution was
with a tower of uniform cross section.

Collaborating with John Lietch, chief engineer of WCAU, Philadelphia, Brown
measured elevation patterns of the WCAU antenna, which was also a Blaw-Knox
diamond tower. The measurements verified the results of Brown's model
measurements.

The results of Brown's research caused the FCC to require all further tower
installations as radiators in AM Broadcast operations to be of uniform cross
section, which in turn caused the demise of the diamond shaped radiator.

Another of Brown's many antenna research projects resulted in the present
ground radial system for AM BC antenna systems that became required in early
1940's, displacing the less than optimum counterpoise. His ground radial
research is well known as the Brown, Lewis and Epstein report, published in
the Proceedings of the IRE, June 1937. Althought many AM BC stations use 120
radials, the FCC requires only 90. The Brown research used 113 radials,
which has caused many to question the reason for 113. The reason is that
Lewis and Epstein were plowing in the radials for the experiment, and when
they had plowed in 100 radials there was some wire left over. They asked
Brown what they should do with the excess wire and he replied, "Plow it in."
The remaining wire produced 13 additional radials.

How do I know this version is true? I had the privilege of working with
Brown and Epstein while employed with them at the Antenna Laboratory of the
RCA Laboratories, AKA, The David Sarnoff Research Center. Story told to me
by the participants--no second-hand story here.

Concerning historical information on the early days of radio development
there are two limited volumes written by Gleason L. Archer, published in
1938 and 1939 by the American Historical Society, Inc., and printed by
American Book-Stratford Press, New York. The titles of the two books are
"History of Radio to 1926," and Big Business and Radio." Hopefully these
volumes will be available in some libraries. The details presented in these
books are phenomenal, with many first-hand quotes from the participants.

Walt Maxwell,W2DU