On Sun, 23 Jul 2006 06:24:02 +0100, "Reg Edwards"
wrote:


"Walter Maxwell" wrote
The graphs reporting BLE's measurements are pretty conclusive. In
addition, the
BLE paper is the basis on which the FCC set the requirements for
the
ground
systems on all AM BC stations since 1939

==========================================
My point is that when there is a sufficient number of radials of
sufficient
length to approach a nearly-perfect ground, the ground
characteristics beneath
the radials are irrelevant within the area they cover in determining
the
terminal impedance and efficiency of the radiator. Therefore, the
different gr
ound characteristics that prevail as the frequency increases above
3.5 MHz are
also irrelevant.
Walt, W2DU
============================================

Dear Walt,

At risk of upsetting a great number of patriotic USA citizens, all BLE
hero-worshippers, I admit to having speed-read BLE's lengthy paper
some years back. Their conclusion, that with a sufficiant number and
length of radials the ground characteristics are irrelevant, is so
glaringly apparent they could have stayed in their offices and saved a
great deal of expense and copper wire. I am reminded of John Cleese's
remark "They must have had first-class honors degrees in stating the
bleeding obvious".

Because BL&E omitted to measure ground conductivity and permittivity
on the site their conclusion amounted to making a virtue out of a vice
and Marzipan the Magician's magic number of 120 came into existence.
Their sponsors should have made them go back to finish the job.

In the absence of any other information at the time, the fact of
irrelevance was of interest to LF and MF broadcasters with money to
burn, but it was, and still is, of no use to radio amateurs, confined
to the HF bands with limited purses, small back yards and XYL's to
keep happy.

My small program Radial_3 has been singled out and I have been accused
of disagreeing in a disruptive, almost criminal manner with BL&E's
conclusions. This is patently untrue! The program has nothing to do
with BL&E except that it deals with a similar subject in terms
appropriate to amateurs and draws its own independent conclusions.

Your absence caused a little worry. Glad to hear you were only
working.
----
Reg.

Reg, I appreciate your worry about my absence.

However, concerning the 'obviousness' of the conditions when there are enough
radials to simulate perfect ground, you must remember that it was not 'obvious'
in 1937. Prior to that time most BC 'aerials' were in the form of a 'T', a
horizontal wire (top-hat loading) supported by two towers, dangling a vertical
wire (the radiator) from the center, down to the antenna tuner. The 'ground'
system was a wire counterpoise, because very little was known about any other
type of 'ground' to work the vertical against.

Brown originated the concept of radials to improve the conductivity (meaning
reducing the resistance) of the ground, simply to avoid the construction of a
messy arrangement of wires to get tangled up in. But before presenting the
suggestion of radials to the world he proved it would work by performing the BLE
experiment.

Brown also is responsible for the tower antennas being of uniform shape over its
entire length, where before it was customary to use the diamond shape. With the
diamond shape the field strength measurements didn't follow the theory. Using
models for measurements he determined that the current on the diamond shape does
not flow uniformly, which resulted in undesirable radiation patterns. He then
demonstated that when the tower construction was of uniform cross section the
current became uniform and the radiation patterns became uniform and more
predictable and useful.

After proving the concept with models, he worked with John Leitch, chief
engineer of WCAU Philadelphia, in proving that it worked with full-size towers.
The WCAU tower was diamond shaped. The experiments with WCAU, and subsequently
with a tower of uniform cross section, proved the concept to be correct.

The result of Brown's experiment with the shape of the tower is that as of 1940,
the FCC mandated use of towers with uniform cross section for all new
installations. In addtion, no changes of any kind in the transmitting system
were permitted in stations that didn't already have a tower with uniform cross
section until the present antenna system was changed to one having uniform cross
section. Brown's influence on BC antenna systems is legendary. He also patented
the concept of using loading coils to shorten the physical length of towers.
Some towers that followed his lead have insulators between sections and an
inductance connecting them.

Brown's article, "Directional Antennas," appearing in a 1937 issue of the IRE,
formed the theoretical basis for all directional BC antennas

Brown also invented and patented the ground plane antenna for VHF and UHF. All
of his antenna experimentation was as an engineer with RCA. It was a great
experience for me to have worked in Brown's antenna lab along with guys like
Jess Epstein, O.M. Woodward, and Donald Peterson.

Walt,W2DU