Vertical medium-wave transmitting antennas--WAS Re: WBZ/Westinghouse/Springfield, MA

[Dan.Strassberg]

Even though vertical radiators, whether base insulated and series fed
or grounded base and either skirt- or shunt fed, are virtually the
only types of medium-wave transmission antennas now used by US
broadcasters, such antennas had not yet been invented when (AM)
broadcasting started in the US around 1920. I'm not sure when the
first vertical antenna went into service in the US, who invented it,
or which station was the first in the US to use a vertical antenna. (I
may have read somewhere that it was in St Augustine Fla, but I am
hardly sure of that.) The first vertical transmitting antenna just
about had to date back to the late '20s. The first directional AM
antenna in the US went on the air at WFLA/WSUN Tampa/St Petersburg in
1931. Since DAs just about demand vertical radiators (and the
WFLA/WSUN antenna used a pair of them), the vertical radiator had to
have been invented by 1931. AFAIK, when the US's first boom in station
construction took place in 1922, NO station used a vertical antenna.
You will note that the antenna shown in the FCC logo is a horizontal
"long wire." I think the FCC had been the FRC (Federal Radio
Commission) until 1934. I don't know for sure that the new agency (the
FCC) had a new logo designed to go with its new name (could simply
have continued using the old FRC logo--if the FRC had a logo--and I
don't know whether it did or didn't, although I have never seen an FRC
logo). Anyhow, the logo suggests that long-wire antennas were still
quite common in the mid 1930s.

Mexico, Europe, and other parts of the world use types of AM
transmitting antennas that the FCC does not allow. Some of these are
really whacko ideas whose inventors claim remarkable properties for
them that pretty much defy the laws of physics and electromagnetic
theory. Others are valid and were used in the US in small numbers
before the FCC outlawed them. One is the two-element DA that uses only
one tower. Versions with more than two elements are possible--at least
in theory. Although this particular unconventional antenna in-fact
uses vertical radiators, only one radiator in the multi-element
antenna is a tower; the other (or others) are vertical-wire elements
suspended from the guy wires that support the single tower.

Two relatively recent unconventional antennas that look a lot
different from standard vertical radiators are really variations on
the vertical-radiator theme. These are the Valcom fiberglass whip, a
relatively short, self-supporting, fiberglass pole that requires no
guys and contains a helically wound radiating element with lumped
center- and top loads that increase its electrical length way beyond
its physical length, and the Kintronics KinStar, which uses a very
short vertical element and a massive capacitive top-load supported by
(in effect) telephone poles. The real magic of the KinStar is the
matching network, developed by Ron Rackley of duTreil, Lunden, and
Rackley, which allows existing AM transmitters to drive what would
otherwise be an impractically low base impedance.

Smaller capacitive top loads are common enhancements to conventional
vertical antennas. I think the idea of the top load is very old and
probably dates back to early efforts to convert horizontal long wires
into vertical antennas. The conversion was accomplished by turning the
vertical feed wire that drove the horizontal antenna into the
radiating element, whereas the former horizontal radiating element
became a capacitance to ground that altered the current ditribution in
the vertical element so that the current vs distance above ground very
closely resembled the current vs distance in the lower portion of a
much taller vertical antenna with no top load.

Any corrections or contributions of historical notes would be most
welcome!

-----
Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367

----- Original Message ----- 
From: "Doug Drown" <revdoug1@verizon.net>
To: "Roger Kirk" <rogerkirk@ttlc.net>; "Scott Fybush"
<scott@fybush.com>
Cc: "Boston Radio Interest" <boston-radio-interest@bostonradio.org>
Sent: Friday, March 28, 2008 3:33 PM
Subject: Re: WBZ/Westinghouse/Springfield, MA

>>
>> Scott Fybush wrote:
>>> The two towers, which are still standing, supported a wire
>>> antenna, no longer present, that was strung between them. The
>>> antenna was made up of a vertical feed that ran to a horizontal
>>> wire dipole...hence, a "T."
>>>
>>> The towers themselves were just support structures for the antenna
>>> itself.