Di-Rectional.....

[Dan.Strassberg]

The first DA in the US went on the air in the early 1930s--sometime
between 1931 and 1934, I think, at WFLA/WSUN 620 in Tampa/St
Petersburg FL. The history of this early system is pretty well
documented on the Web. I can't list URLs, but a Google search for
WFLA/WSUN directional antenna should yield info on the original system
(probably mixed with info on later systems at these and other
stations--both call signs are still in use in the Tampa Bay
area--although for sure, WFLA is on a different station and so, I
believe, is WSUN). My understanding is that there were medium-wave DAs
in Europe before the WFLA/WSUN system--but not MUCH before. The
WFLA/WSUN system was followed in pretty short order, also in Tampa
Bay, at WDAE, which was probably on 1210 or 1220 at the time.

WFLA/WSUN shared time on 620. Probably because of the long salt-water
path to the north, nighttime-skywave interference to co-channel WTMJ
Milwaukee prompted the FCC to warn the Florida stations that, unless
they could eliminate the interference, their licenses would be
restricted to daytime-only operation. The original WFLA/WSUN phasing
network consisted of a length of coaxial transmission line, which had
to be tediously shortened to tune the array. The WDAE system was the
first to use discrete passive components for this purpose--a much more
practical approach.

Medium-wave DAs as we know them depend on the elements being vertical
radiators, which were just coming into use in the US at about the same
time as DAs. At that time, many stations used horizontal-wire
antennas; the (grounded) towers were merely for support. The
horizontal wire or wires that joined the tops of the towers were the
antenna. The vertical wires suspended from the middle of the
horizontal wire were feed wires and were not radiating elements.
Eventually, a few of these horizontal long-wire systems were converted
to DAs by shunt-feeding appropriately phased signals to the supporting
towers, converting the feed wires to a radiating element, and
insulating the horizontal wire or wires from the towers and what had
been the feed wires, thus converting the horizontal wires to a
(capacitive) top load. In the US, horizontal-wire antennas gradually
disappared over the next decades, although at least one remains in use
at KYPA Los Angeles.

The technology behind AM DAs has not fundamentally changed in the more
than seven decdes of their use but the mathematical tools for
synthesizing arrays has improved enormously. The method of moments, a
technique originally developed in conjunction with the H-bomb program,
is now embedded within array-synthesis software. One array designer I
know uses a supercomputer comprising 32 Pentium-class PCs to perform
the calculations. All of the computing power reduces to hours
calculations that not many years ago required weeks.

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

----- Original Message ----- 
From: "Don A" <donald_astelle@yahoo.com>
To: "Dan.Strassberg" <dan.strassberg@att.net>; "BRI"
<boston-radio-interest@rolinin.bostonradio.org>
Sent: Saturday, September 01, 2007 11:52 AM
Subject: Di-Rectional.....


> Maybe Dan or some other technical mind can answer this.
>
> I know the first (licensed) stations on the air around 1921-ish....
>
> When did the engineers discover directional antenna patterns?
>
> What year did the first directional array go into effect?
>
> The technology (if you can call it that) has been around for a long
> time....but seems rather "hi-tech" for the 20's and 30's.....
>
>
>