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Early AM Transmitting Antennas

T

trusty

After noticing that early AM transmitting antennas were basically wires strung between two towers, I tried to find a website that told me about when the change to vertical antennas took place - and if ground conductivity was the reason for the change. So far, I've had no luck, so maybe you can help satisfy my curiousity, or show me where I can find the answer.

Thanx in advance..
 
The efficiency of the verticals is better. In the early days, many AMs had a "T" arrangement where the vertical did the radiation, and the horizontal part was mostly a "capacity hat" to increase current in the vertical section.
Such low mounted antennas were often easy and cheap to build.
As many stations were in city centers, the absorbtion losses into water pipes, steetcar tracks, and building framework steel was considerable. Electrical noises (like streetcars) within the near area got into the audio.
Without the ground radial systems used with verticals, much of the power disappated in local ground losses could not be collected and
returned to the RF common point to increase the efficiency.
As the industry learned these facts, the move away from horizontal antennas for AMs began.
Late 1920s and into the 1930's most stations switched if they could.
At some point the FCC required minimum radiation efficiency which such horizontal antennas did not meet.
They ARE permitted for emergency use, as when a tower collapses.
 
...the vertical did the radiation, and the horizontal part was mostly a "capacity hat" to increase current in the vertical section.
Click to expand...

Cool. Just one more question (I think.). Was the length of the the horizontal part cut to the wavelength (or half or quarter wave) and serve the same purpose as the height in today's AM antennas? (It looked like the vertical line was just a "lead" to the horizontal top of the "T".)

Tnx.


;)(I know just enough to get into trouble, but not enough to get out.)
 
That's what I thought too about the horizontal parts, but as I have come to understand later, the vertical part did the work, and part of the inefficiency was the less-than ideal length of what most station put up as the vertical.
 
That's what everyone thought back then. It's only in recent years, with the advent of computer modeling, that the understanding has developed that those "horizontal" antennas generally behaved as very short verticals with lots of top-loading.

I've been doing some research (with considerable help from Ben Dawson of Hatfield & Dawson) into the earliest vertical towers, and the general consensus we've come to is that the very first vertical towers went up in 1931 at New York's WABC (now WCBS; the 1931 site was at Wayne, NJ) and at WAAB/WNAC in Boston. Both of those towers were the Blaw-Knox "diamond" towers, as were the next ones that went up in 1932 at WSM and WLW. WSM and WLW are the oldest verticals still standing.
 
I read something about "...NBC engineers working to improve WGY's signal with a vertical antenna..." (or something like that) Do you know when WGY's vertical tower first went up?
 
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