How do broadcast towers work?

What if you need a directional array to operate ?

 

Do you see a problem? Will not Maxwell's equations for EM energy still apply, as would the rules for superposition, constructive and destructive 'wave' interference?

Plus, Kintronic endorses the concept:

Multiple Kinstar antennas can be arrayed for directional applications.​

From: https://topbandhams.com/Tech/Testing.pdf

 

http://www.snulbug.mtview.ca.us/books/RadioAntennaEngineering/
Radio Antenna Engineering was published in 1952, and presents an excellent overview of the state of commercial antenna system engineering as practiced in the first half of the 20th century.
You may enjoy reading this book, which is available as a free download.

 

I visited KUDI's antenna/transmitter site near Great Falls, MT in the early 70's ( Malmstrom AFB). In the doghouse there were traps for nearby AM transmitters to minimize IMD products. Is this still the case for modern AM BC sites? Now I wish I could remember the call of the ham who invited me to the site

 

Absolutely. Having two transmitters on different frequencies feeding the same tower(s) is another reason for bandpass/bandstop filtering.

It’s also common to see detuning skirts (wires) added to towers near directional AM facilities to reduce the effect on the nulls which typically protect other stations from interference. This would apply to any metal structure within a certain distance of a DA including communications and even water towers.

 

Good question re: IMD. The Harris line has used the technique described in this e-mail for awhile now in their "DX" series transmitters (like DX10, DX50 etc), this technique may result in a little less IMD being generated:

http://lists.contesting.com/_amps/2016-12/msg00419.html

Maybe I should look at the Harris DX line datasheet next.

 

At my last job in commercial broadcasting, We diplexed a 1620 expanded-band station onto the center tower of a three tower directional array on 1290. The same group had a station on 1180. It was a DA-2 meaning that it was directional with two different patterns day and night. IIRC, it was a 3-tower array nights and a 5-tower array days, plus different patterns during "Critical Hours" when gray-line propagation would happen. two phasors and 10 monitor points...WHEW! I am so glad that my current fifty KW blow-torch is non directional and daytime only!

 

WB5WPA - Wow. Thanks for sharing. So only 26’ high and 207’ diameter if centered on 1.9 MHz. Do you think it would hurt the performance if I grow hops from it? There’s no HOA here, just the XYL-OA. She would certainly approve it as a hops support structure. I can hear myself already, “Gee Honey, maybe I can use this as an antenna since the deer are eating all the hops anyway.” The hard part will be finding a flat spot that’s a couple hundred feet wide.

 

Shouldn't make a bit of difference RF-wise and you'd have the extra benefit of being able to say that your antenna was totally homebrewed.

 

Ok everyone, I did not intend to kick off a 7 page discussion on giant antennas, but I am not upset about it! This has been a fun thread to follow and I have learned much more than I expected, so thanks for that. Keep it going if there is more to say, I'll be lurking around trying to soak up as much info as possible